Pedal bike and e-bike stability,
and the need for a steering damper
Sport and off-road motorcycles often have a hydraulic steering damper
to inhibit uncontrolled displacement or oscillation of the handlebars.
The need for such a device arises because of a terrifying situation
that sometimes occurs with high-performance
machines. This is known as a 'Tank
Slapper' or 'Speed Wobble'. It involves an uncontrollable side to side
the steering, driven by the transfer of energy from forward motion.
The hydraulic damper
limits the rate at which the steering can change direction, essentially
acting as a low-pass filter to inhibit the troublesome energy transfer
obvious, is that light 2-wheeled vehicles, such as ordinary pedal bikes
and e-bikes, can also have severe stability problems in a variety of
situations. Those situations can be outlined as follows:
1) Needing to let go of
, e.g., to make hand signals
(particularly on poorly maintained roads in traffic).
Many cyclists seem to solve this
problem by not giving signals,
but the 'keep 'em guessing' approach is not necessarily an optimal
For an e-bike with its large battery, the problem can be
by providing motorcycle-type lighting equipment, particulaly traffic
indicators, a brake light, and a headlamp flasher (see e-bike
lighting and electrics
), but given that few will
adopt such an approach, matters can be improved by making the steering
2) Being forced
into pot-holed or rutted parts of the road
car and van
3) When riding with
heavily loaded panniers, bags, or a basket
4) Transient loss of
front wheel grip
(wheelies and skids, too much
weight over the back axle).
5) Going fast
(25 - 40 mph, 40 - 64 km/h) and unexpectedly
encountering rough surfaces, stones and rubbish.
6) Going off road
It is desirable to solve these problems or, in the immortal words of
"One day you'll be in the ditch, flies buzzing around your eyes, blood
on your saddle."
In addition to the problem of external
forces suddenly displacing the
handlebars, bikes have a serious ergonomic flaw, which is the way
in which the steering flops from side to side when the rider attempts
to park or manoevre. A full ±90º motion
of the bars
is desirable when turning the bike in confined spaces while dismounted,
but the tendancy of the steering to go straight to one extreme or the
other when released is problematic. Particularly, the simple
of leaning the bike against a wall can result in it folding-up and
falling-over as soon as the hands are removed from the grips.
There is at least one true hydraulic
steering damper for pedal
cycles, the hopey
but it costs around $200 + shipping. The hopey damper fits inside the
steering column. There are also devices, referred-to as 'steering
dampers' or 'limiters',
that provide a return spring intended to bias the steering
towards the centre position. Accessories of the latter type are the Hebie
limiter spring 695
(helical stainless steel) and the
handlebar limiter 696
The Hebie limiter system introduces the
idea of fitting a stabiliser on
the underside of the frame, underneath the tube from the steering
column to the
bottom bracket, leaving the top tube free. An independently engineered
version of such a damper might
include both a hydraulic piston and a spring, but it has the
disadvantage that many spring systems require a mudguard or
for attachment of a lug. In the event that no such
hole is available, an expanding nut inserted into the bottom of the
steering column is a potential solution, but it can be difficult to
get a sufficiently secure attachment. Certainly, there are
quality expanding nuts that simply do not work. Hebie however make
a Clamping Cone (Klemconus)
with a lug for a spring, to fit 20.5 to 25.8 mm i.d. steering columns,
and this works well.
The Klemconus is designed to anchor a spring on its own, but it might
also accommodate a
hydraulic damper if provided with an additional linkage.
The screw is M6, with a thread length of
45mm. Note that, in the mounting
instructions, the ribbed split-cylinder is called the 'adapter to
25.7mm.' The smaller split cone that engages with it is for 20.5mm ID
tubes or slightly larger.
For my own return-spring experiments, I
purchased a Klemconus and a Hebie 108mm 'replacement' damper spring
I did not use Hebie's own frame-tube
clamp and adjuster system because I wanted the option to try out some
kind of hydraulic damper at a later date. I therefore made
up an attachment out of a length of 8×16mm aluminium bar,
recessed 5mm screw holes so that it could be fixed to the under-frame
bottle-holder mounting sockets. The adjuster is a length of M8
stud, with one end ground down and drilled with an eyelet hole for the
spring. An M8 handwheel nut and washer, with plenty of silicone grease,
controls the spring tension. A length of translucent 10mm OD, 8mm ID
silicone tubing covers the stud and the spring.
Click on the
image to expand it in a new window
Parking with a stand, or by leaning the
against a wall, is greatly facilitated by using the Hebie limiter. The
picture below shows the attitude adopted when using a side stand. The
steering naturally turns slightly towards the direction of lean, but
there is no longer any need to take care in positioning the handlebars.
The particular concern in fitting a
is, of course, that it might adversely affect the handling; but this is
not the case. When riding at speed, large deflections of the handlebars
are not required, and the return force is not great enough to be
noticieable when both hands are taken off the grips. At low speeds
moreover, the centering force improves stability when giving hand
signals. It is fair to say, that on some badly maintained streets in
the author's home village, hand signals while in motion were almost
impossible before the damper was fitted. There was always the feeling
that the bike would fall over and be crushed by any vehicle following
it. With the damper installed, good long signals can be given with
ease. I am drawn to the conclusin that a spring damper should be
considered basic equipment.
I am interested in the possibility of fitting a hydraulic steering
damper, such as the type shown below:
This is a 330mm linear damper intended for use on motorcycles, with
stiffness adjustable by means of the knurled knob on the shaft end.
dampers are usually fitted asymmetrically, so that they
give about the same damping effect for any position of the
steering. I plan to use one symmetrically however. This means
that it will barely change length for small deflections of the
steering, and will apply progressively more damping as the deflection
It should be possible to fashion a new end-fitting
Klemconus, with an M8 socket, or perhaps a
choice of sockets at different radii, for the damper end bearing.
Actually, this new fitting will be better described as a bracket, since
it will need to be cranked up towards the bottom frame tube and then
bent back parallel, so that the damper will not get in the way of the
front suspension. Slippage of this bracket can be prevented by
having four threaded holes, two in front of the fork arch, and two
behind. Screws can then be put into these holes, and the threads
covered with silicone tubing to form anti-rotation pins.
would also like to retain the steering return spring. This
should be straightforward if I put a pin in roughly the position of the
original spring lug, and have the adjuster on a clamp around the body of
One difficulty I envisage is that of getting the
Klenconus out of the steering tube so that the modifications can be
carried out. The device is not as vicious as a star-nut, but it seems
unlikely that it will give up its tenure easily. It should be
reasonably straightforward however to tap the 20.5mm cone upwards from
below and thereby realease it from the 25.7mm adapter. It should then
be possible to tap the 25.7mm adapter out of the tube by passing a thin
rod down through the star nut at the top of the column.
To prevent it ever being necessary to remove the
Klemconus again, I plan to replace the M6 screw with a length of A4
studding and a nut. Bottom attachments can then be changed at will
without the nightmare of having to recapture the topmost threaded cone.
. . . . TBC
wobble - Wikipedia
Shimmy or speed wobble - Harris Cyclery
(Hebie steering damper kits and
(Hebie steering stabilizer
parts and kits).
(Search for 'Hebie'.)
Hydraulic damper 330mm
Hydraulic damper 330mm
(Ting Ting Car & Motor Store).