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Old 27 Apr 2008, 01:16 (Ref:2187759)   #1
adambrouillard
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Join Date: Apr 2008
Posts: 31
adambrouillard should be qualifying in the top 10 on the grid
Longitudinal weight transfer question

Ok, I have a setup problem on my racecar. It's called a spec racer and it has equal size tires all around, 63% of weight (1670 lbs total) in the rear and about 100 horsepower and no significant aero.

I have noticed most drivers run more roll resistance in rear than in the front because at full throttle in all but the slowest corners you can not get power oversteer and they are feeling understeer. This however creates bad corner entry oversteer if you do any kind of real trail braking or anytime you have to lift mid corner. Most seem to brake in a straight line and then turn in under power or are constantly fighting oversteer at corner entry ( or not at the limit). This setup feels very unstable to me and before I give up and sell the car I am wondering if this is really the fastest way to drive a car like this.

My question is basically this. When the load transfers to the rear on corner exit, or in their case the entire corner, (data acquisition shows about .1 g acceleration in most medium corners.) does the load transfer actually add load sensitivity at the rear or take it away.

To put it another way, let's just say the rear of the car weighs about 1000 lbs and under steady state corner can achieve 1 g and has a combined lateral force of 1000 lbs. Now we transfer 100 lbs to the rear. The tires are now seeing 1100 lbs, but are they still having to push only the 1000 lbs or does the load transfer actually make them have to push 1100 lbs. In the first case the load sensitivity would increase and they might could achieve 1.1 g or some such whereas in the latter case they maybe could only achieve .9 g. I'm obviously fudging the numbers, but you should get the point.

I have been having a really hard time figuring this out. Normally this is not a problem because you typically have enough power to get the rear tires to the limit on corner exit on most cars. My instinct is to put a lot of roll resistance in the front to try and properly balance the car, I have tried this and it feels much more stable, but I am wondering if I am compromising total cornering power.

Last edited by adambrouillard; 27 Apr 2008 at 01:23.
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