Technical question about tires that have been run hard. I have ridden motorcylces for several years, have friends that race, and have read a lot and understand that (at least on motorcycles) high performance track tires, even though they may still have substantial tread left, may be completely worthless depending on the number of "heat" cycles they have been through. I think I understand this. The explanation includes the heating of the tire, the release of "plasticizer" and the tire is "soft" once it heats up, traction great. However, if the tire has been through its useful number of cycles, the plasticizer is gone and the tire never makes it back to is intended "stick".

Now, my technical question: Can this happen with the Goodyear Supercars? I have suspicion that my Z was at the least driven aggressively (may have seen some track time, but not indicated). The mods on the car when I bought it were minimal, but included braided brake lines. The maintenance manual had "replacement of brakes" highlighted. The owner a competative SCCA racer. Paint peeled from the hub of the rotor (like caused by extreme heat). A few clues pointing towards nothing for certain, but would help explain things.

The car is in great shape, and the tires still have reasonable tread on them, but the don't stick worth a crap (IMHO). ABS kicks on when braking firmly from 50 mph. Wheel spin is an every day occurance (maybe its really just the 385 hp, but mine seems to be a little too much. I can break the tires in 3rd pretty easily (not just a chirp). I am hesitant to buy new tires because: 1) they're not cheap, and 2) I seem to still have tread left.

Any technical tire guy out there that can either confirm or debunk my "tire hardening" theory? Should I just get the new tires and stop my bitching?

 

You might post this over in the Tires & Weels section - there are some gurus who hang out there. I would guess you've hit the nail on the head, but don't know for sure.

 

Wow...now that is an interesting question....sounds like an important issue...I hope some of those tire-gurus chime in....how would one know the condition of hoops on used z-rated tires? Great question.

 

Good question. :yesnod: I don't break loose unless I'm running really hard. Nothing I would consider unusual, but tire do seem to even get that "glazed" look about them. :cheers:

 

Thanks guys! I have just posted in the tire and wheel section. Let's see what we can find out. The Kuhmos are looking better all the time. I'll post any reasonable responses back in this forum as a reply for everyone's information.

 

All tire rubber compounds deteriorate with time and the rate of deterioration increases exponentially with temperature. If you drive on the street and get the typical 20-25K miles from the F1s over two years the deterioration in dry grip will probably not be noticeable.

If you take the car to the track, and especially if you're a ham fisted driver and slide the car around a lot, the tires are likely to "go off" before the tread is completely worn out.

Duke

 

ZO6 stocker, you are on it!
I totally agree as tire traits are tire traits.

Getting car tire info is like pulling teeth compared to getting bike tire info. Just ask a tire company what the optimum heat range is !!!

I would not be surprised if performance tires have a street life of two years at all. One can use the DOT code to attain the production date and calculate shelf life.

As for heat cycling, there is a black art to rubber manufacturing and they now the typical car driver just gets in and goes. I think everyone on this forum has experienced cold tire syndrome with high horsepower.

My .02 is that on a new ( brand new/ never installed) set of tires, is to use ones experience and heat cycle them a couple times. That is curing the rubber and release and mold compound residues.

If one never heat cycles a bike tire it is toast very fast. If one heat cycles the tire at least has a life.

As for shelf life, we bikers like 'em fresh...under a year old from production. Should car tires be any different?

Some postings on the Yokohama runflats indicate that they loss stick'em two years from manufacturing date.

Firestone I believe users a trademark for a softer compound underneath the first layer of compound so as the tire ages, a sticker rubber wears through.

You may not be shocked if I write....just change em every two years $1500....10,000 miles. It is part of performance. Just like a spin out and flat spotting your tires.

If you rode bikes like me, one thousand miles at $300 a set was expected.

So what do we do? Set the car neutral, no over steer no under steer...just a nice four wheel drift!

 

Stocker,
Good questions, but unfortunately, I don't have a good technical answer.
I will give you my impressions and experiences to add to your decision making process.
I run Goodyear Eagle GS-CS DOT legal tires on my Z06 in the SCCA T1 class. I do have enough experience on these tires to say that yes, they do lose performance after numerous heat cycles (something like 6 cycles) to the order of about 1-2 seconds a lap depending on the track.
I would assume this same type of effect takes place on a harder street tire, but to a much smaller degree.
I wore out my front F1 SCs in 3k street miles and 4 DE days. They didn't seem to lose performance during that period, but obviously, they didn't last long enough to really make a fair assessment either. The rears lasted about 15k street miles and 5 DEs with no noticible loss in performance.
After I wore out my front F1 SCs, I bought 275/40-17 Kumho Ecsta to replace them. I did a DE day at Portland with the Kumho's up front and the stock F1s in the back. My impression was that the Kumhos, while a good inexepensive tire, did not stick as well as the stock F1s. Despite the slightly wider Kumhos, and the fact that the rears had about 10k miles and 4 DEs on them at that point, the car understeered as much as it did before the replacement.
FYI, I wore out the front Kumhos in about 10k street miles and 1 DE. I replaced all four tires at that point with Kumhos for cost reasons alone as I was preparing the car for SCCA T1 and only needed street tires for the occassional trip to Hooters. :D
I have used my street Kumhos to break in new pads several times this year and found that it is extremely easy to get them into ABS, similar to your experience with the F1s.
My personal opinion is that the F1 SC is about the best street tire you can buy for the dry or track. Note what cars it is on (Z06, Ford GT, several Ferrari's).
The Kumho is very close to the F1 SC in dry performance, and better in the wet for about 75% of the cost. So it boils down to what you want and/or need.
I believe that if you get a new set of tires, either F1 SC, Kumho, or something else, you will see an improvement in performance.
:cheers:

 

I used some stock z06 tires as autocross tires ONLY

they did indeed become far less stick far before the read wore out.

not useless but far less sticky.

took about 10 autocross events.

 

I think this discussion has convinced me to go for a new set and possibly count a shelf life for tires of about 2 years. I'll drive my brother's '01 Z with intake and exhaust mods this weekend, so I'll know once and for all if I am just a lead foot or if the tires are shot. Thanks again!

P.S. The tire forum came up with no responses the last time I checked. This is the place to be!


[Modified by z06 stocker, 3:43 AM 11/27/2003]

 

I don't claim to be a guru, but here is my .02

When my F1SC's were new I could rip off consistent sub 1.9 60' times. They stuck in the twisties like crazy. Fast forward a year, 10K miles, 50 passes down the 1/4 mile, one auto cross event, one Road Atlanta event. Tires have AT LEAST 50% wear left. But now I can't get a 60' under 2.0, the car is sliding all over the place at RA, and street traction is noticably worse.

WTF??

I called a tire expert I respected and he said "yep, heat cycles have made them hard". He said I could try getting the tires good and warm (high speed freeway driving for an hour type warm) and then let them cool for 24 hours, that I would see some improvement. Otherwise new tires. I did this, can't say I noticed any improvement.

I nursed the tires along for another 5K miles, finally tore them up at the 'lil Talledega road course. Bought new F1SC's AND a set of BFG Drag Radials for the drags. IMO the constant on/off/partial heat cycles of drag racing is very tough on these tires.

Les :cheers: