View Full Version : Rear roll center

06-27-2010, 06:19 PM
Is this correct

The RC is the theoretical point about which the car rolls. The roll occurs as a result of the CG trying to contine in a straight line as the car is making a turn. With the CG being above the RC's, this creates a moment arm, similar to a ratchet, with the rotating head being the RC and your hand being the CG. With the CG height being the same, if you raise the RC then the arm gets smaller, like using a small ratchet. If you lower the RC then the arm gets longer. With the CGH not changed and the mass not changed, the same force to roll the call is there. The only difference is the length of the arm. The longer the arm the more the roll, the shorter the arm the less the roll.

Now that being said, only a few things affect total weight transfer, CGH, lateral acceleration and track width. Note that this is TOTAL transfer. This transfer happens no matter what spring, bar, shock, RC combination is used. What the springs, bars, shocks, RC do control is where the weight is transfered.

The RC's are kind of like Anti squat turned sideways. Think of the upper a-arms as the third link and the lower a-arm as the trailing arms. Just as an increase in anti squat results in the car having less squat, increasing the height of the RC results in the Rt side having less dip. This happens as a result of the chassis links themselves resisting the roll, or squat. And just as when we add more anti squat to the left, the left rear gets more of the transfer, when we add more anti roll (raise RC) to the rear, the rear resists more and gets more of the transfer, and the front gets less.

Now all things being equal, if we raise the panhard bar, we are reducing the arm length and increasing the resistance by the links, thus transfering more weight to the RR and loosening the car.

My biggest point is that more roll does not equal more weight transfer.

06-29-2010, 06:23 PM
I would say that is 90% correct in dirt track racing.The cars roll to such extreme angles that some weight transfer comes from body roll.If you are going to use those principals to setup your car up you are going to be on an island by your self because the people that do understand it won't talk and the rest don't know.

06-30-2010, 05:31 PM
IF your weight center line is above the rear roll center the INSTANT the chassis rolls to the right it moves the weight center line to the right also. This would increase weight weight transfer. The only way it would not is if the weight center line and the roll center were in the exact same place and did not change relative to each other.
This also includes NOTHING for the fact that the pan hard bar on most dirt late models is set up to pull the rear end to the left with body roll which would move the weight center line of the chassis to the right and the roll center to the left increasing the lever arms ratio and weight transfer to the right no matter what.