911911

I’ve just replaced my second set of Pirelli pzero rear tyres. The first set of tyres were set at the recommended 44psi and after 10k the middle section had worn significantly more than the sides. The second set were set much lower at 38psi but similarly the middle bit had worn out well before the sides.

Does this suggest that they’re still over-inflated and, does it also mean that the whole of the tyre isn’t always gripping the road?

Would anyone know what difference it would make to the handling if the rear tyre pressures were to be set at 34psi (and lower the fronts to 30 or 32)?

Thanks

1999Porsche911

Because of the negative camber setting on the rear wheels, the inside of your tires will become bare in as little as 8000 miles. If you are not tracking the car or driving to the extreme on corners, get an allignment and have them dial out some of camber. Always run 44 psi in back and 36 psi in front.

gota911

I had the exact same thing happen to my first set of P-Zeros running 44 PSI, only mine wore out in the middle of the tire at 8,500 miles. I wrote Pirelli and complained about the uneven tread wear. I got 50% off next set of rears. Like you, I ran the next set at 38 PSI and got 10,500 miles out of them, and the wear pattern was more even across the entire tread.

By the time the second set of rear tires wore out I also needed to replace the front tires, so I went with Bridgestone RE750. They are NOT "N" rated, but after 4,000 miles, they are wearing very well. At the current rate of wear, I "project" 20,000 miles from the rears.

The RE750's ride is harsher than the P-Zeros and that may be due to harder rubber compound and stiffer sidewalls. I notice the harshness mostly when driving over highway expansion joints. FYI.

10 GT3

I am running a ROW M030 suspension with GT3 control arms and an aggressive alignment with -1.6 camber front and -1.9 rear. I run Bridgestone S03s on the street. These tires have a much stiffer sidewall than the Pirellis and hence the ride can get pretty rough. I now run 34 psi in front and 38 psi in rear. I get a very neutral attitude in corners, acceptable ride and no accelerated tire wear. In fact, they wear much more even with lower pressures.

Unless you always drive your car like a grandmother in a Caddy on a Sunday drive, you should not see camber wear with even -1 degree camber in front and -1.5 rear (my old alignment settings). Before I went to the aggressive alignment, I did run the recommended 36/44 and I was getting greatly accelerated wear in the center of the rears, so the pressures were definitely too high. I do wear my rears pretty fast (they won't last 10K a set). The fronts on the other hand hardly wear. They have only worn 2/32" in the last 6000 miles, including a couple of track days.

911911

Thanks 1999porsche911 but it's the middle of the tyre that's wearing faster than both sides. I accept what you say about the camber if only the insides were wearing out quicker than the outsides ....... or maybe I hadn't notice the inside tread too closely and that they had in fact worn out as you suggest. I suppose 10k from a set of of tyres on a Porker isn't that bad as I only managed 13k from a Merc E class I once had.

1999Porsche911

There are only a few possible causes of the center of your rear tires wearing out faster than the inside half. Among them are, improper allignment and/or grossly incorrect tire pressure. If the camber is correct, you CANNOT wear out the center of the tire without the rest of the inside half. (street driving). The center can only wear out if your camber is close to neutral. So, for those who are wearing out the centers of their rear tires and NOT the inside half, you have incorrect camber setting and/or grossly incorrect pressure in the tires.

911911

The pressures were definitely set at 38psi and I'll get the alignment done when its next due for service in October.

Any idea what difference it'll make to the vehicle's handling if these rear tyres were inflated to 34psi instead of 44?

The usage is street driving only but on a ceratin stretch of the motorway the car frequently reaches 100mph and at times touches 140 (when it's perfectly safe and on a straight).

fasteddie99

Lowering the pressures in the rear will increase oversteer.

1999Porsche911

Your backend will be all over the place and the first time you hit a pothole with the back wheels, you'll be looking for rims. You'll be amazed at the improvement in handling bringing them up to 44 psi.

When you get an allignment, get them to print out the current specs.

evansaero

I know, I know... Don't trust everything you read but,

I read an article in Total 911 ‘July 2006 Issue 14’ pg 61-67

Kevin Hackett learns to drive on-track and shares his new-found wisdom. My point is that he talks about his instructor pulling in the pits and checking the pressure on the tires. They started the day at the 36/44psi and when checked the first time they were 7psi higher. The instructor lowered it back down to 36/44psi. Later in the day they checked it again and found it to be 7psi higher. He lowered it back down to 36/44psi. That’s a total of 14psi higher per tire.

The instructor talked about never wanting to be above 36/44psi even when the tire is hot. (He was talking about tracking the car)

On a side note… Is it not true that NASCAR cars fill its tires with nitrogen which is not affected by heat expansion?


Don't kill the messenger. I'm just repeating what I read