Tyres and heat cycles, track tyres, how many?
Discussion
Following our other threads about track tyres, when I had a tyre blowout at MAgny Cours last year, there was some speculation as to whether I had put them through too many heat cycles.
The same set of SSRs (remaining tread was fine) had done 6 track days by then and done 1000 road miles too.
Does anyone know how many heat cycles these type of tyres can take - and presumably to the extent that a 60 mile road trip generates some heat, that counts as another heat cycle?
Does it depend on compound, wear rating etc.
Cheers
Ajit
The same set of SSRs (remaining tread was fine) had done 6 track days by then and done 1000 road miles too.
Does anyone know how many heat cycles these type of tyres can take - and presumably to the extent that a 60 mile road trip generates some heat, that counts as another heat cycle?
Does it depend on compound, wear rating etc.
Cheers
Ajit
Ajit, On competition tyres it's usually important to bring them up to temperature initially (before proper use) and then leave them for 48 hours to allow the bonds to reform. Once you've done so they are said to heat up more quickly and remain more stable throughout usage.
Here's some tech talk from BF Goodridge:
"Heat Cycling Makes the Tires Run Cooler
“After a tire has been scrubbed in, its chemistry changes slightly,” Forthofer says. “This usually increases the hardness and decreases the heat generation of that compound. If there is trouble with tires giving up after a long run at a particular track, scrubbing a set of tires will help them run a little cooler and wear better. They also will be a tick slower at the beginning of the run for the same reason. Toward the end of the long run, they will likely be a little faster than the sticker set. Successive heat cycles will continue this trend, and eventually the tire will become too slow to be competitive, but it will wear like iron. The number of good heat cycles in a tire varies greatly with the compounding, so unfortunately I can’t give a number for everyone’s tires.
Lint expounds on heat cycles. “Heat cycles in a tire are good and bad. If you have a tire that is too soft, you can put heat cycles in them to toughen them up a bit and be just right. When you have heat cycles, they are generally curing the rubber and make it harder and harder. That is why when you have so many laps on a tire, the thing starts to drop down in speed because it is ‘curing up.’
“What you need to do is realize when your tires have gone through too many heat cycles. For example, if you have tried to qualify on a set of tires three or four times, maybe that is not the best thing to try and qualify the next race on. You need to get a new set of tires because you had too many heat cycles on the tires.” "
>> Edited by DoctorD on Thursday 26th January 14:25
Here's some tech talk from BF Goodridge:
"Heat Cycling Makes the Tires Run Cooler
“After a tire has been scrubbed in, its chemistry changes slightly,” Forthofer says. “This usually increases the hardness and decreases the heat generation of that compound. If there is trouble with tires giving up after a long run at a particular track, scrubbing a set of tires will help them run a little cooler and wear better. They also will be a tick slower at the beginning of the run for the same reason. Toward the end of the long run, they will likely be a little faster than the sticker set. Successive heat cycles will continue this trend, and eventually the tire will become too slow to be competitive, but it will wear like iron. The number of good heat cycles in a tire varies greatly with the compounding, so unfortunately I can’t give a number for everyone’s tires.
Lint expounds on heat cycles. “Heat cycles in a tire are good and bad. If you have a tire that is too soft, you can put heat cycles in them to toughen them up a bit and be just right. When you have heat cycles, they are generally curing the rubber and make it harder and harder. That is why when you have so many laps on a tire, the thing starts to drop down in speed because it is ‘curing up.’
“What you need to do is realize when your tires have gone through too many heat cycles. For example, if you have tried to qualify on a set of tires three or four times, maybe that is not the best thing to try and qualify the next race on. You need to get a new set of tires because you had too many heat cycles on the tires.” "
>> Edited by DoctorD on Thursday 26th January 14:25
Agent Orange said:
Ajit cud u see where it had blown? Russell ,Zanzibar GT3 , WORE HIS REAR TYRES ON INSIDE REAR EDGES from strong trackday settings and road use WEARING THE EDGES ..............blew at Eau Rouge , think they WERE Corsas...........
Vic, it was Le Source......thank God!
doctorpepper said:
err... whats a heat cycle??
Ok, well you did ask..
"Heat cycling is a very useful thing to know about. But it is not something that many people understand or use properly. A tyre will perform differently when it is new, compared to how it will perform after it has been through a heat cycle. This is not necessarily a bad thing. In fact, in a lot of cases, it is a very good thing indeed. A heat cycle will make the tyre wear much longer, and be more consistent in its performance. By this I mean that the tyre will not change as much during a race or practice session if it has been heat cycled. There will be a slight drop in performance during a session , (lose grip), with non-heat cycled tyres though.
Let's look at what a heat cycle is, and what it does to the tyre. We will concentrate on the tread compound, but there are similar benefits for the other compounds in the tyre that actually hold everything together.
To understand what happens in a heat cycle, let's talk about the molecules that make up the compound. For those of you who don't remember your school chemistry classes, the molecules that make up polymers are long chains of atoms. To visualize this, think of a bunch of rubber bands. Imagine that they have all been cut with a pair of scissors so that they are not closed loops anymore. Now throw a bunch of them into a box and shake it up. Those represent the polymer molecules.
In addition to being highly intermingled, these molecules are connected, (or attracted), to each other by a variety of chemical networks. For simplicity, we will refer to all of these networks as chemical bonds. These bonds, (or attractions), are what we are concerned with here. During the manufacturing process, these bonds form in a more or less disorganized way. Some of the bonds are very short and strong. Some of them are very long and weak. The rest of them vary between the two.
Now, when you take that tyre and run it, things start to happen. The molecules get stretched and compressed. This first causes the weaker bonds that connect these molecules to break. When the bonds break, heat is generated. As the heat builds and the flexing continues, more bonds break, more heat is generated, stronger bonds break, more heat is generated, and so on... Remember that these bonds are what connect the molecules to each other. They give the compound its strength. When this strength is reduced, the compound can't grip the road surface as well. It rubs off instead of holding together. The result is less grip, more slip on the road surface, more heat generated, and more tread wear. You can see that it can become a self perpetuating kind of thing. How fast this all occurs determines how fast the tyres "Go Off".
So then, what happens in a heat cycle that can improve this pretty bleak situation? Well, actually, the situation described above is the first step in the heat cycle process. You want to break all of those "uneven" bonds. Because what happens next is where the real magic of alchemy comes into play. After these bonds have broken, and this heat has been generated, and the tyres are finally allowed to be set aside and relax, the bonds tend to REFORM! But now they reform in a much more uniform manner! This means that they are more consistent in strength. Therefore, the compound becomes more resistant to losing its strength the next time the tyres are run. That doesn't mean that you can't make the tyres give up anymore. If you exceed the limits of the compound, (both mechanical and thermal), the bonds will still break. But they will be more resistant to it because they are working together now as equals (in parallel), instead of individually (in series). And, given the time to relax again, they will reform again in the same uniform manner.
Here is the most important thing to learn, and remember about this process. These bonds MUST be given ENOUGH TIME to do their magical reformation. The tyres must be allowed to relax for an absolute minimum of 24 hrs after that initial "break in", sometimes up to 48 hrs to be sure. But we really haven't seen any additional advantage to waiting any longer than that. If you don't give the tyres enough time to reform those bonds though, then you are going out on tyres with a weakened compound and their performance will show it. Understanding how this works, and how to use it to your advantage, is important to getting the most from your tyres.
Let's talk now about the number of heat cycles you can expect out of a tyre. I've heard people talk about Brand-X, or Brand-Y, or Brand-Z tyres only being good for X number of heat cycles. We really have not seen this with the BF Goodridge Comp T/A R1. You should be able to expect the same performance level from the tyre after 20 heat cycles as you get after 1, (assuming of course that tread wear isn't an issue). Additional heat cycles beyond the first don't make the tyre "harder". The tyre can and will change over time just due to "aging". But that is due to other influences like ultraviolet light, ozone, etc. And that time period, with proper care, should be at least a couple of years.
So, to recap, heat cycling will help improve the consistency and longevity of your tyres. The first heat cycle is the most critical. Subsequent heat cycles do not cause any detriment to the performance of the tyre. It is still possible to overheat heat cycled tyres. But, assuming you don't do any other permanent damage to them, give them the minimum of 24 hrs. to relax afterwards and they should be fine for later use."
So then prof, how is it that a few years ago I`d been racing in Wales, had an absolute blinder, car had just been set up to within an inch of it`s life, I was sitting behind a chap who 2 weeks prior had been running rings round me, I was waiting for him to pull away and he didn`t (couldn`t !). Finished the race put the car to bed, 2 weeks later unwrapped it at Brands and there was no steering or braking. We tried everything. I even put in another driver who I shan`t mention for fear of embarrasing Mark Sumpter of Paragon fame and he put it in the gravel at Druids when the car just ran on.
We scratched our heads and drew a blank, nothing was broken on the car. We fitted another pair of (used) tyres to the front and instantly all was cured. The tyres had just gone off in 2 weeks.
I always imagine long molecules in the tyre that expand as the tyre gets hot then shrink back as it cools. Next time round they can`t quite stretch as far when they heat up, an so on until they stay shrunk and the tyre is dead.
Now of in this instance the tyres were Michelin Pilot Sport Cups which are a competition tyre (of sorts !), rather than a road tyre. The slicks we run behave in the same way and we deem them unfit for race use after 2 - 3 heat cycles & 3 hours of use. There is still pleanty of tread on them - (yes slicks have tread wear markers !). Even for testing they aren`t much good because you end up setting the car up around tyre problems which aren`t there when you fit new rubber.
A "trackday" type competition tyre should be good for more heat cycles than a pure race tyre such as a slick but you will still notice a deterioration in grip over time. Not an issue on a trackday but of concern when racing.
Just my view as a pedler, not a rubber boffin and I`d love to learn the black art !
Henry
We scratched our heads and drew a blank, nothing was broken on the car. We fitted another pair of (used) tyres to the front and instantly all was cured. The tyres had just gone off in 2 weeks.
I always imagine long molecules in the tyre that expand as the tyre gets hot then shrink back as it cools. Next time round they can`t quite stretch as far when they heat up, an so on until they stay shrunk and the tyre is dead.
Now of in this instance the tyres were Michelin Pilot Sport Cups which are a competition tyre (of sorts !), rather than a road tyre. The slicks we run behave in the same way and we deem them unfit for race use after 2 - 3 heat cycles & 3 hours of use. There is still pleanty of tread on them - (yes slicks have tread wear markers !). Even for testing they aren`t much good because you end up setting the car up around tyre problems which aren`t there when you fit new rubber.
A "trackday" type competition tyre should be good for more heat cycles than a pure race tyre such as a slick but you will still notice a deterioration in grip over time. Not an issue on a trackday but of concern when racing.
Just my view as a pedler, not a rubber boffin and I`d love to learn the black art !
Henry
Good points. Fortunately I've always worn Michelin Cup tyres out before I notice much of a performance drop off but it must depend on the rubber compound and the polymers used in the tyre. You would expect an endurance type of tyre to offer greater resilience to degradation than a softer sprint type of tyre. Also much will depend on the chassis set-up, weight distribution and tyre pressures, so I'm not really sure it's possible to generalise about whether a number of heat cycles will affect a tyre or not. It will depend on how extreme those heat cycles were and how carefully the first heat cycling was carried out..
As you know had mine(cups) for 2years road use and about14 track days and no real performance drop off once warm....greasy when cold...and I know about heat cycles from my F3 days where it was an issue...anyway set up for even wear across the tyre more important on a track day than some extreme set up for the ultimate regardless of cost......
Set up for even wear / workload on tyre just as impotant in racing. No point in only using 6 inches of a 12 inch tyre. Tyre temps accross the tyre want to be nice and even. The only reason for the large camber (bottom of wheel sticking out of the the car more than top of wheel), is to compensate for load on tyre as it corners.
There was a chap I raced against that used to have the huge camber angles but drive in a rather sedate manner. The result was tyres bald on the inner inch and brand new on the outer 3/4 !
Henry
There was a chap I raced against that used to have the huge camber angles but drive in a rather sedate manner. The result was tyres bald on the inner inch and brand new on the outer 3/4 !
Henry
I have been checking up on Hoosier tyres as a bloke I know has started getting a few into the UK. On trawling a few of the US sites it is apparent that heat cycling is absolutely critical for the Hoosier brand.
Do it, and fantastic grip and longevity is assured - if you don't, some people have gone through a set in less than a few laps and experienced the sort of issues Henry describes.
The Hoosier suppliers websites gives really good info. Some suppliers will pre-heat-cycle tyres for you for a few bucks so you can just plug and go!
Even their websites don't explain 1 thing that I still can't understand.... What happened to the box and all the ruined elastic bands????
Do it, and fantastic grip and longevity is assured - if you don't, some people have gone through a set in less than a few laps and experienced the sort of issues Henry describes.
The Hoosier suppliers websites gives really good info. Some suppliers will pre-heat-cycle tyres for you for a few bucks so you can just plug and go!
Even their websites don't explain 1 thing that I still can't understand.... What happened to the box and all the ruined elastic bands????
Oh Ok... I understand it now ( no honestly I do! )
So when it comes to the 48 hours in which the molecules are rebonding in a more linear and consistant fashion, does it matter how the tyres are stored? I am guessing to ensure a really uniform rebonding then tyre should be deflated and left to "rest" without any load applied to it? I'd imagine that if the tyres are still on the car when it is resting that the load from the weight of the car would have an effect on the way that the bonds are formed and they would be different at the top (unloaded area) and the bottom (loaded) area of the tyre??
So in short..
1:get some brand new tyres
2:get them up to temperature
3:take them of the car and let them down
4:wait 48 hours
5
ut them back on and happy days!!?
...or is that too easy?
so the next question is How hot do they need to be? I'm guessing this is tyre dependant, so how do i find out what the right temp is for a set of Pilot Cups?
and another question... why dont tyre manufactureres heat up and cool down the tyres before they sell them?
So when it comes to the 48 hours in which the molecules are rebonding in a more linear and consistant fashion, does it matter how the tyres are stored? I am guessing to ensure a really uniform rebonding then tyre should be deflated and left to "rest" without any load applied to it? I'd imagine that if the tyres are still on the car when it is resting that the load from the weight of the car would have an effect on the way that the bonds are formed and they would be different at the top (unloaded area) and the bottom (loaded) area of the tyre??
So in short..
1:get some brand new tyres
2:get them up to temperature
3:take them of the car and let them down
4:wait 48 hours
5
ut them back on and happy days!!? ...or is that too easy?
so the next question is How hot do they need to be? I'm guessing this is tyre dependant, so how do i find out what the right temp is for a set of Pilot Cups?
and another question... why dont tyre manufactureres heat up and cool down the tyres before they sell them?
Oh Ok... I understand it now ( no honestly I do! )
So when it comes to the 48 hours in which the molecules are rebonding in a more linear and consistant fashion, does it matter how the tyres are stored? I am guessing to ensure a really uniform rebonding then tyre should be deflated and left to "rest" without any load applied to it? I'd imagine that if the tyres are still on the car when it is resting that the load from the weight of the car would have an effect on the way that the bonds are formed and they would be different at the top (unloaded area) and the bottom (loaded) area of the tyre??
So in short..
1:get some brand new tyres
2:get them up to temperature
3:take them of the car and let them down
4:wait 48 hours
5ut them back on and happy days!!?
...or is that too easy?
so the next question is How hot do they need to be? I'm guessing this is tyre dependant, so how do i find out what the right temp is for a set of Pilot Cups?
and another question... why dont tyre manufactureres heat up and cool down the tyres before they sell them?
So when it comes to the 48 hours in which the molecules are rebonding in a more linear and consistant fashion, does it matter how the tyres are stored? I am guessing to ensure a really uniform rebonding then tyre should be deflated and left to "rest" without any load applied to it? I'd imagine that if the tyres are still on the car when it is resting that the load from the weight of the car would have an effect on the way that the bonds are formed and they would be different at the top (unloaded area) and the bottom (loaded) area of the tyre??
So in short..
1:get some brand new tyres
2:get them up to temperature
3:take them of the car and let them down
4:wait 48 hours
5
ut them back on and happy days!!? ...or is that too easy?
so the next question is How hot do they need to be? I'm guessing this is tyre dependant, so how do i find out what the right temp is for a set of Pilot Cups?
and another question... why dont tyre manufactureres heat up and cool down the tyres before they sell them?
I've never gone to the trouble of deflating the tyres after the first heat-cycle, I doubt it would make 'that' much difference. Key thing is to allow the tyres to reduce temp (ambient is fine) from normal operating temp.
How hot? Each tyre manufacturer publishes an optimum range of temps for their tyres, but I can't remember what Michelin state for their Cups (and I'm not going to try and guess). Heating them up gently to a decent/uniform temp and pressure is how I've always done it. Half a dozen or so quick laps usually.
The reason why manufacturers don't heat cycle their tyres is that this would then remove the sealant they apply to new tyres, which keeps them all nice and fresh and protects them from UV light and other factors (depending on how they are stored between production and fitment to a car). I guess they could heat cycle them and then re-seal them, but that would cost $$$$$$
How hot? Each tyre manufacturer publishes an optimum range of temps for their tyres, but I can't remember what Michelin state for their Cups (and I'm not going to try and guess). Heating them up gently to a decent/uniform temp and pressure is how I've always done it. Half a dozen or so quick laps usually.
The reason why manufacturers don't heat cycle their tyres is that this would then remove the sealant they apply to new tyres, which keeps them all nice and fresh and protects them from UV light and other factors (depending on how they are stored between production and fitment to a car). I guess they could heat cycle them and then re-seal them, but that would cost $$$$$$
Slicks question for Henry- or Steve Rance etc or others who've run new slicks-
-Do you simply run on new slicks going easy for a few laps then use them as normal, or do a few bed in laps to get 'em to temp & then take them off & use them another day.
Ive heard of both ways being used.
-Do you simply run on new slicks going easy for a few laps then use them as normal, or do a few bed in laps to get 'em to temp & then take them off & use them another day.
Ive heard of both ways being used.
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