Sidecar Dynamics

 

Effect of Leaning

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

                 

 

From "Riding with a Sidecar" by USCA

 

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 in Sidecar Talk

 

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.

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