Re: Tire Changing questions

[Tpcutter@xxxxxxx]

In a message dated 6/23/04 12:05:28 AM Eastern  Standard Time, 
jackbunce@xxxxxxx writes:
<<For the BMW content: When I  put my R1100SA on the centerstand and spin 
the rear wheel under power the  bike feels unbalanced and shakes. Yet, I 
do not feel this imbalance on the  road. Should I have the rear wheel 
pulled and balanced or is it normal for  an R100SA to act that way on 
the centerstand with the rear wheel under  power? [This came up because 
I had the bike on the dyno and the tester  mentioned the rear wheel hop 
to me.  So I tried it at  home.>>

The bounce is at least partly due to the  two universal joints in the 
paralever driveshaft. With the bike on the  centerstand, there is a lot of angularity 
in the driveshaft, almost ten degrees.  The u-joints have to accellerate and 
decellerate twice per revolution. The  closer the shaft is to parralel to the 
transmission output shaft, the less  angularity and less accel/decel effect. 
When on the road with your weight on the  bike, and the weight of the bike on 
the spring, the shaft is pretty close to  straight. If you ever "jump" the bike 
so the rear wheel goes airborne, you'll  feel the same rumble from the rear 
as the swingarm reaches the end of its'  travel.

This is a pretty oversimplified description,  but it should help you to 
visualize the forces at play.

Tom Cutter  

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