Tire heat cycles

[clarkie49]

as more and more people start with the track day craze they are asking about heat cycles on their tires. i have copied a few different paragraphs from different car/bike racing tech pages for people to look over and try and understand what is going on.

these are not my opinions, just what i found

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Another good idea is to track is the number heat cycles your tires experience. Each time your tires get hot they release chemicals from deep within the rubber. As the chemicals are released the tires lose some of their grip. You can see tires that are hardly worn lose their grip due to heat cycles. Count the number of heat cycles that your tires go through and you may find a repeatable pattern that lets you know when to get that new set
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Q:_ What is a heat cycle on racing tires? How does it affect the wear and grip of a tire?
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A:_ A tire heat cycle is when a tire is brought up to operating temperature and run for some laps, then allowed to cool. Taking a tire through a heat cycle changes its chemistry. In most instances it stabilizes the tire compound by decreasing its heat generation. But that process also slightly increases the durometer hardness of the tire. So scrubbing the tires (one heat cycle run) will help the tires run a little cooler and wear slightly better.
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Successive heat cycles will continue this curing process. Eventually the tires will not provide nearly enough grip because they have gotten too hard, but they will wear like iron. Each heat cycle cures the tire rubber more and makes in harder.
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Keep good records on each of your tires so you know how much use – and how many heat cycles – each of your tires has.
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Heat Cycles: Heating your tires for practice and then keeping the warmers on between practice sessions saves Heat Cycles (the # of times a tire gets hot and then cools) which age your tires (the tire goes "off" meaning the best grip is gone).
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here is my 2c..... if the correct operating temp for your tire is 180' F (just a number i pulled out of my ass), and with a brand new tire it takes 2 laps to warm you tires up to operating temperature, then the next day ( i am spacing it out longer than a session) it may take 3 laps, then 4 laps etc.

at a certain temperature a tire's compounds have a chemical reaction which makes the tire sticky and gives it more grip, after each heat cycle the tire hardens and then it takes longer to get to that temperature.

each heat cycle hardens the tire (as explained before), if you cool the tire very slowly it is less likely to harden as much as if you pulled off the track, parked the bike on a stand and let the ambient temp cool the tires. this is why a lot of trackday riders/racers will put their tire warmers on but not plug them in, the insulated blanket will slow down the cooling effect.

chickenhawk tire warmers also have a low temp setting where you can almost have the warmers on the low setting all day.

of course if you live in Ariziona the 110'F air temp and 130'F track temp means you dont really need warmers

[hakan_olsson]

Good reading Clarkie!

As a typical medium slow track day rider. (about able to get the knee down, here and there , what would be considered - to many cycles on a let say RS2/SC2 or even pirelli/metz road compound? 4 or 20 cycles? How bad does it get?

The other thing, when the the rubber gets harder, (due to the heat cycles) can you get back same or similar grip, but one just need warming them more/longer and to a higher temp? I guess, I could ask the same by saying - as long as you get them to the correct stickieness/softness - you are OK? Or perhaps, that's a poor yardstick to use?

My rear Supercorsa roadversion (the ones when I bought the bike - new) look really worn out. Not flat but just a mm left. They are past three track days plus 2500 miles road. Still, I'm unsure whether they could perform quite OK on another track day.

/h

[clarkie49]

i good indication of the tires having too many heat cycles on them is that they look fine as far as the tires not being overly worn, but the are a blue/purple color on the edge of the tire.

this doesnt mean that you cant use them any more but more you just have to be ready for them to have a little less grip than they used to.

Pirelli tires - i use the pirellie itres back in2002 on my GSXR750 doing AMA Superstock racing and they are a freak'n awesome tire, the only reason i chose to race on Dunlops was that i won a championship for Dunlop and they wanted to give me free tires to race with, and pirelli did not. in the end i think the Dunlops are a better tire but that is another story.

ok, back to my Pirelli rant

the SC1 (blue) front pirelli is such an awesome tire we were getting at least 15 practice sessions/qualifying/races fromt the fronts before we would change them, and then we would only change the fronts because we thought we should. the pirelli tire construction is different to the dunlops, which is different to the michelin, so it is hard to compare them directly.

the one thig we learnt using the pirelli tires is that you cannot chucnk a pirelli tire, the contruction doesnt allow that to happen. i had a bet with the Eact Coast Pirelli distributor (Moose) at Road America when i was doing the demo/trackday thing for Aprilia that i could chunk the rear tire Road America is a hard track on tires, especially a stock RSV with headlights, kick stand and stock sacs shock, well i came in after spending all day on the same rear (that had 2000 miles of street track riding on it before i started) and there were quite a few cords showing, but the tire looked like new (where there was still rubber left )

the AMA superbike privateers that ran daytona use 1 (blue) SC2 to run the whole 200 miles, my bro-in-law (Scott Jensen) who has raced on Pirelli for 3 years now said that the biggest difference with the SC2 (green) front over the SC1 (blue) front is that the SC2 takes half a lap longer to 'come in' and he also described it like the SC1 with 3-4 heat cycles on it.

another thing to note with the Pirelli tires is that you want a hot pressure of 34-35psi front and rear. if you start with 32psi in the rear and you check it straight after you get off the track (before you get time to take your gear off) and it is reading 37psi, its as easy as taking 2 psi out of the tire so now you will be at 30psi cold. remember every rider and track heat a tire differently.

for example, at Daytona the pirelli riders set their tires at around 24-25psi cold, they say the bike feels 'squishy' on the first lap but the tires will last 18 laps around daytona without any problems

you sort of right by saying that a tire with more heat cycles takes longer to get up to temp, but it is actually more that a tire with more heat cycles needs a higher temp to release the checmicals in the tire that make it sticky.


i would spring for another set of tires, price up a set of tires vs a lowside crash and you will be way ahead, not to mention you will be more confident and have more fun with new tires that grip




*** i have some supersecret info on the Dunlop slicks as well but i dont think anyone is running them, if you are running dunlop slicks PM me and i will give up the info that Jim Allen doesnt want you to know

[hakan_olsson]

Yes, I've had strong blue/purple color after each track day. Perhaps the bike is now worth a new set of fresh tyres

The hot pressure, I like. Why even bother adjusting pressure when tyres are cold? If I understand this right, the final goal is to reach a certain pressure - during the actual run. That for any make/model. As you say, various conditions will heat them differently. I can't really get why manufacturers list pressures in "cold". Kind of useless info, or at least quite inaccurate.

Thanks again for great post

/h

[clarkie49]

i think they publish them 'cold' becuase how do you define hot? the heat that a professional racer can get into a tire is more than a trackday rider.

same with tire warmers, they are all set to different thermostats and so again heat the tire to a different temp. a good idea is to measure the tires hot straight off the track, and then check them when the tires are cold (ie, cold to the touch) and then you have a starting temperature.

you can go one step further and check them with your tire warmers on and wait until they have cycled at least two times and check the pressure.

another way to make sure ( and this is for the racers out there ) is to get a temp gun so you can stay consistant.

for our dunlops we want to get a 2-3 PSI rising rate from when the tires are set hot with our Chickehawk tirewarmers after they have cycled at least two times.

if you are not using warmers, remember that as the day heats up the ambient temp changes and so if you start with 30psi cold at 9am, it may actually be up to 34psi cold around 2pm. so in other words check every couple of hours to make sure that 30psi cold is still 30 psi.

as for our 'Super-secret Dunlop Pressures' i cant tell you, all i can say is when i was first told what to run i called bullshit. the answer i got was "well it worked for Matt Mladin at Fontana" and you know what, it worked for us as well

[stinky]

So how many times can you make 'em blue and still use them aggresively?

I've got a set of diablo corsas that are blue right now from the last ride - they get that way every time I go to the twisties. Still have lots of tread on them after 1600 miles, and they're about to make a twisty trip to Laguna Seca and back to LA.

[clarkie49]

you can still use them, just be a little more careful and make sure there is plent of heat in the tires before you throw it into that turn

riding in a straight line will not bring the tire up to temp properly, our tires some in off the track so hot you feel like you burnt your hand when you put it on the tire but the grip was perfect and the tire is wearing perfect as well.

obviously they wont get that hot on the street, but just cruise through the first couple of corners and throw it in after the first couple

[hakan_olsson]

Originally posted by clarkie49
i think they publish them 'cold' becuase how do you define hot? the heat that a professional racer can get into a tire is more than a trackday rider.

Oh, ok. But in general, a tyre should have a fixed amount of air pressure - to support its mechanical structure, design etc.(?) If two riders "Mr Superslow" and "Mr Superfast" use the same tyre, bike, body weight etc etc on same track. After 30min, Mr Superfast's tyre is going to be very hot. Mr Superslow's tyre will not be near as warm. A technician from the tyre manufacturer is waiting in the pit to make an emediate pressure adjustment asap when they arrive. The tech guy finds higher pressure than optimal on all 4 tyres. He would let out air until pressure is according to his prefs, but most important - to same final pressure on both bikes. Right?

I might have all this backwards but if it's about right - the manufacturer could very well publish a kind of a "Actual tyre pressure" The pressure everyone should have, while and well established in the environment. Well, you can't measure while riding but probably as you wrote, after stop comming into the pit would be a lot closer to "real" than trying to hit the target by filling them up when cold?

/h

[clarkie49]

no you are correct - does that even make sense?

you have two riders, 'super fast john', and 'average joe' go out on the recommended 31psi pressure and 'averages joe's' tires come in with the correct hot pressure (lets say 34 psi for example using Pirelli's reccommended hot pressure) you can bet that because that 'superfast John' will be working the tire harder, spinning it more and his tire might come in reading 37psi.

this would mean that to reach the target pressure of 34 psi which is the pressure and also temp that the tire works the best, 'superfast john' will need to take 3psi out of his tires and be starting at 28psi cold.

here is an example for you, i measured my rear tire cold once and it were 24psi, cant tell you what compound or track it was at but the hot temp was 32psi and the grip was awesome and the tire didnt tear up or even wear very much.

i friend of mine races on michelins and for a while he was getting Colin Edwards RC51 WSBK takeoffs from Laguna seca that has 4-5 laps on them. he is an AMA superbike level racer who has finished top 15 and he could never get enough heat in the WSBK A-spec tires to make them work properly. the RC51 had probably 30hp over his bike and CE is a lot better rider (obviously) and the combination of rider and bike worked the tire carcus more than he could.

[scott2ride]

And don't forget gentlemen..... Road tires are different than Race tires. Road tires are designed to have multiple heat cycles and still be ok.

[clarkie49]

yes, but we are talking about trackday tires, in particular the SC1/SC2 tires that a lot of track riders use. trackdays are huge over here and only getting more popular.

but, if you D208 street tires are blue from carving the canyons you should still be a little cautious.

we all know the tire of choice is the MEZ1, so you should be ok scott

[scott2ride]

Yep I realised you were talking Race rubber, but thought I'd mention it in case someone just scanned the thread and got the wrong idea.

And MEZ1... No no no no no


Mitchellin Pilot Powers thank you!

[Johnny in Oz]

Originally posted by clarkie49
no you are correct - does that even make sense?

you have two riders, 'super fast john', and 'average joe' go out on the recommended 31psi pressure and 'averages joe's' tires come in with the correct hot pressure (lets say 34 psi for example using Pirelli's reccommended hot pressure) you can bet that because that 'superfast John' will be working the tire harder, spinning it more and his tire might come in reading 37psi.

this would mean that to reach the target pressure of 34 psi which is the pressure and also temp that the tire works the best, 'superfast john' will need to take 3psi out of his tires and be starting at 28psi cold.

This is indeed a timely thread. Tyre pressure is the single most important trackday issue for me. If I at least "think" I've got it right, then everything else seems to fall into place.

I've never considered the 'heat cycle' issue , so this is more grist for the mill.

I'm not sure I agree with the your example though, since the lowering of tyre pressure for 'superfast John' would cause the tyre to actually heat up even more thru the increased friction of the the carcass moving around more. So if you want to reach the target pressure you need to actually put some more air in the tyre. I know this seems counter-intuitive, but that's the physics of it I think.

I'm also not sure I agree with a "target pressure", as such, since there a far too many variables in the picture like ambient/track temp, weight of bike/rider, type of machine, even the time of day etc. I apologise in advance if I've misunderstood your point, but I always understood the issue to be getting the tyre to its operating temperature range (higher for track/race based tyres which dissipate heat at a greater rate and hence their inappropriateness for road use).

The rule of thumb I discovered and have applied for some time is the 10% rule - that is, I aim to have the tyre pressure increase by 10% from cold over the session (15-20 minutes), which would equate to the tyre reaching its operating temperature. I've only ever run road tyres on the track, so tyres like Pirelli SCs would require a (slightly) greater increase in pressure from cold, say as much as 14% (?) The ability to achieve this 10% increase means that the cold temp would vary across the matrix of variables (weight,temp,style of riding etc).

I drew up a ready reckoner years ago so that I could quickly work out where I was at in trying to get to the 10% increase. I also used to keep records of my tyre pressures and the cold tyre pressure changed noticeably from season to season as well as thru the day as the ambient and track temperature increased, requiring more tyre pressure so as to keep within the 10% margin.

Don't get me wrong, I'm not suggesting that this is the only way of doing it. Just that it's a simple way (for the simpleminded like me) to get the tyre working within it's optimum temperature range.

FWIW.

John

[mike71]

Originally posted by Johnny in Oz

I'm not sure I agree with the your example though, since the lowering of tyre pressure for 'superfast John' would cause the tyre to actually heat up even more thru the increased friction of the the carcass moving around more. So if you want to reach the target pressure you need to actually put some more air in the tyre. I know this seems counter-intuitive, but that's the physics of it I think.

[hakan_olsson]

Not worth a dime but, I would say

If the pressure is to high. You let some air out. Not in

Similar, If the pressure is to low, you have to pump it up.

Sure, the temp will work or act in the opposite direction, due to friction changes etc. But, att the end - you just don't need to increase/decrease pressure as much as what the numbers initially tell you to do. Or, the pressure increase you get from lowering-the-pressure-to-get-more-heat isn't big enough to even bring it back to the starting point. The net will be a lower pressure.

I could be wrong though

/h