AllWheelDrive

My buddy has an '04 G35 Coupe with stock 17" rims. In long high speed turns, the car begins to oversteer. In sharper corners it seems more balanced. Is this normal handling for this car? I know tires may help, but what about sway bars? Seems kinda dangerous! Any ideas?

vegaseric

First off, have him check the tire pressures. He may need a bit more air in the rears to help keep the rear-end planted. IMHO, the G likes to get a bit tail-happy after its initial understeering behavior.

AllWheelDrive

The tire pressure is at the recommended 30 psi on all four tires. Are people running different pressure?

WashUJon

Wouldn't an increase in tire pressures in the rears increase a propensity to oversteer? I would think less pressure would lessen this propensity.

vegaseric

I guess I should have been more specific. Underinflation of the rears will reduce the amount of traction in most sitations and cause oversteer. Higher PSI in the rear = more traction = less oversteer. You can play around with this a bit if your car is "loose" and raise the rears until you get the handling behavior you desire. Here is a site that gives some corrective measures for understeer/oversteer conditions. Use at your own risk.

http://rogerkrausracing.com/overundr.html

WashUJon

I would assume the reverse is true.

And, btw, recommended cold psi is 35.

AllWheelDrive

Low psi = more tire sway = sliding.
Higher psi will make your sidewalls stiffer, but I'm sure this is good only to a point.

vegaseric

True. If you inflate too high, you start reducing your contact patch and you may introduce some excess heat.

DrRick

actually, the lower the pressure increases the traction. in drag racing, you lower the pressure to get a better launch. in nascar (ok, im a black hick ) you increase the tire pressure in the rear of the car if the car is "pushing" or understeering. it has less to do with contact patch and more to do with the tire pressure acting as a shock. by increasing the pressure, you are actually increasing the rate of the shock. hth.....


Doc

vegaseric

If you lower the pressure your sidewall will deform easier in cornering, effectively reducing the contact patch and decreasing traction. In drag racing you are not concerned with cornering, you are trying to put as much of your power to the ground (in a straight line) as possible. Most drag radials and slicks have a certain amount of flex built into the sidewall to increase traction and are meant to be run at low pressures. You can run street tires on the strip with less air to achieve some of the flex exhibited in drag tires, but they are not as effective. Try taking a nice 90 degree turn after lowering your rears to around 20 psi with your fronts at 35 psi.

I'm going to plead ignorant on the NASCAR reference.

Bottom line, it is a generally accepted practice to increase pressure in the rear (or decrease pressure in the front) to decrease oversteer. Try it out if you get a chance; increase or decrease your pressures in 2 psi increments and note your results.