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YOUR RESEARCHI feel lame asking but what tire pressure are you guys running?
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Replace 4 bridgestones
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I replaced all 4 Bridgestones with PS2's and they have been great.
I feel lame asking but what tire pressure are you guys running?
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I feel lame asking but what tire pressure are you guys running?
Run 295's rear and 235's front
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I feel lame asking but what tire pressure are you guys running?
Run 32 all around
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I feel lame asking but what tire pressure are you guys running?
Run 32 front and 39 rear and get even wear
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I run 32 front and 39 rear and get even wear on my tires.
I feel lame asking but what tire pressure are you guys running?
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30 front 32 rear - I'm very interested in this as well.
These pressures came to me from an experienced DE instructor who has been tracking his '99 since he bought it new in '98.
I gotta admit the pressures worked great for me at the track, and on the street it's just fine - nice ride (eliminated the hard thumping) and puh-lenty good turn in.
Manual for my 02 C4s says 36 44.
Low pressures could be dangerous because of over heating.
Most likely you will never hear of a blow out from over pressure;
however, quite easily if a tire is under pressured.
Just imagine all 8 side walls flexing and bending deeper every time it
goes by the road; the deeper the flex the higher the heat, and it also
causes weakening and shorter life of the side walls.
John
Thanks - I was about to go out and lower the pressure, but I think I'll hold off. It's just the thumping at every bump that's annoying. Does anyone change their tire pressure for cold weather vs warm?
Track pressures and street pressures aren't and shouldn't be the same. Track pressures, AFAIK, allow for the likelihood that heat will cause them to increase when you're out there. In the recent Excellence piece where they tested the GT3 RSR versus the RS, for example, the tire pressures in the street car went up by 10 psi when they were lapping it! (the RSR was running nitrogen to prevent this).
38 - 40 rears pumped. front slightly lighter.
check my pressure every couple days in Minnecolda. 8 degrees this morning and going down...same as my tire pressure! -20 possible this weekend. Coldest of the last few years. Car will stay in the heated garage, so will daddy.
Yes - this is all true, and I should probably run them higher on the street...but tire wall flexxing? I don't think there's all that much flexxing of my 295/30 tires on the back of my car. Seriously - a blowout is not really a consideration here.
And short life of the sidewall? I got barely 10,000 kilometeres out of my Pirelli Rosso tires last time around. C'mon!
I run 36F/44R COLD for street tires on the street. Those are the factory recommendations. Thumping on bad expansion road joints are noticeable, but that's because it's a Porsche suspension, aggravated by the fact that you have a C4S, which has the sport suspension standard.
I run 36F/44R HOT for street tires on the track. Track use generally will generate a lot more heat in the tires compared to street driving, and can easily raise those pressures beyond the max pressures.
Track tires or R-compounds on the track are a different story.
As others have stated, the manual states 36 front and 44 rear, which is too high, IMO. I run 32 front and 39 rear and get even wear on my tires. When I initially got the car, it had P-Zeros on it and at 44 in the rear, I had an unusual amount of wear in the center of the rear tires.
Thanks to this thread, went to the garage to check on my tire pressures, lucky I did bc all 4 were way low. I set mine to 35F 40R like "Crazy" above and so far no un-usual wear.
I ran N specs Rosso on my C2 with 34F 40R and I had more ware in the middle on the back tires.
Unless you are going high speed over 100mph all the time, 34F 38R should be fine for street driving.
36F/38R cold.
I ran 36F/40R cold on my last set of Pilot Sport N1's and got over 27k mi. on the fronts and about 14k usable miles on rears (actually took rears further than that, but that wasn't very smart), which at 40 cold, still wore out in the center of the tire (-1.4 camber rear).
I run 38F/38R cold autocrossing.
Pretty much neutral at those pressures.
Stock pressures, imho, are designed to
insure
understeer.
Jasper
The information I gave you was based on my father's data collection
from one of his projects. He was an engineer at GM.
The charts showed tires being able to withstand much more weight
with higher inflation. And yes, under normal circumstances,
only lower pressures can cause a blow-out, because of sidewall bending causes- heat,
and material break down.
I used to under inflate also, but after seeing the data, I preferred
not to try and be smarter than Porsche Engineers.
I prefer to reach 280 Km/hr with a firm 36 44- safer and less heat,
than under inflated, causing more unstable heat, and possible side
wall problems.
PS I should have said "shorter tire life, from weakening of the side walls."
(of course under inflation would have to be very low)
Ditto, I trashed my P-zeros in 6K miles because I followed that b.s. recommendation. Now I run 32 all around. I don't drive fast or hard enough to worry about the heat buildup, and as a cab, it's not a track car.
Michael
I try to run at around 38-40 psi hot; 2-3 psi higher in the rear than the front (225/285 P Zeros on 18 inch). To reach this on the track on warm days I need to go down to 32/34. For street driving I sometimes adjust this pressure up to maybe 34/36 but not much higher. If you run 40 psi cold on a street tire on the track, you'll measure > 50psi after the session which is way too high. As it's so much depending on the situation, driving style, outside temperature, tire brand and size ... the cold tire pressure is not the right way to measure. For me I figured out that my warm tires should not exceed 40-42 psi, otherwise the cars handle like crap and the tires wear unevenly.
Confused. Lower inflation pressures accelerate tire wear, they don't slow it down. And why on a 911 of all cars would you choose a setup that promotes oversteer?
Tim talked about an unusual amount of wear in the center of the rear tires, caused by overinflation. You're right that in general underinflation is acceleating tire wear but overinflation is accelerating uneven tire wear, so you end up with plenty of thread on the sides but bald tire centers.
Makes sense, I guess, but you'd have to wickedly overinflate the tires on this car to get heavy center wear at the rear. That kind of wear is more consistent with a tire that's too wide for the rim.
With most cars and modern tires, the tread contour on a right-size tire will stay as it should almost up to the max inflation pressure. Anyhoo, hope it gets solved for him, whatever the issue.
Logically, you would think so. However, first set if Pirelli P-Zeros lasted only 8,300 miles and were worn to the wear bars in the middle of the rear tires but still had 4/32ths of an inch (new = 10/32th) on the inside and outside portions of the tread.
I wrote to Pirelli on their USA web site and complained about the unusual center tread wear and verifiied that I ran 44 PSI per Porsche specs. To make a long story short, they gave me a 50% discount on another set of rear tires. Since the fronts still had adaquate tread remaining, I got two new rear tires. I ran the new tires at 38 - 39 PSI and got 13,000 miles out of them. The center and the inside of the tires worn at about the same rate, as you would expect with 1.5 negative camber.
I'll be damned.
Is this just a Pirelli phenomenon? Or do I need to be looking at my PS2s more carefully? I'm a 36/44 guy. It suits me for the street, so it's what I run on both my summer and winter tires.
Bruce,
I ran my last set of rear PS Ribs at 40psi, and got quite a bit more mileage than Tim did, although I ran them longer than I safely should have.
The tires
still
wore out the most in the center of the tire. 1.4 camber.
Hence, have gone to 38psi on current rears.
Learn something new every day. I would have assumed that the most likely area for premature wear would be on the inside shoulders of the tire, especially if, as I do, you run spacers.
Anyway, I won't compromise performance even a little, so I guess I'll just eat the premature wear... but I'll pay closer attention, there, that's for sure.
As Tim mentioned, the tires wore in the middle, severely. As for the second queston, the 996 in stock form will understeer, so a little bt of tire pressure manipulation helps to even it out a bit.
Michael
That depends very much on how you drive it. Compared to, say, my BMWs, I find this car quite neutral, and whatever understeer is there is built in by design for safety. The key with a 911 is its ability to steer with the throttle. The problem is that even a 996 can break loose on you suddenly if you're not careful. Softer rear tires won't just make the car prone to oversteer, but to sudden or unintended oversteer. Running those back tires firm keeps the transitions more predictable and manageable.
My .02, and I realize probably moot for most street driving, but it IS a 911, after all.
I went through 2 sets of Pirelli P-Zero rear tires. I really liked the fact that they were sticky and gripped very well. However, because my car is a daily driver and I drive about 15K miles per year, I was replacing the rear every 9 to 10 months. I am not a tire or rubber expert by any means but I surmise (uneducated guess) that the rubber compound in the inner part if the P-Zero tread is a softer rubber than the outer inner edges. Again, this is totally a guess on my part. BTW - the P-Zeros I had were the previous version, not the newly released (in the last 4 to 6 months) version.
After the Pirelli's I switched to Bridgestone RE750�s and got decent wear out of them but then they started to "cup" pretty badly. I replaced all 4 Bridgestones with PS2's and they have been great. Probably not quite as much grip as the P-Zeros, but in noise level, ride, overall tread wear, I would rate the PS2's better than the P-Zeros. I currently have 11,200 miles on the PS2's and looking at the remaining tread, I expect to be able to get 6K to 8K additional miles out of them, without compromising any safety factors. Running 32 & 39 PSI, the tread wear is really even, with the outside edges showing a little less wear, as one would expect.
Hmmm...
I run Conti's and run 36/44. Other than a little inside wear on the rear, I have very even tire wear. I get about 50,000 miles to a set of rear tires...
...NOT!!! JK, get about 12,000-15,000 miles on rears and can't tell on fronts as I have 18,000 miles and they still look like new.
I run the PS2 as well.....295 in the back and 235 in the front (at least I think they're 235.
Because of this thread I started running 36/40....but now I think I'll back off a few pounds.
Back when the earlier poster said his dad did research for GM I couldn't help but think he was talking about 75 or 80 series cheapo passenger car tires.
I maintain the risk of tire failure because of the pressures we're talking about here are dead zero, and premature sidewalll wear is a non issue because these tires last so short a time anyway. GM wants to get 100,000 miles out of the tires on their cars. We're lucky (damned lucky) to see 20,000.
