Assisted Pedal Cycles. Converting an existing bike using the
Bafang BBS01 Mid-Drive kit
Installation, gear-ratio optimisation, and review.
by David Knight
Click image to view enlarged in a new window.
The terms "Electrically Assisted Pedal Cycle (EAPC)", "Pedelec" and
"e-bike", can have various meanings; but the most common, and indeed
the most useful, definition is: 'A bike that provides the
with a degree of electrical assistance, but is regarded in law as a
pedal cycle.' This means that the e-bike of common usage can
ridden without registration plates, road tax, roadworthiness
certificate (MOT) and
insurance (at time of writing),
and the rider does not need a driving license or a type-approved
helmet. In the UK (excluding Northern Ireland), the basic
requirements for such an exemption are that it must be possible to
propel the vehicle using pedals, the electrical assistance must stop
when the speed reaches 15.6 mph (25 km/h), and the motor power must not
exceed 250 Watts. In the UK also, there is a minimum age
of 14 years.
People from all walks of life seem to
like the idea
of owning an e-bike; but there is a particular attraction for those who
would like to do a lot more cycling but must realistically admit that
never going to achieve the necessary level of fitness. Such is the case
the author, who underwent an operation for a replacement aortic valve
2012, has some permanent heart muscle damage as a consequence of the
valve failure, and is separated from his local town (Ottery St Mary) by
mile (1.9 km) long
stretch with a height difference of about 90 m. Thus the road
most need to use has an
average gradient of around 1/20 (i.e., 5%). Going down to
therefore no problem, but coming back again without stopping to rest
potentially life-threatening experience. I notice also, that
perfectly able-bodied neighbours don't like cycling up the hill either,
and show a general preference for 4×4s.
There are two routes to owning an
e-bike. Such a vehicle can be bought outright for the price
of a fairly good second-hand car; or for those who might question the
sense of paying thousands of UK£ for a push-bike with a
battery and a 1/3 horsepower electric motor, it is
possible to convert
existing bike. In the matter of conversions also, there are
two principal choices; that of fitting a motorised wheel, or that of
motorising the pedal-drive system; the latter being known as a
Mid-Drive or M-Drive conversion. The motorised wheel option
seems to have little to recommend it for people who live in hilly
terrain, because it lacks any method for
changing the gearing ratio. The most straightforward approach
also involves the
front wheel, and so will make the steering heavy. So it
for the fiscally prudent hill dweller not afraid of bike maintenance, the
M-Drive is the obvious solution.
The huge advantage of an M-Drive system
is that it provides electrical assistance directly to the pedals.
This means that it operates through the existing rear gear-changing
and so, in principle, can provide high torque when
configured with front and rear sprockets having suitable numbers of
Thus diverse mobility requirements can be
accommodated, but that does not necessarily mean that you will be
supplied with the right ratios at the outset. It
is also the case that an M-drive kit will require removal of the front
dérailleur, if provided, generally eliminating the small
At this point, assuming that you decide
to break the
law (advisable, see legal info
a good choice of M-Drive system is the well-designed and reliable
Bafang 8Fun BBS01 (or one of the various re-branded
versions of it). At the time when this project started, the BBS01 was
practically the only road-legal choice; but there are now other options
who care to look into the matter.
Some initial thoughts on
gearing and choice of bike
A straightforward approach to carrying out an e-bike conversion is to
start with a modern mid-priced bike that uses a cassette-type
rear dérailleur system; a cassette being a set of sprockets
designed to fit onto a splined freewheel hub. This allows cogs to be
changed easily and inexpensively during maintenance and to optimise
gear ratios. Another possibility would be to put together an e-bike
that uses rear-wheel hub gears, but obtaining a wide range of ratios is
then going to be expensive. Adding a motor unit and battery will add
about 8 kg to the overall weight, so the chosen bike should be a tough
workhorse not a lightweight thoroughbred.
I own a Saracen
Tufftrax Comp Disc 29
mountain bike, which, as the name
implies, has 29" wheels This came with an
tooth Shimano 9-speed rear dérailleur cassette, and a
chainwheel with a choice of 44, 32 or 22 teeth (i.e., a 3×9
chainwheel is for going fast on good roads, and has proved to be of
little use in
the cramped streets of Ottery and the pot-holed single-track lanes
through which my house communicates. Also, it has to be said
that, since heart surgery, I don't have the stamina needed to make
the bike go fast in top gear; and the fitting of a mechanical aortic
valve requires that I take Warfarin to keep my blood-clotting time
between 2 and 3 times that of a normal person. I therefore
cycle defensively, and usually pull to the side and stop
when I meet other vehicles in the lanes. Given the dire consequences of
falling off, I also don't go particularly fast downhill; and it
that I would barely notice if I didn't have the 44T chainwheel. This
was of concern because the fitting of a Bafang BBS01 drive involves
discarding the front dérailleur and
fitting a single front
chainwheel, with options of either 44, 46 or 48 teeth using
Bafang-supplied parts. That would put the
bike permanently into my top front gear or even higher; and I find it
hard to get going from standstill in 44/32 (1.375:1).
Changing to a 12-36T mountain bike (MtB) cassette
with the smallest Bafang chainwheel, which is somewhat better, and of
course, the whole point is that the motor supplements the rider's
strength; but the bike essentially becomes unusable
once the power is off.
As an alternative to fitting the
front chainwheel, people also manufacture adapters (known as 'spiders') that can be used to
mount non-Bafang chainwheels. These are available for bolt
diameters (BCDs) of 104, 110 and 130 mm. The problem here
is that the standard Bafang chainwheel is dished to bring the chainline
towards the body of the motor. The use of a smaller
therefore does not allow such a good chainline; introducing the
possibility of dérailleur adjustment issues and
increased wear. On the other hand, a 104 mm BCD spider allows
use of a 32T chainwheel, and 32/36 gives a very acceptable bottom
ratio of 0.89:1.
A further set of alternatives is
provided by various 3rd
party manufacturers who make Bafang compatible chainwheels. Some of
these sprockets are flat, and some are dished to improve the chainline.
Exact details of the design can however be hard to
obtain from the online information.
The difficulty, for me, at this point
accumulation of unanswerable questions. This eventually led me to the
decision that I
would not start by experimenting on my perfectly serviceable Saracen
I would instead get
hold of another bike to use as a test-rig. A straightforward and
modification for the Saracen however, was to fit a 12-36T rear cassette
and get a bit more mileage out of the 44T front chainwheel. This also
gave a somewhat balance-challenging bottom ratio of 22/36 = 0.61:1,
which was not particularly practical for ordinary roads, but was good
for cycling on the steep tracks found in this part of the
world. Note that when fitting a casette with larger sprockets, it will
be necessary to purchase a longer chain.
Once I had built my first e-bike, I soon got 'round to converting the Saracen to make a second one.
That was done
because the first conversion was very successful, and it turns out that
able bodied (but not particularly athletic) cyclists on ordinary bikes
can't easily keep up on hilly terrain with a heart patient on a
well-fettled electric bike. I therefore built the second bike
so that others could come cycling with me.
Apart from gearing considerations;
while changing the rear cassette on the
and thinking about the possibility of carrying-out an e-bike
conversion, I become aware of an annoying issue that might be worth
considering when selecting a bike. The Saracen has bare
in its gear shifter cables. For both shifters, a short length
Bowden-cable outer is used to get from the handlebars to a lug on the
of the top frame-tube. A bare steel cable then goes from this
point to a lug just in front of the saddle-post. Then, for
front dérailleur, a length of cable-outer is used to get
around the corner
to a lug on the down-tube to the bottom bracket. For the rear
dérailleur, a length of outer goes to another lug on the
fork, and a bare cable goes to the botton of the fork and back into an
outer for attachment to the shift mechanism.
I had been aware of the practical
arrangement for some time: it precludes attaching anything to the top
tube, it prevents the bike from being clamped securely onto a bike
adjustment, and it prevents the fitting of a universal luggage
rack. I had however previously not bothered to do anything
about it. Apparently it
reduces weight, but the net advantage of losing a few short lengths
of cable-outer and then having to weld a bunch of lugs onto the frame
seems marginal. It has also been said that it might reduce
friction; but while having to cycle through puddles is practically
unheard of in sunny England, there will eventually come a point when
the ingress of muddy water will make itself apparent.
For an e-bike conversion, any bare
sections are best eliminated. The front down tube is needed for
the battery pack, electrical cables run along the top tube, and
existing attachment points are used up and you'll want to create new
ones. Mercifully, the front dérailleur is removed
and that solves half the problem. For the rear dérailleur
however, you'll need to run a single-piece Bowden-cable from the rear
mechanism to the handlebars with
low curvature. You'll also need the tools and parts for making-up
Bowden cables, and the dérailleur will need to be readjusted
afterwards. None of this is difficult, but a layer of messing around
might be avoided if you're planning on buying a new bike.
A bike for all seasons
29ers are for tall people. I
am 1.80 m tall and my son Steve is 1.98 m. Both of us can use
the Saracen in comfort, but it does not suit other members
of our family or anyone else under
about 1.75 m. One consideration when carrying out an electric
is that others will want to have a go on it; and if adopters
of the technology can allow that, it promises to change attitudes
towards cycling (and
make the roads safer to boot). I
keep reading articles saying that e-bikes are a form of cheating; as if
cycling only attains validity by being
exhausting and causing the practitioner to need a shower and a change
of clothes. The truth of the matter is that cycling isn't
practical for the majority of people, because you don't arrive fit to
work unless it was walking distance anyway; so cycle rides tend to be
rare, and tend to be arranged so that they end at home. Thus
most people never attain the stamina and skill required to
cycling enjoyable; and a huge barrier to uptake exists.
With the ideas outlined above beginning
to form, but not yet fully realised, my son Steve and I went to the
cycle shop from which we had bought our existing mountain
a few years earlier. I must admit, I had been thinking of getting
another 29er; but Steve made the point that none of our other family
members would want to ride it, and it occurred to me that having
smaller wheels results in greater mechanical advantage
drive-train. So, after much discussion, I bought a Forme
1.0 mountain bike with 27.5" wheels; which also conforms to what I
be a basic requirement, which is that of having adjustable front
suspension and hydraulic
disk brakes. The bike had a 9-speed 11-32T Shimano Hyperglide
fitted originally; but this was swapped for a
12-36T, and the slim saddle was replaced with a
more testicle-friendly gel model for a modest extra cost. I
was also given a
couple of secondhand Shimano 32T 104 BCD steel middle chainwheels for
low-ratio experiments (see below
The Sterndale came with a triple front
chainwheel and dérailleur, which
obviously had to be removed for the electric conversion, and it is
worth noting that the middle cog from such redundant assemblies is
another possible source of 104 BCD sprockets.
A ride on the Sterndale before starting
to work on
it confirmed that the extra mechanical advantage (18.6%) given by the
cassette and the 27.5" wheels was very noticeable in comparison to the
Saracen's original 11-32T and 29" setup.
Twist & Go
The Bafang motor has an internal freewheel ratchet mechanism in
to the freewheel hub at the rear wheel. This means that the motor can
bike while the pedals stay still, and the facility to connect a
throttle control (accelerator) is provided accordingly.
Having a hand throttle or 'Twist
& Go' facility
on an e-bike is both convenient and a considerable safety advantage. It
permits the bike to pull-away
without wobbling at busy road junctions, in crowded traffic situations,
and when there are pedestrians around. It is also
particularly useful in getting going again when you have been forced to
stop suddenly without time to change down. There is however,
a legal peculiarity in relation to this matter: which is that newly
manufactured e-bikes require Government Type Approval if they are to
have a Twist
& Go control. Conversions carried out on bikes that
have previously been used on the public roads are however exempt from
that requirement (see legal info
The upshot is that, if you intend to
fit a throttle, you must convert a bike that has been used previously.
If you were to buy a frame and build an e-bike from scratch,
thereby sidestepping the expense of discarding a perfectly good
crank-set and front dérailleur, that action would
would result in a machine that requires Type Approval. The
might seem unprovable of course, but there is always an audit trail if
someone wants to cause you legal difficulties.
Installing a Bafang
M-Drive on an existing bike
Presuming that you have a bike that you want to convert, and that you
have a Mid-Drive kit waiting to be installed; the first job is
to remove the front dérailleur (if present).
This is the point at which most online
commentators assume that what they needed to do is universal, and some
actually recommend that you destroy parts of
mechanism with wire cutters in order to get the chain off.
You don't need to destroy anything, but you do need to own
chain-splitting tools and Quick-Links, even if you don't require them
In some cases there will be a screw on
the chain shifter that
be taken out, enabling the mechanism to be opened-up and removed
splitting the chain. On the recently manufactured Shimano shifter on my
Sterndale however, there was a place for the screw in the pressing, but
the two parts had simply been welded together. Thus I needed
remove the chain, but I found that it had been supplied with a Quick
Link already fitted. If you read about Quick Links online,
say that they are unreliable. I asked about this at the cycle
shop, and was told that such links are perfectly reliable; and
practice of pushing chain pins back in with a chain splitter is the
greater source of breakages. To
Quick Link requires a set of special pliers. Some Quick Link
pliers can also close the link (i.e., force the rollers apart), but
this operation is also fairly easy to accomplish by assembling the link
and tugging the chain. If you part the chain using a link
extractor and then fit a Quick Link, note that the links come in
different widths (8, 9, 10 or 11 speed) depending on the number of
sprockets on the rear cassette, and there are both single-use and reusable types.
The next operation is to remove the
It's best to do this while the cranks are still on the
bike, otherwise you will need to hold each crank in a vice and risk
A 15 mm open-ended spanner is usually required. The
side of the bike (the side opposite the chain side) has a left-hand
Removal of the cranks from low-end and
mid-price bikes requires a
special tool known as a 'crank puller'. Before buying a crank
puller, you need to take out a retaining bolt on the crank-set you
intend to detach and have a look at it. The Bafang 8Fun uses
a 'standard' old-fashioned square-taper fitting, but more modern bikes
will often have a splined crank. Shimano Octalink®
cranks (as the name implies) have an 8-lobed spline, and Isis®
have 10 lobes (and there may be others). The splined
cranks can only be removed with a standard crank puller if there is an
additional anvil piece to fit into the end of the crankshaft. I got
caught-out by this, but I have a lathe, so I was able to make an
adapter out of a piece of mild-steel bar in about 10 minutes.
The item I made is functionally identical to the Shimano
TL-FC15 (see list of tools
the end of the article).
Octalink sealed crankshaft unit with crank puller and adapter.
The top-hat shaped piece fits into the end of the crankshaft,
allowing the bolt in the crank puller to push against it.
Once the cranks have been removed, it's
time to remove the bottom bracket. This requires a special
tool with a 20-lobed spline that fits into the retaining nuts on either
side. This is the point at which you have an opportunity to
ruin the nuts, destroy the tool, skin your knuckles, and write a
venomous feedback article casting doubt on the tool-seller's parentage.
Alternatively, you might try using the thing properly.
You will notice that the tool has a
it to be turned using a wrench or spanner, as well as a socket for
a ½" ratchet wrench. There is a very good reason
has both. It is usual to see explanations of how to remove a
bottom bracket in which the commentator snaps the tool onto a ratchet
drive and (supposedly) turns the nut. That might work, or it
might not; but the second possibility is extremely likely. If the nut
has been in place for any length of time, it
will probably have encountered its fair share of rain and mud.
Assuming that you do not own a
pneumatic impact wrench, a reasonably stress-free way of
loosening the nut
is to hold the tool in place using a G-clamp, with a block of wood on
the opposite side to protect the paint or the protruding crankshaft
(see illustration below).
An open-ended spanner or wrench can then be placed on the
hexagonal part; and a sharp, but not particularly hard, tap on the
spanner with a soft mallet should free the nut. What happens
here is that the shock of tapping the wrench shatters the crystalline
structure of any rust, dirt or adhesive in the thread.
The G-clamp can then be removed, and the nut can be unscrewed
using a ratchet drive.
If using an open-ended spanner doesn't
work; it is
possible to insert a 2 ft breaker bar into the tool and hold it into
the bottom bracket with a G-clamp as before, but with a second block of
wood to protect the breaker. It takes two people to hold this
arrangement together while doing-up the clamp, but it does loosen the
most belligerent of nuts.
Holding the bottom bracket tool in place with a G-clamp
while persuading the nut to turn. The sprocket-side nut has a
left-hand thread. If the nut is very stiff, use a proper
open-ended spanner (24 mm or 15/16"), not an adjustable.
Another reason why people destroy the
bottom bracket tool is that the nut on the sprocket side has a left-hand thread
needs to be turned clockwise to undo it.
Note incidentally that, for the Shimano
Octalink and other sealed crankshaft units, it is convenient to remove
nut first. That withdraws the complete shaft and bearing
assembly. The nut on the other side is merely a sleeve to
the shaft straight in the bottom bracket.
Once you have removed the crankshaft
the bottom bracket without wrecking anything or injuring yourself, you
are free to install the Mid-Drive motor unit. Furthermore, if the
author's experience is anything to go by, the procedure is then quite
closely related to the information given in the various versions of the
That all depends however on the bottom bracket being
"standard", which means that it must measure between 68 and 73 mm from
one side to the other. You can estimate this approximately by waving a
ruler in its general
before the crankshaft and pedals have been removed.
The thread around the crankshaft on the
Bafang motor unit is M33×1.5. The motor is held
bottom bracket by a hard steel M33 castellated round-nut, which is then
covered over by a splined aluminium-alloy locknut. The outer
hide the castellations of the inner one. It can be difficult
get the steel nut as tight as it needs to be to stay done up for a long
time, and a good quality C-spanner (hook wrench) is needed. Also, the
locknut has to be unscrewed if you want to check the tightness, and
this requires removal of the pedal.
Early versions of the 8Fun just had two castellated nuts,
being a less attractive but more secure arrangement.
Hard steel castellated nuts can be ordered online (on ebay for
example - try "round castle locknut"). Note that stainless
is also hard and has the added benefit of corrosion resistance.
stainless steel castle nut with the Bafang supplied nut used as locknut.
I actually bought a BBS01 kit with a
chainwheel, but then bought a 44T chainwheel separately as an
afterthought. Both of these sprockets came with a plastic
chainguard, the 46T version having a larger diameter than the 44T
version. Both guards however have the same hole circle
for the fastening screws, so the large one can be used with the smaller
sprocket if so desired. I first commissioned the bike with a
fitted, but later left it off on the basis that flared trousers went
out of fashion over 40 years ago. It might conceivably
the chain from jumping off on the outside on rough terrain, but it also
prevents access to the five Allen screws that
hold the chainwheel to the motor shaft, making it difficult to check
tightness or swap chainwheels. Being plastic, the chainwheel
cover is of little use as a bashguard; and a sprocket guard is in any
case not sufficient to protect the BBS01 motor because there are three
electrical cables coming out of
the bottom of that. Riding without grounding the motor housing is
unless some kind of engine guard plate (motorschutzblech) is devised.
a guard is available for the BBSHD, but there are no obvious
attachment points on the BBS01/02, which means that it would have to
attach to the bike frame.
The Bafang motor unit has square tapers
on its crankshaft. The subject of fitting crank arms to such tapers has
generated considerable and sometimes heated discussion in the numerous
web fora; all of which can be summarised fairly succinctly by saying
that no one seems to know what to do. The problem is that; while the
process of doing up a bolt normally has an obvious end-point, this is
not the case with bolts that draw the two parts of a taper system
together. This issue is also particularly troublesome when one of the
parts (the crankshaft) is made of hard steel, while the other (the
pedal arm) is made of aluminium. An ordinary Allen key isn't long
enough to achiveve the required tightness (NEVER us a hammer); and
while a socket wrench with an Allen bit can do the job, it is
impossible to decide when to stop. If the bolts are too loose; the
pedal arms will creak and click, they will keep falling off, you might
lose bolts on the road, and the taper fittings can be permanently
damaged. If the bolts are too tight, the fittings can be permamenetly
damaged, and the arms will be very difficult to remove.
Under such circumstances, there really
is no alternative but to use a torque wrench. It does not however need
to be one of the expensive (and uninformative) click types; and in the
author's opionon, the low-cost beam-deflection indicator type is
perfect for this job. The type of Allen key that fits onto a
socket wrench is incidentally known in full as a "Hex Allen key bit
socket". The size required for pedal crank bolts is 8mm. A ratchet
'adaptor' between the the torque wrench and the Allen bit facilitates
the job considerably; but a good quality (>500 Nm rated) adapter
is likely to cost more than the wrench.
With a torque of around 40 Nm, the
crank will pull slowly onto the taper. Grease doesn't make much
difference. Keep going until the bolt slows down and stops. Tighten
both cranks, then go for a short ride to make sure that they don't
creak or click under load. If they do, tighten them a bit more. When
all is well, put an ordinary 8 mm Allen key into the road toolkit, just
in case, go for a longer ride, and check again. Check the tightness
Ratio tables for various
chainwheel sizes and some MtB cassettes.
given in the tables below are the number of
turns of the back wheel
per turn of the pedal crank. To get the distance travelled or 'metre de
développement' (measure of progress), multiply
the ratio by πD, where D is the effective diameter of the back
Distance / cycle = measure of progress = πD
= front sprocket teeth
= rear sprocket teeth
D = back wheel outer diameter
If you've just upgraded from a penny farthing and want this
"gear inches", leave out the π.
Gear inches = D × Tf
To convert from gear inches to progress per pedal rotation (in metres),
multiply by 0.0254π
The optimum penny farthing wheel
diameter for travelling on the flat was determined to be around 60", so
to upgrade to a bike with (say) 27.5" wheels, you need to gear-up by a
factor of 60 / 27.5 = 2.18. For 29" wheels, the gear-up factor is 60 /
29 = 2.07. This gear-up ratio of around 2 is useful
to remember when perusing ratio tables, because it is the figure
appropriate for shopping on the village high street (with a wicker
basket full of groceries on the front). Unless it can be comfortably
exceeded, the bike is going to be too low-geared for general-purpose
cycling on modern roads. Ideally, for 27.5" or 29"
wheels, the top ratio should be around 3.5 to 3.8 for faster roads.
chainwheel sizes listed below are
examples of what can be fitted on a BBS01/02 M-drive conversion, 44 and
46T sizes being made by
Bafang, a 38T being available as a
Hallomotor aftermarket product, 42T and 36T being made by PreciAlps
32T being made by mounting an
intermediate front sprocket on a 104 BCD spider
adapter. Other sizes can also
be made-up using aftermarket spiders; but the larger chainwheels can be
dished to give the best chainline, with 42T being the smallest size
that can be
dished in this way.
Shimano HG400 12-36T 9-speed cassette.
|Front chainwheel teeth
(smallest possible dished type is 42T)
There are also 48T
and 52T chainwheels made
by Bafang, but these are intended for small-wheeled bikes, and give too
top ratio for road use with bikes having a 12-36T cassette and 27.5" or
29" wheels (and have
far too many teeth for mountain biking). A recent trend however, has
been to increase the range of ratios available from the rear cassette
with a view to eliminating the front dérailleur altogether.
Since loss of the front changer is a matter of force majeure for e-bike
builders, and front sprockets having less than 42T are flat rather than
dished, these new systems are of considerable interest.
The table below is for the Shimano
Deore XT 11-46T cassette, which has a particular advantage over some of
exotic possibilities in that it can be retro-fitted to an existing
freewheel hub. Note how its use with the PreciAlps 42T
front chainwheel practically covers the entire ratio range of
the table above.
The change ftom 37T to 46T is large, but pedaling cadence is not
particularly important in a low gear primarily intended for off-road
Shimano Deore XT 11-46T 11-speed cassette.
|Front chainwheel teeth
Sunrace also make an 11-46T MtB cassette, model CSMX8
EAZ. This is Shimano compatible, but offers a more even ratio spacing,
the tooth numbers being: 46, 40, 36, 32, 28, 24, 21, 18, 15, 13, 11.
The Shimano and Sunrace 11-46T 11-speed offerings, combined
with the PreciAlps 42T front chainring, are reviewed
, and prove to be an excellent choice for those who wish
to combine road and off-road
capability in one drivetrain.
Another alternative for achieving a
wide range of
ratios is to build your own cassette out of individual sprockets.
Inexpensive cassettes are often supplied either as a pair of
sprocket stacks, or
as a single stack plus one or more separate cogs, the stacks being
held together by rivets. In some cases, the individual sprockets in a
stack have their own splines for engagement with the freewheel hub,
which means that the rivets can be removed. It is then possible to
achieve a wide
range by removing one of the smaller cogs in the series and adding a so
'expander' 'or 'extension' sprocket at the large end to give an extra
Extension sprockets can have as many as 50 teeth, but the clean pick-up
of a fully engineered cassette cannot necessarily be expected, which
means that very
large jumps are best avoided.
The ratio steps in the region of the
can be made more even by buying new sprockets, or by mixing sprockets
from several cassettes. Note however, that the smallest cog is often
serrated, to make it grip against the outer retaining collar; which
means that it must either be retained or replaced by another
similarly serrated cog. Special lockrings that allow the small sprocket
to be discarded are also available, but it is important to check
It is also possible to mix and match
cassettes with different numbers of speeds by using spacers. A 2 mm
spacer, for example, allegedly allows sprockets from 11-speed cassettes
used in 10-speed systems (I haven't tried it). 1 mm, 1.5 mm and 1.85 mm
spacers are also
available, some cassettes are built using spacers, and thin shims can
be made from sheet metal.
extension sprockets, and cassette modifications.
Singletrack World: Shinano Deore
XT 11-46T 11-speed casette
wide-ratio MtB cassettes
Aerozine expander sprockets
Black Extender Cog and 13T lockring
Hope 40T-REx expander sprocket
Toolth casette cogs
to adjust your dérailleur
Shimano HG50 cassette
Note that very large rear sprockets can require a longer than usual
dérailleur B (body) tension adjustment screw. This
adjustment sets the position of the jockey wheel (upper pulley)
relative to the
largest sprocket, the point being that the two should be
close without touching. This screw is just an
set screw (i.e., it is threaded all the way along its length). 'Extra
long' means 25 mm thread length or greater. A grub-screw, an
Allen-head, or a Phillips can be used. To avoid rusting, the
material should preferably be stainless steel A2 or A4.
An alternative to fitting a longer B
screw is fo fit a Wolf Tooth / Lindarets GoatLink
dérailleur hanger extension. The goat metaphor relates to
idea that the extension piece enhances mountain-climbing ability. The
to move the jockey wheel further around the cassette and position
it so that the extreme B adjustment is no longer needed. This
modification is said to improve shifting performance, and the
greater chain wrap will tend to reduce sprocket wear.
A commercial weakness of the Goat Link
while it might have taken a lot of R&D work to arrive at the
design, it is just a small metal component made using a CNC machine
tool. Consequently, while the genuine article can cost about
UK£28 (inc. shipping) at time of writing, there are
from China for around £2.
When a large range of ratios is
provided, it might be necessary to fit a long-cage
The cage length is the distance between the jockey wheel and the
In the lowest gear (largest cog), the tension pulley is
is at its furthest forward, and in the highest gear (smallest cog) it
is at its furthest back. A long cage permits a large range of movement.
Controls and wiring
Where the installation manual is justifiably vague is in the matter of
lay-out the connecting cables and fit the controls. Bikes
have a great deal of variability, and all that can be said with
certainty is that the job must be done in such a way that cables cannot
get accidentally crushed or snagged. There are
however a few specific issues worthy of comment.
I decided to fit a right-hand twist
throttle, the same configuration as is used on motorcycles. I
found a problem however, which is that the throttle was not compatible
with the control levers for my rear dérailleur. It was
not possible to get the shift control into a good ergonomic position
relative to the hand-grip with the throttle twist-grip in between.
So, it occurred to me that, since there was no-longer a front
dérailleur, I should move the shifter to the left-hand side.
My first thought on this matter was
that it might be possible to buy a left-hand 9-speed shifter, at which
point I made the mistake of looking for information online.
According to some of the web fora, this is a huge problem for
disabled people who lack the full use of the right hand. The
general view seemed to be that the issue is insoluble, although one
suggested 'solution' was to dismantle a 3-speed shifter and get a
machine shop to create a left-handed 9-speed ratchet
mechanism for it. I began to form the view that I should
discard the right-hand throttle and get a left-hand one; but then I had
a careful look at the bike and a strange heretical thought came into my
mind: 'Er. . . ., why can't I just take the shifter off the
right handlebar and put it onto the left one?' Five minutes
work with a couple of Allen keys and I had a left-hand rear shifter.
The numbers on the indicator were upside-down, and I had to
change down with my forefinger and up with my thumb; but so what?
Getting used to the arrangement while out riding took less than a second.
Incidentally, when I eventually
upgraded to a 1×11 drivetrain, the indicator on the Shimano
XT M8000 trigger shifter I fitted had no numbers on it, and it was then
not possible to determine that the control was on the 'wrong' side of
9-speed shifter on the left and twist throttle on the right. Notice
that the ratio indicator lies above the handlebar, rather than
sticking-out past it. If you want to fit a twist throttle, this is a
feature worth looking for when selecting a bike or a shifter, because
it gives more positioning options.
The Bafang kit is supplied with a pair
of brake levers that have motor cut-off switches on them. An
however, is that the included levers are only suitable for
brakes, they are of no use if you have hydraulic actuators, and they
also cannot be used if the bike has combined brake and
gear shifters. These limitations ensure that many people do
bother to install the switches (which are often said to be not strictly
I felt however that there might be an
retaining the kill-switch functionality, and so I ordered a
Bafang BBS magnetic brake-sensor switches. I presumed that these could
retro-fitted to a variety
brake actuators, a small magnet being attached to the lever arm using
an adhesive pad, and the switch body being attached to the fixed part.
This is a horribly crude arrangement, but I expected that it would at
least allow me to evaluate the effect . A problem I found when the new
switches arrived however, was that none
brake actuators were compatible with them; and while I could see
that I might be able to engineer some sort of secondary mechanism to
make them work, I certainly wasn't going to be able just to stick them
on. Riding without
kill switches was therefore the practical solution in the
Another serious downside of the crude magnetic
that the compass-safe distance is about 0.5 m, and there are two of
them. I like to have a small compass (Suunto Clipper
) mounted on the handlebars
because it provides
the simplest way of knowing where you are going when you're lost in the
woods. Having steel bike components in the vicinity introduces
small errors, but nearby magnetic switches render continuous compass
Subsequent riding experience suggested
that there would be a worthwhile ergonomic improvement in having kill
switches. This is because there can be a lag of several tenths of
a second between cessation of pedaling and the shutoff of power
assistance. It is perhaps not a major safety issue, because
the motor output is only 250 W and the bike brakes can absorb
the short burst of surplus energy; but any enhancement in braking efficiency is always welcome.
An issue that cannot be ignored
that when several people ride close together, there is a definite need
for brake lights. Also, most car drivers do not understand the
hand-signal for slowing-down, and keeping both hands on the handlebars
is anyway desirable in traffic. A brake light is therefore an obvious
inclusion when a
large battery is already available. Brake switches then become a
necessity; and they might as well also operate the motor-kill function
(e.g., by using a transistor as the kill switch).
The presence of the battery, and the
of high efficiency LED light sources, suggests that the e-bike should
take advantage of the safety improvements that can be gained
having the full set of motorcycle lighting equipment; i.e., a dual beam
headlight, indicators, a tail light and a brake light. In the days of
tungsten lamps, such additions would have reduced the range
significantly, but this is no longer the case. The provision of all of
this extra equipment however requires actual engineering work, rather
than the fitting of pre-manufactured parts, and it will therefore be discussed in a separate article: e-bike lighting and electrics
The setting-up procedure given in the manual is actually pretty
straightforward and does not take long. There are however two
peculiarities worthy of mention.
One necessary aspect of setting-up is
to input the bike's wheel size. It would be good if the wheel
diameter could be put in accurately, say to the nearest 0.1", but the
options are limited to standard sizes. In the case of a bike
with 27.5" wheels, it is necessary to put in "700c", but this is not
always an exact definition. It is good enough to avoid a
conviction, but a
little annoying if you are a lover of precision.
A wonderfully cryptic item in the
advanced setup menu is "Level amount setting". This sets the number of
increments that are available on the handlebar control when selecting
the pedal-assistance level. The choice is from 2 to 9, with a
factory default of 3. On one web forum, I saw a thread discussing the
discovery of 'secret extra power levels', and how the performance is
enhanced by going up from the default of 3 to the full 9. The
only trouble is that there are no extra power levels. It's
just a setting for the interval size. Three levels is a good choice,
and it certainly beats the tedium of having to press the (+) button
eight times to get to full power.
The e-bike battery
To power the bike, I bought a TLH 36V 15.6 Ah
Li-ion battery with charger. This came without
or instructions; but its operation seemed to be fairly
There is an LED status indicator that lights at the press of
button if the charger is plugged in and switched on, or if the battery
is switched on. A mounting plate and connector fits onto the
bike-frame down-tube, the
battery unit slides on to it and is locked into place using a
supplied key. An immediate issue I had with the Sterndale
frame however, is that there was only enough room for the battery on
the front down tube, and the battery-plate bolt holes were too high-up
to mate with the bottle holder attachment points. The work-around was
mount the battery upside-down. I also found that the heads of
M5 Allen screws that came with the bike were too proud to allow the
battery to slide onto the plate; and the solution was to
replace then with A4 stainless hex-head M5×12 screws
The mounting plate system allows the
battery to be
taken away for charging or
storage, but there is no obvious reason why it cannot also be charged
in situ. I feel however that, given the high energy-density involved,
charging should be done in an
outbuilding, or somewhere with a smoke alarm, and certainly not in a
building where people sleep. The battery charger gets quite warm
in use, so is best placed on a wire trivet, or a luggage
rack, or otherwise
suspended so that air can flow over it. Charging the battery
half to full takes about 3 hours; and the charger is small enough to
take with you if you are going somewhere with mains electricity.
Once charging is complete, the LED on the charger changes
red to green and the charger cools down (i.e., the charging current is
My battery installation, unfortunately,
developed a major problem after a few days riding. This was
to do with the
electrical connection between the battery housing and the
mounting plate. Four flat pins on the plate mate with
the pack. I noticed during the installation that the four
were chromium plated. This is one of the worst conceivable
plating materials for a low voltage connector, because chromium has a
habit of forming a tough non-conducting oxide layer on exposure to
air. Still, the connectors were doubled-up, two for (+) and two
for (-), and so I put my initial doubts aside and presumed that the
arrangement must be OK in practice. Using the battery upside
however, it transpires that the connector is not quite as fully
inserted as it would be with the assistance of gravity. The
situation might also arise if the battery were to be mounted
horizontally. This no doubt contributed to the problem that
emerged, for which the symptoms were: random loss of power, and random
down of the system. It was
initially difficult to identify the cause, and the misbehaviour grew
and soon made the bike unusable. Eventually I worked-out what
happening by running the bike on a bike-stand and measuring the supply
voltage at the input to the motor unit. Random shut-down was
caused by large fluctuations in the on-load voltage, and the fault
reproduced by rattling the battery pack up and down on its mounting
plate. Careful inspection then showed that one of the
been getting hot and had started to melt the surrounding plastic. Also,
the connections are doubled-up, this indicates that its
partner was barely working at all.
Mounting plate and battery pack,
with signs of connector overheating.
I might at that point have decided to demand a
replacement battery, but that would not have solved the problem of
having to use it upside down. Also, I do not think that the
connector is fit for purpose, even if it is used the right way up.
I therefore decided to forfeit the warranty and solve the
by modifying the battery pack. I did that by installing a
female XT60 connector, which, as the name implies, is rated for 60
A. XT60s have gold-plated solid copper pins and receptacles
with a high contact area, and so have extremely low resistance.
Note that carrying out modifications to a vehicle battery
pack carries a risk of fire or explosion, and is therefore a job for a
competent electrical technician (please also see my Disclaimer
Battery pack with XT60
wired across the existing connector.
A small circuit board can be purchased
for the XT60, enabling both the male or female types to be used as
bulkhead connectors. To prevent accidental short-circuits,
connectors on battery
packs must, of course, be female; so I fitted a board to a female
connector and mounted it on the battery case.
In doing that, I made a couple of pilot holes in the bottom
battery pack, and fashioned an XT60-shaped hole in the ABS using a
modeling knife and some small round and square rough-cut files.
When mounting the connector, I placed a couple of spacers on
the retaining screws, to minimise the protrusion, and sealed the
connector body into the hole I had made using architectural silicone.
I wired the XT60 directly across the existing connector,
thereby retaining the normal functionality (for what it's worth), and
also siliconed around the original connector to improve the
Finally, on reassembly, to minimise water ingress as far as
possible, I taped the join between the upper and lower parts of the ABS
housing. Note that it is possible to buy silicone rubber caps for female XT60
. These will exclude dirt and help to prevent
short-circuits in the event that the battery is stored or used on a
with the standard connector.
Having opened the battery pack, I had
an opportunity to make observations that would not otherwise have been
possible. I noticed that the On-Off switch is not capable of
handling the current required by the Bafang motor, and this function is
instead accomplished by using the switch to turn on a
transistor. Presumably, the cost of a small switch and a MOSFET is less
than that of a high-current switch. A somewhat worrying
feature however, is that plugging-in the charger also switches-on the
battery output, which is how the press-button battery-level indicator
comes to work either
when the battery is on, or
when the charger is in. This means that charging the battery while it
is installed on the bike has the effect of turning it on. The
bike, of course, does not wake-up unless the handlebar power button is
but it means that the the motor will not go to sleep straight away if
the charger is plugged-in before the battery is turned off.
Whether this is a serious issue is moot, but it is not ideal.
"Off" should mean "Off".
The appalling chromium connector
seriously coloured my initial impressions of riding the
bike. I came to the (very-pessimistic) conclusion that the
makes a rather feeble contribution to the rider's efforts, and while it
did (initially) enable me to get up the hill from Ottery without
stopping, I still had to do quite a lot of work. I also noted
that, while the twist throttle could start the bike from standstill on
level ground, it could not do so on a 5% gradient. The effect
of fitting the XT60 connector, and thereby discovering the actual
the motor, was consequently astonishing.
Although the following calculation
conjecture, we can easily get a rough idea of just how deleterious the
original connector was. If the Bafang BBS01 were to have a
peak power consumption of 250 W at 36 V, it would require a current
of 6.9 A. In reality however, if it is to deliver
W to the road, it needs a somewhat greater input than that,
probably approaching 300 W. This means that we should expect
typical peak current of about 8.3 A, or say 8 A in round numbers.
Hence, in the state of maximum demand, the motor looks something like a
36/8 = 4.5 Ω resistance.
Now, if the connector were to have a
resistance in the region
of 1 - 2 Ω, then at times of peak power demand, it would be
expected to cause a voltage drop of between about 6.5 and 11 V.
Instead of a nominal 8×36 = 288 W input to the
motor, we would have
= 193 W and (36-11)2
= 139 W.
Approximately halving the motor power would indeed result in
performance, and the reduced voltage is likely to cause the controller
to assume the battery to be
dead and switch off.
When I built my second e-bike, I bought
model of battery again but fitted an XT60 connector immediately.
Bike performance with
(44T with 9sp
12-36T cassette, 27.5" wheels
The gearing configuration I adopted initially for road use was a 44T
front chainwheel with a 12-36T 9-speed rear cassette. This
turned out to be an acceptable combination for town
and country cycling, giving speeds in the range of 6 to 20 mph in
gears 3 - 7, the ability to reach 25 - 30 mph in gear 9, and the
ability to pull away on the hand throttle on uphill gradients a little
in excess of 10% in gear 1.
Bafang dished chainwheel gave a chainline exactly parallel to the
frame-line in gear 5, which is ideal. Dérailleur changes
smooth, provided that the drive was slackened-off a little (just
as in normal cycling); and there seemed to be no real need for
sensing system provided with some of the more exotic versions of the
In order to understand the
assistance, it is useful to be aware that a normal cyclist (i.e.,
someone who is not an athlete) can produce an output of 100 - 200 Watts
for fairly long periods, and an output of 400 - 500 W in short bursts
for going up hills or hard acceleration. An additional 250 W
the electric motor therefore makes climbing hills seem like traveling
on the flat. In my case, having limited cardiac output, I can
happily produce the 100 - 200 W needed for prolonged periods of level
cycling, but the 400 -
500 W needed for steep hills is beyond me. Add the 250 W from
BBS01, and I get 450 W, which means that typical road hills no longer
present a problem. If I pedal moderately hard, I find I can
up the 5% (average) hill from Ottery to my house at around 11 mph in
gears 3 - 5, without any need to take a rest. I also found
could get up the hill on the throttle, without any pedaling at all, at
around 6 mph in gear 1. It is of course tedious to go
slowly on a paved road, but it does give me the reassurance that I can
still make it
home even when I am completely exhausted. Incidentally, the
that it is fun to pedal within the physical capabilities of the rider
makes using the e-bike into an excellent form of exercise.
The way in which the motor unit
to the rider is initially somewhat strange, but getting used to it is
not difficult. As set-up for use on British roads
(assistance stops at 15.6 mph), motor output is at its greatest when
rider pedals slowly, and decreases progressively as the speed climbs
towards the assistance limit. This gives the curious effect
assistance can be increased by changing up when going uphill. The
provision of a freewheel ratchet in the motor unit also permits what I
'faux pedaling', which is where the act of turning the pedals too
slowly to lock the ratchet and propel the bike, causes the motor to
propel the bike instead. This gives onlookers the false impression that
you are doing some work, even though you are actually getting a
completely free ride.
I have so far not managed to exhaust
the battery before recharging it;
but with moderate pedaling, I would estimate the range to be in the
region of 40 to 60 miles.
ratio gearing using small front chainwheel
(32T with 9sp 12-36T
cassette, 27.5" wheels
For my first hill-climbing and off-road cycling experiments, I fitted a
intermediate front sprocket to a 104 mm BCD spider adapter from
RisunMotor (also avalable from Hallomotor and ConhisMotor).
Strictly, the spider was designed for chainwheels
34T and greater, but being made from hard stainless steel, it was
possible to grind it down (using an ordinary workshop tool grinder)
until it just cleared the chain on a
After-market spiders with 104 mm BCD are available for the
Here, a Shimano 32T intermediate front sprocket is
attached to a Hallomotor stainless steel spider adapter. A
spacer of about
mm is required to prevent the
chainwheel bolts from rubbing on the motor housing. The
spacer is easily made
from a piece of 20 SWG aluminium sheet (starting by laying the spider
on top and marking the holes with a scriber).
Here a 32T Shimano sprocket is mounted on an aluminium
104BCD spider. As is the case with the steel spider, this one
is intended for sprockets of 34T and larger, and so requires some
filing to make it clear the chain (do not try to shape aluminium using
workshop grinder, it will clog the stone). A 0.9 mm
spacer is required between the hub and the spider, as for the steel
The 32T front sprocket fitted to a bike
with a 12-36 cassette gives a lowest
32/36 = 0.89 turns of the back wheel per turn of the crank.
very roughly the same as changing down by a further two gears relative
to the ratios available with the 44T front sprocket. It gives
bike with 27.5" wheels the ability to pull-away uphill on the throttle
on a 20% gradient
The disadvantage of the small front
that it lacks the dish-shape of the standard Bafang sprocket and so
gives the best chain-line in gears 7 and 8. The Shimano
however have a tooth profile and shifting ramps that permit
them to be used
with a fairly severe degree of misalignment, and this allows the lowest
ratio to be used reasonaly successfully. One downside is
that the chain tends to climb down the cassette if the bike is wheeled
backwards in gears 1 or 2. That situation is usually
however, because gear 3 is about the same as the lowest required road
ratio. Fortunately, the additional freewheel hub in the Bafang motor
prevents chain climb-down on backpedaling. Critical setting of the
dérailleur adjustments is necessary to avoid clicking
and grumbling when climbing very steep gradients, and the drive sounds
noisy under high loads. Fairly rapid wear is to be expected.
Overall, the 32T front chainwheel is
for use on the ordinary roads.
downhill, it is impossible to pedal fast enough to catch-up with it,
even in gear 9; so freewheeling is the order of the day. Going uphill,
there is not much cause to use the lower ratios, but
the bike in this configuration is nevertheless serviceable if somewhat
From an engineering point of view, I
must also say that I hated the
arrangement and could not wait to get rid of it.
The drivetrain sounded very unhappy in the lowest
ratios, and I did not fancy the idea of going too far away from home.
(42T with 9sp 12-36T
cassette, 27.5" wheels
The narrow-wide chainring is a wonderful invention; and once you
what it is, it is difficult not to want one. Since normal
have alternating inner and outer links, and must have the same
number of each (provided that there are no half-links); a chainwheel
can have alternating wide and narrow
teeth, provided that the total number of teeth is even. This gives a
dramatic increase in the strength of the sprocket for a given material
type, allowing hard aluminium alloys to out-perform steel. This profile
cannot be used for the cogs in dérallieur changer
the wide and narrow teeth must be matched respectively with outer and
inner links before the chain will drop into place. It is however still
possible to re-fit a chain on a narrow-wide sprocket in pitch darkness,
it won't go on unless
is properly positioned.
Strength is also not the only
or even the main advantage. The chain mates perfectly with
narrow-wide structure, and this reduces the side-to side movements
that cause noise and wear and can sometimes trigger the chain to jump
when going over rough ground. Hence, the N-W profile is
becoming increasingly common on the front chainwheel of
high-performance 1×N drivetrains.
When fitting a narrow-wide chainwheel,
note that while there should
no half-links in a system having a tension arm, it is
important to be sure that there definitely aren't. Also, conversely, if
you decide to use a narrow-wide chainwheel in a single-speed system or
a system having hub
gears, you might need to use a tension arm in order to establish the
correct chain length without using a half-link.
of the PreciAlps chainwheel is deeper than that of the ones supplied by
Bafang, and I when I bolted it directly on to the motor on the
Sterndale I found that
the teeth rubbed on the bike frame. To overcome that problem, I
included one of the 0.9 mm spacers that I had made previously, as can
be seen by careful inspection of the photograph above. It would be
useful if manufacturers would recognise the importance of having such
shims available, even if they are not always necessary. When I later
fitted a PreciAlps 42T N-W to the Saracen 29, it did not need a
Relative to the smallest dished Bafang
(44T), the 42T PreciAlps gives a 4.8% increase in mechanical advantage.
This makes it slightly easier to get up steep hills, without
sigificantly compromising top speed. What was most noticeable however,
was the smoothness and lack of noise from the drivetrain (particularly
in comparison to the non-dished 32T front chainwheel that I had just
replaced). Such clean performance is representative of a reduction in
drivetrain energy loss, and a concomitant reduction in wear. My
appraisal of the 42T N-W promptly caused me to lose interest in all
other front chainwheel options; and so I e-mailed PreciAlps to confirm
that it would work with an
11-speed chain, and then ordered another for the Saracen 29.
As a test of 42T chainwheel on the 700c
I rode up a hill out of Ottery St Mary known as the Chineway.
This is on the Tour of Britain cycle route; and has an
gradient of 20% (1/5) for about 1 km, thereby providing one of the more
challenging hills for the competitors. I found that I could get up the
worst parts of the hill at 5 mph (8 km/h) in bottom gear without any
need for rest. The trick was to hold the hand throttle fully open and
pedal moderately hard, but there was no great difficulty. I then turned
right onto a road called 'Hemmings Lane', which leads to my next-door
neighbour's farm (where I can cut through). This has a section of about
50 m at the beginning, with a gradient of 25% (1/4). There I did have
to work hard, but there was no need to stand up in the pedals; and it
was clear that the drivetrain configuration was good for some fairly
The advantage of the hand throttle when
steep hills is not that the such hills would otherwise be impossible,
but that the magnet on the rear-wheel must pass the sensor at least
twice before the motor unit can determine that the rider needs extra
assistance. Thus the throttle can tell the controller that maximum
power is needed immediately, and there is then no delay while the
system determines that the bike is nearly at a standstill in bottom
gear. This shortcoming of systems not having a hand throttle is, of
course, the reason why expensive commercial e-bike offerings have an
additional sensor to inform the controller of the chosen gear ratio.
Another solution would be to fit more magnets to the back-wheel spokes
and change the speed-calculation algorithm accordingly.
(42T with 9sp 12-36T
cassette, 29" wheels
Once I had the Sterndale working well, I set about converting the
Saracen 29. Although I was planning to fit an
11-speed rear dérailleur eventually; I got it going with the
existing 12-36T 9-speed cassette and shifter in order to avoid
implementing too many changes at once. I then went out riding on it,
with my son Steve on the Sterndale as my companion.
As mentioned previously, a bike with
has 5.4% mechanical advantage over one with 29" wheels. The
drivetrains on our bikes were otherwise identical. Thus Steve had a
small advantage over me, and I am, by far, the most frail.
we were both able to ascend a 21% (1/4.8) gradient of about 200 m with
some fairly hard pedaling but no great difficulty. I would, of course,
have preferred not to have lost the mechanical advantage provided by
the smaller wheels of the Sterndale; but being able to manage
a 1/5 hill is probably an acceptable limit for many people.
(42T preci-alps with
11-46T casette, 29" wheels
Modern bikes are moving to a single front chainwheel configuration as
rear dérailleur designs improve. This development
offers the possibility of both road and off-road capability just by
moving the shift lever. To me, this seemed a little too good to
be true; but my e-bike research could not have been complete
without at least trying it. I therefore decided to fit a Shimano 11-46T
Deore XT drivetrain to the Saracen 29 (the Sterndale 700c having, by
that time, become my primary means of transport). Even wider-range
options exist, but I
was initially sceptical that such cassettes could be made to work
without frequent critical adjustment, and the ratios given by the XT
11-46T covered a range I had
already evaluated (by changing front chainwheels) and found to be
Shimano 11-speed 11-46T cassette with
long-cage dérailleur. The drivetrain is shown in
ratio setting, so that the tension pulley (lower) is at its
forward. The chain slack is just sufficient with 118 links. The
supplied B adjustment screw is fully in, but there was no need to fit a
longer one. The front chainwheel is a PreciAlps 42T narrow-wide.
In order to carry out the conversion I purchased the following parts:
Shimano XT CS-M8000 11-46T 11-speed cassette.
Shimano XT RD-M8000 11-speeed dérailleur, Shadow
SGS (long cage).
Shimano XT SL-M8000 11-speed RH bar mount
shifter with visual display.
KMC X11.93 11-speed
chain with 118 links.
links (the chain comes with a single-use link).
Tools needed for
fitting were allen keys, Bowden cable cutters, and a
carpenter's scratch awl (i.e., a tapered spike) for opening-up
the cut end of the shifter cable
The XT 11-speed cassette can be
retro-fitted to an existing
Shimano-type freewheel hub, and so it dropped straight onto the splines
vacated by the previous 9-speed assembly. The tooth sequence
is 11-13-15-17-19-21-24-28-32-37-46, giving an interval sequence of
2-2-2-2-2-3-4-4-5-9. The increasing interval is normal, the point being
usually to maintain a crudely equal percentage difference, but in this
case there is a very large jump from 37T to 46T.
The 11-speed shifter was the rear bar
supposedly for the right-hand handlebar, but it fitted perfectly well
on the left and permitted a good control position relative to the brake
lever. Furthermore, there are no numbers on the indicator,
the legends (Shimano, Deore XT, Dyna-Sys II) are orientated so that
they are the right way up for the rider to read. Consequently, the
control looks as though it should be on the left anyway, and the
indicator moves from left to right on changing to a higher gear.
The shifter came packaged with the
cable inner already fitted, and a spare cable outer (including plastic
frerrules) placed in the box. I particularly needed a new cable outer
because the old arrangement on the Saracen used frame lugs and had bare
sections. A continuous run allows the cable to be routed away
from the point on the top frame tube where a bike stand needs to be
clamped during setting-up. I was advised by the supplier that I would
have to purchase the outer separately, but that information was
For the Shimano XT M8000 Shadow+
dérailleur, it is not necessarily clear from the sales
literature that it will work with an 11-46T cassette. Chain Reaction
from whom I bought the parts, however assured me that it would; and
confirmed my surmise that I would need the long-cage version.. The
dérailleur is provided with a chain stabiliser, this being a
unidirectional friction-clutch mechanism that prevents wild oscillation
of the chain and cage on rough ground. A switch is provided so that the
clutch can be disabled during wheel changing, making the cage easier to
move by hand.
The longest available 11-speed chain I
had 118 links. This turned out to be just about right with a 42T
front chainwheel, but I am not sure that anything significantly larger
could have been accommodated. For the Saracen 29, the distance from the
crank axis to the back-axle centre-line is 443 mm. For bikes
smaller wheels, this distance might be reduced, possibly allowing for a
larger front or back sprocket; but other considerations dictate that
the shortening of the bike will not be equal to the reduction in wheel
radius. For the Sterndale 27.5", for example, the distance is 432 mm
(11 mm shorter then the Saracen), whereas the reduction in radius is 19
Fully expecting that the setting-up
be tricky, I was rather surprised by the ease of commissioning. Since I
did not have
a large-enough spoke guard for the cassette (the plastic disk that goes
between the inner sprocket and the spokes), I set the lower limit (L)
to align the jockey pulley centre line just slightly outboard of the
large sprocket centre line (away from the spokes). This is actually
standard procedure, but if there is a spoke guard, it can be tempting
to tweak the L adjustment for best pick-up. Next I pulled
the dérailleur out by hand and aligned the jockey
line to the smallest sprocket centre line using the upper
After that, I fitted the chain and adjusted the B screw to get
clearance between the large sprocket and the jockey wheel in the lowest
gear. I had to turn the B screw to be pretty-nearly fully in, but I did
not need a longer one. Finally, I adjusted the cable tension by turning
the barrel adjuster
on the shifter (having already pulled the cable tight through the
anchor point during assembly), to get correct chain alignment in the
middle of the gear range.
To test what I had done, I ran the bike
the hand throttle while shifting up and down through the gears. I fully
expected that I would need to carry out a lot of critical tweaking, but
the system worked flawlessly from the outset, like no other
dérailleur I had ever messed-with before. That might have
luck, of course; but I suspect that it might also be associated with
the rather elaborate pick-up ramps machined into the face of the
large sprocket. The unhesitant, serpent-like, climb from 37T to 46T is
something to behold.
For road testing, I went for a few
short rides to
check that everything was bolted-on correctly, and then set out in
search of steep hills. The drivetrain, as might be expected by now,
performed perfectly, and I found that hills that I had previously
regarded as too steep, were now easy to tackle using the 46T gear. Thus
I found I could manage a 25% gradient with a little pedaling but no
real stress, and I could pull-away from standstill using the
hand-throttle on a gradient of 20% (as was the case with the earlier
unsatisfactory 32/36 flat front-chainwheel experiment). I would have
preferred a smaller
gap between the first and second gears, but this was not really a
problem; and I could see the logic of having a 10-speed road set plus
an extra low ratio.
Gear changes were so smooth that, if I
the power, there was often no audible indication that the
shift had taken place. This was a little disconcerting at first,
because I wanted to be sure that the dérailleur had operated
correctly, but I quickly learned to verify shifting via the change in
A feature of the shifting mechanism
that I found particularly helpful is
that it allows for a downshift of up to 3 sprockets at a time, e.g., 11
to 8, 8
to 5, etc.. This allows the bike to be changed rapidly into low gear,
often with only one front chainwheel rotation to complete a multiple
is extremely useful for going from downhhill to flat, or from
downhill to uphill, or for giving-way to inconsiderate drivers.
Having gained confidence that I could
about any paved surface that the Honiton Forest could put in my way, I
kicked the bike off the road and headed up the Knightstone bridleway,
which is located just under a km from my house. This heads up to a
single-track road known as the Higher East Hill Strips, in the East
of Outstanding Natural Beauty (AONB). The terrain of the bridleway
consists of rain gulleys, scree slopes, and paths covered in
leaf-litter, some of it adjacent to some rather scary drop-offs. On the
shortest route between the Middle Strips (where my house lies) and the
Higher Strips, the gradient is variable between about 20% and 33%. To
navigate it safely on the 'easy slopes', I often needed to put my feet
ground, but I was perfectly able to do that by keeping the bike going
on the throttle. In fact, my biggest worry was that going at about 5
mph was often too fast to allow me to choose the best course through
wheel-ruts and gulleys. On the steeper scree slopes however, I decided
not to risk
bursting the tyres by having my weight on the saddle, and the solution
was to get off and crack the throttle open a small amount; in which
case the bike would drag me up the slope like some kind of demented
Riding the upgraded Saracen both on and
was, of couse, enormous fun; and it quickly dawned on me that it
had given me the freedom to go just about anywhere. It is perhaps not
the case that everyone will need such extreme versatility, but it is
surely worth knowing that modern engineering permits it.
Sunrace MS8 EAZ 11-46T
(42T preci-alps with
11-46T casette, 27.5" wheels
For the Sterndale 700c, the axial distance from the back wheel to the
crank is 432 mm. This measurement told me that the Sterndale with a
PreciAlps 42T would also work with a 46T cassette and an XT M8000
11-speed mechanism. I therefore bought another
dérailleur, shifter, and chain, the same as for the Saracen
but this time I opted for the Sunrace MS8 EAZ 11-46T cassette. The EAZ
sprocket sequence is 11-13-15-18-21-24-28-32-36-40-46. This gives an
interval sequence of 2-2-3-3-3-4-4-4-4-6, which is much more evenly
spaced than that of the Shimano 11-46T. Sunrace also make an 11-50T
cassette, MX80 EA5; but my experience seemed to suggest that a 46T
bottom gear is adequate for an e-bike, and although Sunrace cassettes
are Shimano compatible, there was the possibility of difficulties in
setting-up with a 9% larger cassette.
>> more to come:
Confucius loop handlebars
compass friendly 6061 Al.
Stainless A4 is austenitic - compass safe.
Electric bikes, 2016 UK legal
EAPCs in the UK (excluding Northern Ireland) are limited to a maximum
assisted speed of 15.6 mph (25
km/h), a maximum motor power of 250 W, and must have pedals that can be
used for propulsion. The bike can go faster than 25 km/h, but
only under power provided by the rider. Failure to comply
with these rules causes the bike to be classified as a motorcycle;
which requires registration, an MOT certificate, tax, insurance, an
approved helmet and a
license. Non compliance is therefore a serious offence and
can lead to a heavy fine and a general driving ban. In the
event that some idiot knocks you off your bike, it might also
compromise your ability to claim compensation.
& Go - self conversion type approval exemption
The DFT rules state that an EAPC with a Twist & Go facility,
i.e., the ability to move under electrical power at speeds up to 15.6
mph without pedaling, requires type approval. The reason for
the requirement is that the motor does not necessarily cut off when the
rider stops pedaling. This seems to cause a problem for
people who want to convert existing bikes, but the link above relates
to a clarification. The DFT recognises that Twist &
Go is an important improvement for people with limited physical
abilities, and the Type Approval requirement is strictly directed at
manufacturers. If an existing bike that has already been used
as a pedal cycle on public roads is converted for electrical assist,
the fitting of a
Twist & Go control does not constitute an offence.
Highway Code (UK)
Rules for cyclists.
Sections 59 - 82
Some of the rules are legal requirements (e.g., you MUST
brakes and use lights at night, you MUST
obey all traffic signs), but many are advisory (e.g., you should
type-approved helmet, etc.).
It is however unlikely that you will win a legal dispute if you have
not followed the advice given (see also: Darwin Awards
Future legal changes
There are pressures within the EC to require e-bike users to have
party insurance. There will no doubt be much wrangling over this issue
in the months and years to come; but to the author's mind this is not
an entirely bad idea provided that the costs to the rider reflect the
actual risks. UK rules might also diverge from EC rules at some point
Note that an M-Drive kit does not usually include a battery; the latter
because there are choices of capacity. The Bafang BBS01 and
clones are sold with a thumb throttle, usually said to be for off-road
use only, but see the Twist & Go type approval exemption info
above. There are also ½-twist throttles available for those
who are used to riding a motorcycle. Some motorcycle
have an adjustable friction pad, to allow hand signals with power on,
but an e-bike throttle should spring-back when released.
sales UK - Bafang BBS01 Conversion kit with 44T chainwheel
MAF Scooters - Bafang BBS01 with 46T chainwheel
Classified on the website under > Parts > Electric Motors.
Bikes - Panda M-Drive 36 V 250 W kit
clone, 48T chainwheel).
Whoosh Bikes - Bafang BBS01 with
Bikes - Bafang BBS01 with 46T chainwheel
Pedalease - TLH 36 V 15,6 Ah
Li-ion battery packs.
Good source of information as well as parts. Good
advice on how to use the BBS01
BBS01 Kit, product manuals, Bafang
BBS brake sensor
, spider adapters allowing the
use of non-Bafang chainrings (see Bafang/8Fun spares).
Bafang uses Higo Mini B series connectors
between the motor unit and the console and various controls. For info
and purchase of additional connectors see:
France. Mid drive parts and accessories, lightweight
spiders for the BBS01/02. 42T is
the smallest possible front sprocket size that allows the optimum
(i.e., a dished chainwheel). PreciAlps front chainwheels use the
narrow-wide tooth profile. The company also makes a 42T extension
Note that chainwheels for
the BBSHD (1 kW) M-drive do
the BBS01/02. The sprockets look similar
in photographs, but the ones for the high-power drive are smaller and
have a smaller BCD for the 5 mounting holes.
(Shanghai). Spider adapter, etc.
The perfect solution for adding extra accessories (smartphone / GPS
holder, action camera, headlight) once the e-bike conversion has used
up all of the handlebar space.
Don't forget to have
a look on ebay
There's plenty there, including batteries, Bafang-fitting
spider adapters, bashguards, cassettes, twist
throttles, brake sensors, bike tools (and lots of other stuff you
want). Note however that it may be cheaper to buy expensive
items directly from the supplier.
Soanes Cycles, Colyton, Devon
Long established Devon bike shop with a reputation for good
deals and good service. The author's preferred local cycle
shop, not an e-bike supplier.
Information and review
Manuals are available from most of the conversion kit suppliers (see
above). Some are better than others. Read them.
ebike - Installing the Bafang 8Fun BBS01
Dave Atkinson - Installing the Panda M-Drive
Dave Atkinson - Panda M-Drive kit
The reviewer lives in Bath, and needs to climb Lansdown Hill every day
to get home from his office. He finds that the supplied 48T
chainwheel far too big when used with his 11-28 cassette and suggests
that the ideal chainwheel size for his bike
would be in the 34 - 42T range. It depends on the rear
ratios and the wheel diameter of course, but commentators seem to agree
that 48T gives
self-powered top speeds that you just don't need (~ 50 km/h / 31 mph),
and this should be traded for torque at the bottom end.
UK (the CTC), Richard Hallett - Panda M-Drive kit
Discussion of powered wheel and friction drive options, plus
review of the Panda M-Drive and its installation process.
some derailing problems due to poor chain line. Also finds
give too high a top gear (with an 11T rear), and suggests that 45T
would be better (note
that Bafang makes a 44T chainwheel for the 8Fun). You can
get up a 1/10 hill fairly easily with the 48T front sprocket, but the
manage very steep hills will be improved with a smaller one.
- Charging Lithium Ion batteries.
to e-bike battery connectors
A measure of the gradient on which the bike can pull
away under its own power is extremely useful when experimenting with
sprocket ratios. This Sun
bike inclinometer consists of steel ball
in a curved tube filled with viscous liquid, and has scales in gradient
% and degrees. - Simple but effective.
happy to do the installation yourself, chances are you'll already have
many general workshop tools at your disposal (i.e., socket
spanners, adjustable wrench, copper or plastic mallet, G-clamp, bench
grinder, Allen keys,
screwdrivers, easing oil, Loctite blue, cable ties, etc.).
You'll probably also have a set of tyre levers. In
case, the following additional tools will provide the capability to do
general bike servicing. You probably won't need all of them for an
M-drive conversion; but if you're going to
start comprehensively dismantling bikes and messing around with
sprocket ratios, it's best to be equipped for
The individual items are not expensive,
can get most of them on ebay (if you search for
these items online, put "bike" into the search term). Note
that some of the
tools shown below are for the amateur market, and will not
industrial use; but they should do the job if applied correctly and not
subjected to excessive force.
chain wrench (sprocket wrench with hook wrench and
The spline wrench fits the Bafang outer aluminium
bottom bracket nut. The chain wrench is used for holding the rear
sprocket cassette still while undoing the retaining nut.
19 - 51mm size is required for the Bafang
bracket castle nut. A cheap multi-purpose wrench is not
good enough for the job.
puller (for removing pedals).
The basic tool is
used for square taper spindles. Shimano Octalink
(8 spline) and Isis (10 spline) crank arms
require an additional anvil piece that fits into the end of the shaft
||Octalink / Isis adapter.
For removing splined cranks when using a puller
designed for square taper cranks.
Left: magnetic type, snaps onto the end of the puller; Right:
bracket disassembly tool (20 spline). The
chainwheel side bottom bracket retainer nut has a left-hand thread.
To loosen the nut, hold the tool in place with a G-clamp,
with a piece of wood to protect the paint on the other side of the
bracket. A sharp (but not particularly hard) tap on the
wrench with a soft mallet should get the nut turning.
Used for adjusting the end-play of tapered axle
Used for detaching the cassette hub (Shimano / SRAM
Needed if you want to replace worn cogs or change the rear
dérailleur ratios. The
outer nut fits into a 24mm or 15/16" socket wrench.
||Chain rivet extractor.
A general necessity in any bike toolkit. Needed
for removing the front dérailleur
fitted. Needed for shortening chains, etc.
Convenient for rejoining chains, and more reliable
practice of pushing pins back in. Make sure you get the right
width for your rear cassette (8, 9, 10, 11 speed, etc.).
||Quick link pliers.
Some quick-link pliers can only open the link
(i.e., pull the
rollers together). You might as well get one that can also
close it (i.e., pull rollers apart), although a sharp tug on the chain
works just as well.
||Chainring nut wrench
For tightening the fasteners that attach the
front chainring to the
spider. This one (Shimano TL-FC21) also has a crank cap
and 9 and 10 mm wrenches.
||T-handled chainring nut wrench.
Allows more torque than the flat peg spanner, but
can only be used when the chainwheel is off the bike.
wrench / spoke key (for 10 - 15 gauge spoke nipples).
needed for M-Drive conversion, but used for general wheel tuning.
||Bike stand (30
Once you have fitted the Bafang display to the
handlebars, you can no longer turn the bike upside down for servicing.
A stand is also convenient for making electrical measurements
setting up the dérailleur (etc.). A 30 kg rated
had for about £25.
Satra S-T300W ½" beam
type (shown) is ideal for tightening crank bolts, inexpensive
(£12.50), and refreshingly
free from scales calibrated in furlong firkins or other non-SI
Allen key bit socket (½" square drive)
For tightening the pedal crank bolts (socket sets
often include this item).
|Ratchet Adaptor / Adapter.
Converts torque wrench or breaker bar into a ratchet
drive. The amount
of torque that can be transmitted must be stated by the manufacturer
(if it isn't, you don't want it). Sealey AK737 ½"
sq. drive (shown) withstands up to 512 nM. Sealey AK7371
withstand up to 1412 Nm.
||Steel wire / bike cable cutter.
||Carpenter's scratch awl.
A tapered spike for opening-out the
cut ends of Bowden cable outers.
Scale divisions in mm
quartz shard, about 8.5 mm in length managed to insert itself
point-first into the rear tyre of the Sterndale. The bike was
wheeled home, and the puncture in the inner tube located.
Then the tyre was carefully searched for penetrating objects
the vicinity of the puncture. The problem here is that the
moves relative to the inner tube while the bike is being pushed. Hence
the shard was not found immediately and caused two more punctures
before it was finally located. A throrugh search of the tyre surface is
evidently a good idea when fixing punctures.
Throughout this article, the ratio changing mechanism has been referred
to as a 'dérailleur'. You don't need the acute accent in
English, but it is nice to remember that the device was popularised by
the French cycling enthusiast and journalist Paul de Vivie. There is,
nowadays, a tendency to refer to it as a
'derailer'; but a derailer is a terrorist who sneaks onto railway lines
in the dead of night and drags blocks of concrete into the track.
Derailers are horrid, whereas dérailleurs
have helped to make cycling into an effective form of transport.