Hey guys a couple of friends are telling me when I go bak to the track to lower my rear wheel tire presure. What would this do for me and how much should I lower it? Thanks

 

On street tires? Not to much if so you will concave the tire contact patch and and the effect you would have less traction than you had before. It's really hard to do in a street tire due to the lack of sidewalls.

 

My best guess is to go to 22 pounds in the backs and have 35-40 in the fronts.

If you have too little air the rear tire will "cup" on launch. That is when the tire squats on the pavement under the relatively stiff sidewalls and the center of the tire lifts off the ground thereby reducing the size of your contact patch. The result is wheelspin.

Too much air, and the little flex you gain from sidewall flex is non-existant and you spin.

The goal is to have enough tire pressure not to cup, but less than in regular street driving so you gain some sidewall flex to soften the shock of a hard launch.

It is a trial and error process with each car to determine the proper amount of tire pressure. In any case, put plenty of air in the fronts to minimize rolling resistance and to provide a longer rollout in the staging beams.

 

And with a true slick tire, you increase the air pressure until the tire breaks traction. Very low pressure isn't wanted because it increases rolling resistance and too much air causes the tire to run on a narrow contact patch reducing traction. You want to lower the pressure just below the point where the tires have too much air and won't hook up. Heavy cars, 3000+ pounds, need more air pressure than light cars.

A street radial tire however isn't designed for low pressure. As mentioned above, low pressure causes the center of the tire to cup up because the stiff sidewalls won't roll over. Usually a street tire is around 32 psi. Many times traction can be improved by increasing the pressure to 35 psi. I wouldn't recommend going any lower than 28.