STLBLUES

What is a heat cycle? A lap or series of laps?

Another question. My friend bought a set of nice 305-19 pilots off of Ebay that are in ex condition but the outer edge looks like it has been very hot. Do you think his tires were ran on a track and then replaced? They have 80% tread left and were listed as used tires. Why would they replace them so soon? The guy sells them out of Florida and has a few sets for sale most of the time.
Thanks.

Kinkajou

Every time the tire increses temperature and then cools down is a heat cycle. And it is supposed to decrease tire performance a little bit at a time. But fortunately most of us will wear down those tires before it runs out of heat cycles.

AU N EGL

Heat cycle is when the tire is used hard and the tire temp reaches 180-200* IIRC

Slicks have their most grip with 1-3 heat cycles, then fall off from 4-6 or 7 heat cycles, then from 8 to 15-17 heat cycles the grip is OK. But still much better then street tires.

So tread depth has little to do with the tire life of a slick

Most ppl still run them until they are corded

Bill Hetzel

Yea, like Tom said and the number of heat cycles will also vary depending on the tire composition ( hard vs.soft ).
Each heat cycle will harden the tire rubber, you loose some preformance and it will take more laps to get the tire to "come in".
Treaded tires can see a lot of heat , that's why guys run shaved tires, there is less heat buildup and the preformance is more consistant.

Slicks, 1-3 cycles and they fall off? Yep, that's practice, qualifying and the race. If you're runnin' in the front, one set of tires = one weekend.

We track heat cycles by putting a mark on the inside of the tire for each cycle using a china marker or silver Sharpie.

Sidney004

I think it is more appropriate to say every time the tire reaches operating temperature and then cools down....
We don't really know what the boiling points are of the volatile hydrocarbons and elastomers that tires are manufactured of but is fair to assume that they are designed with compounds that have a rate of evaporation that are at or above the operating temperature of the tire(180-200 DEG F) There is of course going to be some evaporation of the hydrocarbons in the tire at lower temperatures, but in my layman's opinion I doubt that driving in non track conditions constitutes a heat cycle. Here is an article on reducing heat cycles:
http://www.racerpartswholesale.com/pdfs/circtrkwarm.pdf
and here is a good thread on conditioning heat cycled tires:
http://forums.corvetteforum.com/show....php?t=1848418

Bill Hetzel

Again, it depends on the composition of the tread compound of the tire. The weight of the car also has a lot to do with it. Soft compounds like the Yoko's, Kumhos will heat cycle degrade faster that the harder compounds. The tread will go away faster too.
Passinger car tires will still heat cycle when driven on the street but the temps they reach is so low that the degradation is minimal and not noticed by most drivers.
While I really don't like to use an infared gun on tires, I have checked the motorhome and 7000 lb trailer on a hot day and seen temps at 140.

Also, on lighter weight race cars, the heat cycle temps will be different.
On a medium compound slick, a heat cycle can happen at a temp of 150 with the best preformance coming at 175, they get really greasy above that. On a hard compound slick the best grip can be as low as 165. Again, this on very light weight cars.