Roll Center

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What is the easiest and most practical way to find the Front and Rear roll center on a car that is built with the engine in it? The car would be sitting static on a level garage floor.

I cant follow imaginary lines very well. BLOL

[NickHolt]

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Roll Centers. I could write a book about roll centers...

 

Unfortunately, there is no simple, practical way to accurately pinpoint the front roll center on your race car. You may not like imaginary lines, but unless you actually graph out the front end or put the front-end measurements into one of the suspension geometry programs, you're just guessing.

 

However, here are some quick and easy guidelines to help you get a very rough estimate.

 

Front Roll Center

1) The steeper the angle of the upper right front a-arm, the higher the front roll center.

2) The flatter the angle of the upper a-arm, the lower the roll center.

3) The more the lower a-arm is tilting downhill towards the engine, the lower the roll center.

4) The more the lower a-arm is tilting downhill towards the lower ball joint, the higher the roll center.

 

Suppose your bottom a-arm were parallel to the ground and the upper a-arm were at a 10 degree angle. The front roll center would be about 3 inches off the ground. Suppose both the upper and lower a-arms were both parallel to the ground. The front roll center would be at ground height.

 

Rear Roll Center

Wherever whatever holds the rear of the chassis from slipping off the rear axle in a turn (might be the panhard bar or the rear leaf springs) connects to the chassis is basically the roll center of the rear. With most leaf spring set-ups the rear roll center is about at the top of the axle tube. With a panhard bar, just measure from the ground to wherever the panhard bar crosses the centerline of the car.

 

You always should have the front roll center lower than the rear roll center.

 

Nick Holt