Bryce

No my tires are not over pressured. The sides are also wearing fine. But I noticed that the center channel was lower then the sections outside of the large channels. I thought the center was supposed to be a different compound (like motorcycle tires), so it wears better for high mileage. ???

HPH

I was surprised by how much faster the centers wore -- I was down to the wear bars with lots of tread left on the edges, running 36-37 psi. And, man, did they ever get noisy.

I'm now on my second set of PS-A/S (245/50-17), having looked the alternatives over and decided there just wasn't anything better. I probably got about 20K miles out of the first set. HPH

allroad'Ed now

Porsche had a bulletin out at one time that addressed this. Seems that our wide low profile tires have a tendency to balloon out at high speeds. It is extremely difficult to build a street tire that will be both comfortable for the street and still be stiff enough across the tread to keep it flat at high speeds.

As with anything else, a spinning tire has centrifical force applied to it. Since the sidewall areas are closer to the rim, they remail relatively stable. But the center of the tread is not as well supported and will balloon out at high speeds partially because of centrifical force and partly because the sidewalls are deflecting. the best way to see this in action is to watch a drag racer leave the grid- the tires balloon up and actually raise ther rear of the car from the change in height.

Porsche's recommendation- and one that worked for me- was to actually INCREASE the rear pressure for high speed driving. The rationale is that there isn't much we can do to overcome the laws of physics- centrifical force- but we can address the sidewall deflection. Increasing the air pressure stiffens the sidewall and will result in decreased wear on the center rib of the rear tires.

In fact for many years, Porsche stated in the door jamb of the car a higher air pressure in the rear of the car for high speed driving. My old 930 was 29 f/ 36 r for normal driving, but 29/45 for "extended high speed driving." I followed this advice over 3 911s and never experienced the typical Porsche uneven wear.

Could this be the case on our allroads? Don't know but it makes sense. Porsche 911 rear tires through 1994 were 225/50 on 7" rims. We are running 225/55 on 7.5" rims (or 245/50 as in my case.) Might be worth a try. I for one will always raise my tire pressures by 5 lbs before a long interstate trip. And having run 225/50-16 A/S on my old A6 with 7" rims with 40 psi for my weekly 600 mile round trip commute, I never saw any uneven tire wear. At 12,000 miles, teh tires still had 75% life left when I got rid of the car.

itacud

But, it's not for center tread life - it's to prevent the tire from overheating. The higher pressure does prevent les deflection throughout the carcass, and as less rubber is being bent as it rolls by the ground, it heats up less at higher angular velocities.

In any case - it's good info that you posted. It'd be nice to get a snapshot of the tires at speed, to see what shape they've assumed, with respect to starting cold temps. Ideally, we'd get tire temp recommendations from Michelin, and use a pyrometer to measure hot temps at various speeds and starting pressures. =)

allroad'Ed now

Yes, tire temp is certainly involved. That's something we can test. Next time I'm out playing on a highway, I'll take the tire pyrometer along and try temps at different inflation pressures.

But Porsche's bulletin specifically addressed tire deflection as relates to tire pressure. I'm sure that temp will influence as well.