R60/2 with Globe GS200 and
Bathroom Scale under Sidecar Tire
Leaning left: 142
lbs
Sitting upright: 168
lbs
Off bike: 170
lbs
Leaning right: 200
lbs
Low speed wobble:
The sidecar tries to pull
the motorcycle to the right. Because of the lever action of the trail the
handlebars pull to the right. The propulsive force of the motorcycle tries to
straighten the handlebars. This tug of war continues until with the increase in
speed, the action of the propulsive force gains the upper hand.
Also "the steering of
almost every motorcycle with sidecar begins to oscillate at about 25 mph.
Because of this, a steering damper is required. There are motorcycles with
sidecars you cannot ride for more than 15 feet without a damper"
Factors that affect wobble:
Shock stiffness
Steering damper
Front wheel balance
Tire pressure
Swingarm bushing
Rigidity of sidecar
mountings and fittings
Sidecar position:
Moving sidecar forward will
cause pulling to right
Moving sidecar rearward will
cause pulling to left, hard to turn right and left and excessive tire wear.
From:
"Hal Kendall" <hal-kendall@w...>
Date:
Wed Jun 25, 2003 Subject:
Re:
[SCT] Re: Toe In and related topics
1.
There is NOT any single MAGIC number that will satisfy ALL bikes, sidecars,
situations,
2.
The range of generally acceptable values, including whatever H-D, BMW, and any
other manufacturer suggest, is a starting place. The final value is what works
for you, your driving style, the typical loading, the typical roads you drive
over, whether flat super slabs or highly crowned county roads. Most seem to try
for between 1/4 inch and 1-1/2 inches, or the equivalent in degrees if you have
a new computerized BEAR toe-in machine in your garage. Sorry, I did add one too
many zeros, it was near midnight when i posted. Say from 0.2 to 0.8 degrees.
3.
The easiest way to measure is to line up the center of the front and rear
wheels of your rig over a single straight painted line on the flat surface of a
clean double garage. This eliminates the problem of how to take the difference
in width of the front and rear tires into account. Make sure the front wheel is
lined up dead ahead. Take a straight plastic pipe, 4" diameter, lay this
alongside the sidecar tire. Cut the pipe to the same length as you measure from
just in front of the front tire of the MC to just to the rear of the rear MC
tire. The pipe guarantees that you get good tire point contacts on the front
section and the rear section of the sidecar tire. Otherwise, take a 4" x
2" straight board, wide side flat, sitting on a front and a rear brick,
again to get the reference points off the ground. Just at the rear of the rear
MC wheel, measure from the line to the outside of the pipe, call this width
"A". Just at the front of the front MC wheel, measure from the line
to the outside of the pipe, call this width "B". Then toein is the
difference, or the value "A" - "B".
4.
This is your starting point. Test drive, Change until you get the very best
handling. Do not make big changes.
5.
All items work in harmony. Leanout, 1 to 2 degrees, or 1/2 to 1 inch, measured
from the saddle. Use the line running up the centre of the rear tire to
determine angle of bike.
6.
Leanout wants to make the bike want to turn to the left. Picture a solo bike
leaned over to the left, it wants to go left.
7.
The drag of the sidecar wheel from its weight and the friction of the SC wheel
axle and the drag of the SC tire, wheel, etc tends to want to make the rig go
to the right.
8.
The frontal area of the sidecar, build as a box with a drag of a stone, tends
to make the rig go to the right, more so at higher speed.
9.
The crown of the county road tends to make the rig want to turn to the right.
10.
The toein of the sidecar wheel tends to make the rig turn to the left. Too much
toein and you will get excessive tire wear, especially on the rear. I have
shredded the rear tire from new in 700 miles with a near empty chair. You cause
the tires to scrub against each other. If you see the tread is feathered you
have a badly setup rig which will eat tires.
It
is your task to balance all these right and left turning forces so that your
rig goes straight ahead. A poorly setup rig will wrench your shoulder out of
place in a few hundred miles. A well setup rig will be a pleasure to drive.
This task is more easily resolved by fitting either an adjustable lean control,
and/or an adjustable toe-in control
Bottom
line - no magic numbers, just a place to start. If you have a BMW, begin with
their recommendation, Same for H-D.
Remember,
the smaller the trail, the more twitchy the steering. Racing outfits go down to
near zero. Street hacks from 1.5 to 3.5 inches. For high speed solo tourers
from 3.5 to 5.5 - no magic numbers. The larger the trail the larger the
self-centering force. The smaller the trail the lower the self-centering force.
Self-centering force is seen when the rig wants to straighten itself after you
turn into a corner. It also helps to dampen the dreaded wobbles.
Lead is mainly to minimize
the bike from flipping over on sharp left-handers. Keep weight in SC to rear.
Too much lead causes more scrubbing force on lefthanders. Also on righthanders
except that sidecar wheel is light because of centrifugal force. No lead makes
for easier steering. Again, no magic numbers. Most seem to operate from 8 to 12
inches, some have gone to 15 inches.