Originally posted by Steevo
I have noticed on Surikarn's Set Up Sheet for various races that he has spacers under both sets of blocks in the rear end, therefore raising the suspension arms a little at the back.
Does anyone else do this and what handling characteristic does it provide (ie. what is the effect of doing this).
Steevo, raising the inner hinge pins raises the roll center and lowers the roll moment like Tony stated earlier. However, he was doing it not to gain traction, but to loosen the rear of the car. The reason is that the 2mm chassis is flexible therefore biasing the traction f/r balance toward the rear. By raising the real roll center he loosens the rear of the car to make it "rotate" more- thus carrying more corner speed. The downside is that if you aren't capable of driving at the level of precision that Surikarn, Teemu, Baker, etc drive, then you will most likely oversteer with that setup and it will make you lose confidence in the car while racing.
If you want to understand more- the reason Surikarn would raise the roll center to make the car rotate better is because he feels the he has found the best combination of spring/shock position/swaybar and doesn't want to change that. You may think, well why not just stand the shock up one more hole to make the car rotate better or spring it up in the rear? Most likely the reason is that he doesn't want to make the car seem more "violent" (for lack of a better term) when it actually does begin to break loose in the rear. By raising the roll center he biases a little traction toward the front, but keeps a "calm" reacting setup if or when it may lose rear traction and begin to break loose. It's a LOT easier to "catch" the car when it oversteers in a smooth manner as opposed to slinging the rear around.
On a side note- I have the beginning of a foam tire setup for the Surikarn car on asphalt (very high traction- almost like carpet)
And one last thing- someone already mentioned this, but they were waaay off on the amount of shims (IMO). On the front oneway you need .3mm shimming the diff toward the shaft, and on the rear you need .2mm. Unfortunately, you will begin to feel a "tight spot" in the drivetrain as a result of the .3mm shim in the front, but there is no other choice right now. FYI- I know what the problem is, but I don't know an easy way to fix it correctly yet. Shiming the diff toward the shaft with a zero lash result is NOT the corect way to fix this problem, it is merely a temporary band-aid.