M: To find the roll center,...
M: To find the roll center, the exact pivot points must be found. Finding these pivot points of a metric front suspension is not easy. I made this pointer apparatus from 11'4-inch PVC pipe. It is adjustable in all directions. The ends of the pivots must be located in both horizontal and vertical planes. Then the centerline of those points must be calculated.
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Q: I run my metric Street Stock at two different tracks. One is a high-banked quarter-mile track while the other has little banking. Both are dirt tracks. My car works well on the banked track but wants to skate across the turn on the flat track. I've been running with 11/42 inch to 1 inch of stagger. Would more help? The car is set up with 50 percent crossweight and 53 percent left weight. The springs are 900 left-front; 800 right-front; 250 left-rear; and 200 right-rear. There is no sway bar. I have raised the chassis ride height in order to try to make the car roll over into the turn, but that doesn't seem to help. I would appreciate some advice.Adam Via e-mail
Sleepy: First, let's talk about the track with the high banking. Here the car seems to work for you, and it should. The higher the bank, the less critical the setup becomes, with the exception of superspeedways. Consider this: If you raced in a barrel, the car would react as if it were going in a straight line. You would only need enough springs to keep the chassis from dragging the ground. Zero stagger would be needed. So, the closer you get to the ultimate banked track, the less you worry about chassis setup and the more thought you give to engine and aerodynamics.
Going to the flatter track, you may want to make some changes. If I understand your situation correctly, I think there are several problems in the front end of your car. You have light front springs that are reversed from the norm. This could work on the track with the steep banking.
Your car may be balanced, meaning it isn't loose or tight, but it skates across the track. You are getting by with these light front springs by using a taller ride height. As you raise the metric chassis, you raise the roll center, also. In fact, the roll center rises much faster than the chassis. You are in experimental land with this setup. I wouldn't say a car won't work this high, but be prepared to spend the time to try to make it work.
The thing that makes a car shift weight in a turn is the amount of leverage the center of gravity (CG) has over the roll center. When the chassis is raised, for instance 3 inches, the CG goes up the same 3 inches. However, the roll center might go up about 6 inches or more. Now you have reduced the CG's ability to apply leverage to make the car shift its weight to the right side in a corner. If you left the same springs in the car and lowered the chassis to 6 inches, I think you would find the weight shift so drastic that the suspension would bottom out.
You need at least 3 inches of suspension bump travel on dirt. Keep in mind that if the bump travel is too great, the suspension will contact the chassis, stopping the travel. When a corner of the car goes solid like this, that corner will lose traction.
When the car turns left, the chassis rolls to the right. This compresses the right-front suspension. Then the roll center will move down, providing even more leverage against the CG. This is why body roll is necessary with stock-type suspensions.
The rear springs are OK, but may still be a bit strong. The front . . . well? Get the chassis down to around 6 inches in the front and 11/42-1 inch higher in the rear. Try springs 900 left-front; 1100-1150 right-front; 175 right-rear; and 200 left-rear. On the flat track, use about 2 inches of rear stagger. Use front stagger only if you don't have weight jacks. A smaller left-front adds to crossweight.
Remember I'm here and you are there. Start with these suggestions, and don't be afraid to make some changes.