Tire inflation and tread-wear-line

spearfish25

Alright tire gurus...I have a question for you.

At the track this weekend, a guy came up to me, looked at my tires and suggested I change my inflation pressure based on where the visible road-tire contact point was on the tire surface (the wear-line). He pointed out that the tires have an arrow that indicates where the belt meets the tread surface, and said that the ideal tire pressure would result in the tread-wear-line aligning with this point. (Think of driving on a dusty road and then looking at the tire tread to see where the dusty part stops in relation to the edge of the tire). He said that if the tires are underinflated, the tire will 'roll over' and the wear-line will extend past the arrows (too far laterally). Conversely, overinflation would bulge the central portion of the tread and the outer tread would not be in contact with the road (moving the wear-line medially).

So, at the track I was running cold inflation pressures of 35psi resulting in a warm tire pressure of 40psi. With the hard cornering, this put the wear-line right at the arrow indicators. Back on the regular streets, the wear-line has moved inward from the arrows implying the tires are overinflated.

Is there any truth in what I was told. Should I be dropping my rear tire inflation pressures on the road to get this wear-line back out to the edge of the tire at the arrows? It seems the front tires being narrower and having the additional engine weight get the wear-line out to the arrows at 35psi cold. I've since dropped the rears to 32psi and I'll see where that puts the wear-line.

Any thoughts or advice would be appreciated.

ChrisSlicks

There is some truth to it, but it isn't necessarily the way to the fastest times, just longer tire life. The Z is front camber challenged so you're going to get tire roll over, you just need to minimize it to make the tires last. Using the marker is a good reference, you should chalk your tires to see how much chalk gets scrubbed off. I used to run pressures as high as 45 front hot in my G35, but I'm down to around 40 now in the Z.

I wouldn't reduce my street pressures to try and meet the line, you're tires wont last as long.

spearfish25

So you continue to run the factory recommended pressure of 35psi cold for both front and rear on the street?

ChrisSlicks

Yes. The street pressure is a compromise, and 35 is a pretty reasonable number. The street isn't a race track so you're not rolling the tires as much. There is less tread depth on the outer edge so you don't want to be rolling the tire to the limit all the time.

spearfish25

Good point about the tread depths. Also, the front tires don't seem to vary as much between road and track wear-line as much as the rears do.