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Written by: Peter Ballard
REFERS TO SINGLE WHEEL DRIVE UK SETUP. (RHD, CHAIR ON LEFT - ALL
DIMENSIONS INCHES
At constant speed on
a normally cambered road (slopes a little down to the left) the outfit
should pull straight at constant speed. If not, it can be adjusted to do
so, but it will take you quite a few iterations until you get it to your
satisfaction.
THERE ARE TWO
MAJOR ADJUSTMENTS
Sidecar wheel toe-in
- the sidecar wheel should not be parallel to the bike track, but it
should try to follow a path that would converge on the path of the bike
if rolled forwards. The toe-in of the sidecar wheel will push the outfit
to the right. The toe-in is usually measured over the length of the
bike; so if you get two long straight planks of wood and push one
against the outside of the bike tyres and the other flush against the
outside of the sidecar tyre (on two bricks often helps this) then the
difference in distance between the planks measured at the rear wheel and
the front wheel will be the toe-in. But there are various controls and
limits on this:
Ø As
the lead of the sidecar wheel over the rear wheel increases, the effect
of toe-in increases. However this 'lead' is not usually adjustable, it
is certainly fixed on all Russian St Ukrainian chairs (unless you want
to cut and weld). A short lead of 6" will tend to cause the rear wheel
to lift (dangerous) on right-handers under deceleration. A large lead of
18" will cause sidecar wheel scrub at slow speeds in either direction. A
lead of 9" to 12" is normal and a good compromise.
Ø A
big diameter sidecar wheel (18" or 19") will result in a bigger contact
patch for the tyre and thus the tyre will provide more 'push' if toed-in
compared with a small (8" or 10") wheel (of similar tyre widths).
Ø As
the sidecar wheel toe-in is increased over a certain amount, the sidecar
wheel drag and tyre wear starts to increase and negates any expected
beneficial effect of toe-in. A heavy chair will make any toe-in more
effective, which more or less compensates for the chair being heavy.
Range of toe-in adjustment - big wheels from 1" to 2", small wheels from
1" to 3".
Bike lean-out - away
from the sidecar. Lean-out is measured with the outfit normally laden,
including people. Lean-out results in the bike trying to turn right away
from the chair, thus counteracting the pull of the chair that would make
the outfit turn left. But again there are various controls and limits on
this.
Ø Lean-out
is of most effect if the steering trail (see below) is large, which is
unfortunate since we also strive for a short steering trail.
Ø If
the chair is light and the bike is heavy, then more bike lean-out will
increase the likelihood of the sidecar wheel lifting on left-handers.
Thus with this combination use more sidecar lead and less lean-out.
Range of bike lean-out usually from zero to 3 degrees, but 5 degrees
absolute max.
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RECOMMENDATIONS
Big bike with light chair -
Go for max sidecar lead, max toe-in, only then try lean out from
vertical - minimises lift of sidecar on left-handers.
Bike with heavy chair - Go
for average lead, max lean out and average toe-in - minimises sidecar
tyre scrub and drag.
Definition - Steering Trail
- the distance on the ground between where the steering axis hits the
ground and the centre of the front tyre contact patch. Noting that the
contact patch centroid (or centre of area) moves rearwards as speed
increases.
Sidecar Fork Trail -
Measured with the outfit laden - sidecar fork trail is typically 1/2" to
2".
Solo Trail - typically 3" to
6" to give handling characteristics required:
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NOTES WITH RESPECT TO VARYING LOADS ON THE OUTFIT
If you carry a pillion this will
depress the bike's rear suspension and will make the bike lean out
more, thus pulling away from the chair.
If you load up the sidecar this
will mainly depress the sidecar suspension and reduce the bike
lean-out, but will make any sidecar wheel toe-in more effective.
With an unsprung sidecar wheel
(like in the old days when the body was sprung on the chassis) then
weight in the sidecar will only depress the bike rear suspension,
resulting in less pull to the left. |
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