Tire Pressures

[B-rad]

I recently installed Bridgestone SO2 PP tires in front in a 225/35/17 and SO2 N2 in the rear 285/30/18. Does anyone have a recommended tire pressure for the front and rear for street use.

[David]

This is a pretty subjective area, so please take this as my opinion, and not as any sort of scientific fact. After spending years fooling around with tire pressure on a wide variety of sports cars, I have come to the conclusion that for street use, it is best to stay pretty close to the tire manufacturers recommendations. Perhaps a few psi lower. They will wear longer and more evenly (a significant issue with the NSX) and are safer.

One of the things I often due when I get a new set of tires on the car (I change brands with almost every purchase; I guess I have a short attention span) is to inflate them to spec or very close. Then I track the car and adjust the pressure accordingly. If you know your suspension is already dialed in pretty well, you can make minor tweeks to the handling by adjusting the air pressure SLIGHTY. That is, lower the front or rear tire pressure by a couple of psi based on whether you want to increase oversteer or understeer.

Just my opinion.

[nsxtasy]

David's advice is good, except that there is no such thing as a tire manufacturer's recommendation. All they put on the tire is the maximum pressure, not a recommended pressure.

The automobile manufacturer's recommendation is a good starting point. (Maybe this is what David meant.) That's 33F 40R on the NSX. Then adjust as needed based on handling (oversteer/understeer) as well as tire wear (add pressure if both edges wear before the center, reduce if the center is wearing before the edges).

[David]

Actually, I did mean the tire manufacturer's recommendation, I just wasn't very clear in my choice of words. The max pressure indicated on a tire is sort of a defalt recommendation by the tire company, because they almost universally recommend full inflation. I should have used a better choice of words.

I start there because it is the maximum you can use and I dail down to find the optimum level. I just find that easier. There is no reason not to use the auto manufacturer's recommended level, except that you now move inflation levels in two directions instead of one and the level they recommend is based on the OEM tires, which have different characteristics than other brands. So, for simplicity, I start at the top and work down.

In a related tidbit, some of the research on the Firestone/Expedition tire debacle seems to indicate the damage was largely due to Ford recommending much lower tire pressure than Firestone suggests on the OEM tires. They wanted the ride to be softer.

[nsxtasy]

Actually, I did mean the tire manufacturer's recommendation, I just wasn't very clear in my choice of words. The max pressure indicated on a tire is sort of a defalt recommendation by the tire company, because they almost universally recommend full inflation.

The tire manufacturers call it a maximum because you're not supposed to exceed it, and they do NOT recommend that the tire be inflated to the maximum pressure that the tire is capable of. Doing so will almost certainly give you OVERinflated tires in almost every situation.

[David]

I checked with a couple of tire companies and you are right aobut it being the maximum. However, this still simplifies the proceedure, as the adjustment down in tire pressure is more direct than moving both up and down. If you want to really get into it, a pyrometer will tell you how your tire is wearing accross the tread without having to wait until tread wear shows.