[duegatti]

I've got 11,000 miles on my original 20" Goodyears, and I am just about at the wear bars on the right rear. My second ever autocross is on Sunday.

I have very limited data - anecdotes, really - on the current limits of adhesion on the street. Keep in mind there are plenty of autocross-like back roads around here. I get the feeling that the rear is breaking loose more easily now.

Would that be considered normal behavior for these summer performance tires near the end of their tread life? Can I expect less traction at Sunday's autocross?

Many thanks.

 

[EuroKip]

I think you answered your own question when you say the rear is breaking loose more easily now.
Yes. Normal behavior. Still considered safe for street use ( caution the rain ) , new tires will always perform better.
As tires age the compound starts to harden giving up traction. It’s also the contributing factor for road noise in later life. Have a good time out there — Be Safe

 

[DriveInHouston]

I think you answered your own question when you say the rear is breaking loose more easily now.
Yes. Normal behavior. Still considered safe for street use ( caution the rain ) , new tires will always perform better.
As tires age the compound starts to harden giving up traction. It’s also the contributing factor for road noise in later life. Have a good time out there — Be Safe

I experienced this in my 2014 Mustang GT. By 2018, the OEM Pirellis had adequate tread left (23k mi. on them) but I experienced the ABS coming in earlier, even in dry conditions. The tires got harder as they are getting old (the car was always garaged) and lose grip.

I had a similar conversation with the indie Porsche shop owner I went for an oil change, earlier in the year. He confirmed that in his experience, high performance tires age and loose grip faster than 'normal' car tires.

 

[chester7]

I think you answered your own question when you say the rear is breaking loose more easily now.
Yes. Normal behavior. Still considered safe for street use ( caution the rain ) , new tires will always perform better.
As tires age the compound starts to harden giving up traction. It’s also the contributing factor for road noise in later life. Have a good time out there — Be Safe

Agree that rain grip would be worse. But a partially worn tire is better than a brand new tire- less tread wiggle. That is why many new tires are shaved for track purposes.
I do agree that if you perceive more breaking loose your tires are no longer optimal.

 

[duegatti]

Crap. I suppose I could try and drive better.

 

[DriveInHouston]

Crap. I suppose I could try and drive better.

If it makes you feel any better, I got my Michelin PS4S November last year. I estimate half their life to be gone in 7k mi. and all I did was some spirited driving in the Smoly Mountains/Blue Ridge/Skyline Drive. No autocrosses, HPDEs, nothing...

 

[Porsche2018]

My 2 cents would be to get new tires. If the worn tires blow and cause you to crash.......not worth the risk.

 

[duegatti]

Wait . . . .I'm not disappointed in the mileage. I'm perfectly happy with the mileage. I've always planned on getting a new set of tires when I hit the first wear bar, and I expect that is imminent. And if I have issues at this autocross, I'll do it next week.

I meant "drive better" at the autocross.

But what most got my attention in the replies - is a tire that is not quite at a wear bar going to "blow"?

 

[Viffermike]

I'll second (third? fourth?) the call for new tires. A couple of observations from my experience:

• I stagger my tire pressures downward by 3-4 psi as tires age to help counteract lost grip. In other words, on my 718 (just about through my second set of fronts/third set of rears at 22.3k miles): On new tires, I inflate to 33/35. By the time they're worn, they're at 30/32 or so.
• Age is a factor and heat cycles are a factor -- but the bigger one that can actually be felt in real time is tread-row flexion. Once tread rows get to a certain wear point -- i.e., lose height above the core below them -- those rows 'flex' less, and you lose grip because your tires have simply lost the physical ability to move in certain ways. This is the main reason why some (including myself) feel semi-worn tires losing grip seemingly overnight.

I generally replace my tires at 2/32 from the wear bars, if not sooner -- within a month or two of feeling that 'overnight' grip loss. I just had that feeling on my Conti ECSs in the rear, and the rears are only 4.5 months/7.5k miles old. Gonna give a set of PS4Ss a try next, even though I really, really like the Contis (though they didn't wear as well as I'd hoped).

 

[duegatti]

I fully accept and understand that I should get new tires. I'm ready to do that. What I need to know now is involves Porsche2018's comments about a tire blow out.

I don't think I can get tires on before the Sunday autocross. Should I withdraw from the Sunday autocross?

Loss of traction is one thing, and I can accept that. But if there are mechanisms by which a tire like mine is more likely to catastrophically fail (particularly under the stress of an autocross), I need to know that.

There are two more autocrosses this fall. If I have to pass on this one, I'll be disappointed, but wiser.

 

[Porsche2018]

I fully accept and understand that I should get new tires. I'm ready to do that. What I need to know now is involves Porsche2018's comments about a tire blow out.

I don't think I can get tires on before the Sunday autocross. Should I withdraw from the Sunday autocross?

If you are alone on the track I still wouldn't advise participating but if others on the track are at risk, if it were me, I would withdraw.

 

[duegatti]

What would the mechanism of tire failure be under these conditions? e.g., is it simply that the body of the tire is closer to foreign objects because there is less tread, such that a catastrophic puncture can more easily occur? Or some other structural failure that operates when there is less tread? Something else? How is a worn tire more likely to blow?

In case it's not abundantly clear, I am very new to this kind of driving, and these kinds of tires. My flint axe of a 2003 Corvette spent most of its life with me on all seasons.

Just trying to understand and learn.

 

[BlueNorther]

I think your tires are fine for autocross next week. The plan to use them up at the event and then replace them makes a lot of sense. They aren't going to blow up at the wear bars. Just don't drive fast on the highway in the rain getting there and back (hydroplane risk)

 

[duegatti]

Michelins are ordered and should go on Monday.

But I must decide about the Sunday autocross.

I am very aware that rain is a special problem at this point.

 

[DriveInHouston]

Michelins are ordered and should go on Monday.

But I must decide about the Sunday autocross.

I am very aware that rain is a special problem at this point.

I had a Ford Taurus 25 years ago and left for a 200 mi trip with a little bit of room in the wear bars. I had a tire blow out in the return trip. Turns out wheel alignment got progressively worse and at the blow out site I had the proverbial concentric patterns of the worn out plies.

Never again!

 

[duegatti]

Yikes. There's a mechanism.

Porsche2018 - would you care to tackle any of my questions from post #12?

 

[duegatti]

Well, I measure between 3/32 and 4/32 tread in the worst parts (center) of the right rear. Between 1/32 and 2/32 above the wear bars.

My experienced autocrossing buddy from the Corvette club said he wouldn't worry about it. The organizer of the autocross did not have a minimum tread depth requirement, and said I should be fine.

I'm trying to feel good about going. (I worry about enough as it is.)

Would still listen to any Porsche2018 explanation of increased risk in my situation.

 

[duegatti]

I guess it was all much ado about nothing. It took 11,000 miles to get close to the wear bars. 3 miles of autocrossing was not enough to make the tire blow up. I asked several people at the autocross what they thought of my tire situation; no one felt there was an issue. I will drive with confidence to get my new tires tomorrow, and look forward to two more autocrosses before November 3.

 

[DriveInHouston]

Did you observe any increase in wear?

 

[duegatti]

The bars are still not flush with the surrounding tread, but it looks like they have been contacted and chewed on just a bit. Unfortunately I did not explicitly measure the tread depth.