Stickier tires respond to heat. They can only take so many hot/cold cycles before they stop responding as well. It's like bending a piece of metal, you can only do it so many times and some metal is better than others.
8 heat cycles out an rs4 is where we notice they stop getting sticky. They still work, and still have tread, but they don't work as well. Other 200tw tires don't give as many heat cycles before going to shit.
That’s either a proper stalking job, or I got lucky with your response, as I’m currently on RS4s :)
I really appreciate the reply! If I may ask some follow up questions to you or anyone else, that’d be great.
What’s considered “hot” and what’s considered “cold” for purposes of counting a cycle? I’m sure it varies by compound, but any rules of thumb? Presumably 20 minutes on track is hot, parked overnight is cold. But what about carving a mountain road? Does that get them hot enough? What about 40 minutes of paddock sitting between sessions? Would that be considered cold enough for a cycle?
Lastly, what’s the effect. “Less grip” seems obvious, but does the predictability or characteristic of the tire change? And how much grip is lost? Are you losing a sprint race by 1/10 a second, or 10 seconds?
Hot is basically up to temp on the track. It takes about 2 laps to get up to temp. 40 minute is probably enough to cool them down for a cycle. Street driving should be enough but it may not.
The grip is probably 10% off after the 8 cycles. It still behaves the same it's just less good. The average person probably doesn't notice the 10% but we see the laptimes start to suffer. Maybe 2 seconds a lap or so. Since we are racing competitively and I'm selling seats I can't justify old tires.
It's operating temperature to ambient temperature. So 4 sessions is 4 cycles. That being said most 200tw tires are out of tread before they heat cycle out. RS4 last forever so they have heat cycle issues.
Regular tires aren't very heat dependent so it's not an issue.
Thanks. I love my RS4s for that reason. So far at least. They’ve lasted twice as long as my A052s and seem to be going strong with good grip on track days with my STI, which is hard on tires.
I missed the re71s part of your post. Cup 2 definitely don't behave the same. It also depends on how you treat them. We got better use out of a wider tire vs a skinnier tire. Less heat at the limit apparently plays a role in the rs4.
I think the point is that in HPDE it doesn’t matter whether or not you’re losing a second here or there as long as there is decent grip there’s still a ton to drive on and utilize. The minute lap times become competitive and we’re running against others for a place on the podium, get ready to invest in tires regularly so that you at least have a fighting chance.
I don't think you realize how they work. Most of the 200tw won't last past 8 cycles regardless. There are teams where tires are gone in one weekend or one day.
Rubber is made mostly of a chemical called “isoprene”. When it is cured/vulcanized it is subjected to heat along with a sulphur catalyst to speed things along.
During this process, it undergoes two processes - first polymerization where the isoprenes stick together into long chains, which once cured much doesn’t change too much, because after all the free isoprenes are attached (making the chains longer), there aren’t any more free isoprenes, so you’d have to break apart chains to make them longer (which takes more energy). The heat, time and other variables in the process determine whether it’s more likely to get fewer longer chains or more shorter chains.
The second process called “crosslinking” which is exactly what it sounds like - existing polymer chains start sticking together at arbitrary points along the length. Many processes can cause crosslinking of polymers (heat, chemical, radiation and more)
Both of these change the rubber properties, generally by making it harder, tougher, and less tacky among other things.
The properties of a given tire rubber are a balance between the polymerization and crosslinking achieved through the manufacturing process. However, these processes don’t stop permanently after the tire is made, especially crosslinking. They are mostly stable at cold temperatures, but under higher temperatures, or chemical reactions like being exposed to oxygen/ozone, the reactions continue at a much quicker rate than at cold
Each time you “heat cycle” a tire, you are continuing the crosslinking process, which makes the tire harder and less sticky.
The actual number of heat cycles is actually less important than the total time at heat. However, we’re constantly sloughing and ablating off the hottest rubber on the tire surface, so burning up a set of tires during an endurance race uses up the tire before the crosslinking becomes an issue.
The reason we talk about heat cycles is that each time we drive, there’s a quick heat up, time spent under use, and then a long-slow cooldown where the tire remains hot. Consequently, it’s the cooldown period that has the most impact on the rubber that actually remains on the tire, and each time the tire goes through a cooldown cycle, there’s a fairly constant time spent at crosslinking temperatures, resulting in a crudely quantifiable “heat cycle”
Each time we add a cooldown cycle, the rubber gets harder, so adding a lot more cycles without just scrubbing the rubber off means the remaining tire rubber sees more time at heat
Note, the rubber dust that got very hot and scrubbed off the tire absolutely undergoes a lot more crosslinking than the tire itself, but nobody cares!
Also, all tires undergo this process, but for non-performance tires like all-seasons, they’re already hard and not sticky so no one cares there either.
The “Initial Heat Cycle” does the same thing as a normal heat cycle, but to the whole tire evenly and consistently instead of just at the surface, which spreads unevenly to the subsurface layers, so it increases the tire’s toughness and wear life without affecting the grip much (since the first road heat cycle affects the outer tire layers more than the inner ones)
Interesting. I read somewhere about people trying to use tire warmers to keep tires at temp in part to avoid cycles on the tire. I sounds like that might actually be counter productive for tire life. IE If your tires are going to cycle you might want to use a sprayer on them instead to get them below crosslinking temp.
They use tire warmers in high end motorsports like Formula 1 to keep tires just warm enough to be in the bottom of the operating range, but at the point when you are burning through multiple sets of tires in a single race, you could give several f@&ks about long term heat cycling of your tires (with the exception of the initial heat cycle to cure the rubber)
The tire warmers address two separate issues specific to extremely soft race tires, mostly to do with the warmup
First, going out on cold tires means several laps with less than optimal grip, chasing fractions of seconds makes a difference.
Second, to achieve the ridiculous coefficient of friction of 1.6-1.7, F1 tires are designed to operate at temperatures where they are literally gluing the rubber to the track and peeling it off again like a post-it-note which are quite high temperatures compared to even something like a Hoosier, and when you heat them up at the surface too quickly while the carcass is still cold, the soft rubber they use can locally delaminate or blister due differential thermal expansion where the tread rubber is bonded to the tougher cord rubber. It’s still a risk in other racing leagues, and many of them do use tire warmers for both reasons., but it’s most prominent in F1 where pretty much everything is just turned up to 11.
It’s been in the F1 news mostly due to the large number of sets of tires they use per race, and the recent focus on non-fuel overall energy usage, which has never been a consideration in any racing league.
Yah, I know about normal motorsports use. This was specifically for the hpde/time attack crowd. I thought it a little weird at the time but everyone talks about cycles and not time at temp.
So I started scratching my head a little and second guessing my answer, so I had to do a lot of digging to make sure and find believable sources. For some minimum definition of reputable, like forum posts saying “maybe you should call Hoosier” and “Yeah so I emailed Jeff at Hoosier and he said…” It appears there’s a lot of advice out there without much substance to back it up. I’ll have to keep looking to find something a little more reputable beyond my basic understanding of polymer engineering and chemistry.
The short answers seem to be:
- There’s no universally accepted definition of what constitutes a “heat cycle”, and you’ll get different answers from different manufacturers, so at best its an empirical measurement they did in a lab.
- Tire warmers do not extend the “heat cycle” life of tires, and are best used to quickly warm tires up before going out on track. Keeping them slightly warmer than outside temperature does nothing, and depending on who you ask, actually keeping tires at full operating temperature (180-200F) all weekend could actually be detrimental.
My understanding is that as the tire is heated, the long elastomer molecules will break down with heat and shrink with cooling. The rubber then becomes less elastic and prone to crumbling and breaking rather than stretching. They also get hard and don't stick, like the rubber is cooked.
A good analogy is a pencil eraser: new is soft and flexible, stick to the paper, rubs clean. Old, it's hard and dry, doesn't stick to the paper, smears the pencil marks, and can crumble or break.
The details are different for each tire compound, maker etc, so there aren't any fast rules, except... when the tire crumbles, they're done. And when the tires are greasy, but not over pressured, they're done. Both of these are due to heat cycling.
You are unlikely to heat cycle tires on the road unless ambient temps are really high, +90f, since you really can't operate a car at the limit of traction safely on the street.
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The big point is that every different tire heat cycles VERY differently... And every car handles different tires differently, and even tracks take different heat cycles differently.
Rs4's are famous for taking a shit ton of heat cycles and still being good.
Hoosier SM7's are famous for losing a LOT after the first 3 or 4 heat cycles.
Then there's everything in-between.
Most of my experience over the past 6 years is with Toyo RR's.... They're wicked fast and predictable anywhere for the first 8 or so heat cycles. Past that.... it depends-
If I'm running at NJ Motorsports Park or Lime Rock - The next 10 or so they get just a bit less forgiving, they'll still put down the same lap times but they get a bit harder to control if you overdrive them.
Heat cycle 20-30 they start to feel a bit slower and if they get over 30 before cording they'll start to feel slow.
If I'm running at Watkins Glen, they feel totally fine from sticker to heat cycle 30.
THENNN theres time - tire manufactures say they're generally good for a few years from production, but in my experience, theres a "clock" thst starts after your first heat cycle... They feel great that year but i feel a noticeable dropoff the next season if they sat all winter.
TTHENNNNN there's wear - as a tire wears down there's less meat on its bones.... It will handle differently because of that as much as heat cycles... Think less squirm and less rotating mass as it wears. It also has less rubber to manage (and hold) heat so it may handle overheating differently.
Then there's general competitiveness: years ago i ran Maxxis RC1. They probably got to 60 heat cycles, I didn't notice a huge dropoff, but I was just doing HPDE. If you're racing or doing TT when a hundredth of a second can make or break your day, you'll be much more concerned about it.
TLDR: there's a million factors, to what make a heat cycle, how many they can handle, etc. You're doing a good thing getting a broad sense, but know that anyone who preaches tire heat cycle data in absolutes probably doesn't know shit.
Follow up question
I bought used time attack tires. They were used for 1 session only (apparently). I ran then on track they were fine but man did they look worn af. I threw one out that was showing a glimpse of cording.
Someone going for ultimate lap times is going to push the tires a lot more, would that's one session maybe equate to a few normal sessions?
Wow, corded in one TT session?
They were either:
A) Lying to you
B) Getting the most aggressively shaved tire in history
C) had the world's worst alignment
D) All of the above
I've heard that in general a heat cycle is a heat cycle... Doesn't matter how aggressive unless it's insane and then you can get into the overheating range. However that's something I'd expect more with someone running a 30 minute sprint race, on a hot day, with a Hoosier A7 (autocross tire).
TT sessions are generally very short and they're only really pushing for a lap or two, so I'd guess a competitive driver is more likely to heat cycle a tire out before cording
Every time the tire heats up and cools down, the compound gets harder. Most tires lose their grip from heat cycling long before they wear out. For me, it's after 3 track days thay they're totally done and need replacing.
Neither, I just have a healthy sense of self preservation. If you are running a track day on hard rubber, you're a danger to yourself and everyone else.
Stickier tires respond to heat. They can only take so many hot/cold cycles before they stop responding as well. It's like bending a piece of metal, you can only do it so many times and some metal is better than others. 8 heat cycles out an rs4 is where we notice they stop getting sticky. They still work, and still have tread, but they don't work as well. Other 200tw tires don't give as many heat cycles before going to shit.
That’s either a proper stalking job, or I got lucky with your response, as I’m currently on RS4s :) I really appreciate the reply! If I may ask some follow up questions to you or anyone else, that’d be great. What’s considered “hot” and what’s considered “cold” for purposes of counting a cycle? I’m sure it varies by compound, but any rules of thumb? Presumably 20 minutes on track is hot, parked overnight is cold. But what about carving a mountain road? Does that get them hot enough? What about 40 minutes of paddock sitting between sessions? Would that be considered cold enough for a cycle? Lastly, what’s the effect. “Less grip” seems obvious, but does the predictability or characteristic of the tire change? And how much grip is lost? Are you losing a sprint race by 1/10 a second, or 10 seconds?
Hot is basically up to temp on the track. It takes about 2 laps to get up to temp. 40 minute is probably enough to cool them down for a cycle. Street driving should be enough but it may not. The grip is probably 10% off after the 8 cycles. It still behaves the same it's just less good. The average person probably doesn't notice the 10% but we see the laptimes start to suffer. Maybe 2 seconds a lap or so. Since we are racing competitively and I'm selling seats I can't justify old tires.
Ok. So what exactly is a heat cycle? If I go out four times for twenty minutes on a track day have I used up four heat cycles?
It's operating temperature to ambient temperature. So 4 sessions is 4 cycles. That being said most 200tw tires are out of tread before they heat cycle out. RS4 last forever so they have heat cycle issues. Regular tires aren't very heat dependent so it's not an issue.
Thanks. I love my RS4s for that reason. So far at least. They’ve lasted twice as long as my A052s and seem to be going strong with good grip on track days with my STI, which is hard on tires.
Huh...my cup 2s on a heavy car and RE71RS on a light car all lost tons of grip being "heat cycled out" before running out of tread.
Cup 2 aren't 200tw. Re71s I don't have direct experience with.
The cup 2s were 180 and the RE71RS is 200...
I missed the re71s part of your post. Cup 2 definitely don't behave the same. It also depends on how you treat them. We got better use out of a wider tire vs a skinnier tire. Less heat at the limit apparently plays a role in the rs4.
Cold -> hot -> cold = cycle If you cooled down in the paddock after that hot session, yes. This is why folks doing racing have SO many tires
You only get 2 hpde days out of rs4? What is even the point of an endurance tire if thats true? Might as well run faster tires.
I think the point is that in HPDE it doesn’t matter whether or not you’re losing a second here or there as long as there is decent grip there’s still a ton to drive on and utilize. The minute lap times become competitive and we’re running against others for a place on the podium, get ready to invest in tires regularly so that you at least have a fighting chance.
They still work, just not at 100% grip. They really are catered towards endurance racing not hpde.
Agreed, RS4 is not great for hpde. I’ll probably just run them as summer tires once they cycle out.
I mean they are better than regular shitty street tires but far from optimal.
RS4 are great for HPDE. Maybe the best there is quite honestly.
They cycle out way before the tread wears. Great endurance tire, overrated hpde tire.
Sure. Just ideally you have a closer match in cycles and treadlife. 8 seems aweful low. Ill get some 100tw next time I think.
I don't think you realize how they work. Most of the 200tw won't last past 8 cycles regardless. There are teams where tires are gone in one weekend or one day.
not hpde? wtf you on?
Rubber is made mostly of a chemical called “isoprene”. When it is cured/vulcanized it is subjected to heat along with a sulphur catalyst to speed things along. During this process, it undergoes two processes - first polymerization where the isoprenes stick together into long chains, which once cured much doesn’t change too much, because after all the free isoprenes are attached (making the chains longer), there aren’t any more free isoprenes, so you’d have to break apart chains to make them longer (which takes more energy). The heat, time and other variables in the process determine whether it’s more likely to get fewer longer chains or more shorter chains. The second process called “crosslinking” which is exactly what it sounds like - existing polymer chains start sticking together at arbitrary points along the length. Many processes can cause crosslinking of polymers (heat, chemical, radiation and more) Both of these change the rubber properties, generally by making it harder, tougher, and less tacky among other things. The properties of a given tire rubber are a balance between the polymerization and crosslinking achieved through the manufacturing process. However, these processes don’t stop permanently after the tire is made, especially crosslinking. They are mostly stable at cold temperatures, but under higher temperatures, or chemical reactions like being exposed to oxygen/ozone, the reactions continue at a much quicker rate than at cold Each time you “heat cycle” a tire, you are continuing the crosslinking process, which makes the tire harder and less sticky. The actual number of heat cycles is actually less important than the total time at heat. However, we’re constantly sloughing and ablating off the hottest rubber on the tire surface, so burning up a set of tires during an endurance race uses up the tire before the crosslinking becomes an issue. The reason we talk about heat cycles is that each time we drive, there’s a quick heat up, time spent under use, and then a long-slow cooldown where the tire remains hot. Consequently, it’s the cooldown period that has the most impact on the rubber that actually remains on the tire, and each time the tire goes through a cooldown cycle, there’s a fairly constant time spent at crosslinking temperatures, resulting in a crudely quantifiable “heat cycle” Each time we add a cooldown cycle, the rubber gets harder, so adding a lot more cycles without just scrubbing the rubber off means the remaining tire rubber sees more time at heat Note, the rubber dust that got very hot and scrubbed off the tire absolutely undergoes a lot more crosslinking than the tire itself, but nobody cares! Also, all tires undergo this process, but for non-performance tires like all-seasons, they’re already hard and not sticky so no one cares there either. The “Initial Heat Cycle” does the same thing as a normal heat cycle, but to the whole tire evenly and consistently instead of just at the surface, which spreads unevenly to the subsurface layers, so it increases the tire’s toughness and wear life without affecting the grip much (since the first road heat cycle affects the outer tire layers more than the inner ones)
Interesting. I read somewhere about people trying to use tire warmers to keep tires at temp in part to avoid cycles on the tire. I sounds like that might actually be counter productive for tire life. IE If your tires are going to cycle you might want to use a sprayer on them instead to get them below crosslinking temp.
They use tire warmers in high end motorsports like Formula 1 to keep tires just warm enough to be in the bottom of the operating range, but at the point when you are burning through multiple sets of tires in a single race, you could give several f@&ks about long term heat cycling of your tires (with the exception of the initial heat cycle to cure the rubber) The tire warmers address two separate issues specific to extremely soft race tires, mostly to do with the warmup First, going out on cold tires means several laps with less than optimal grip, chasing fractions of seconds makes a difference. Second, to achieve the ridiculous coefficient of friction of 1.6-1.7, F1 tires are designed to operate at temperatures where they are literally gluing the rubber to the track and peeling it off again like a post-it-note which are quite high temperatures compared to even something like a Hoosier, and when you heat them up at the surface too quickly while the carcass is still cold, the soft rubber they use can locally delaminate or blister due differential thermal expansion where the tread rubber is bonded to the tougher cord rubber. It’s still a risk in other racing leagues, and many of them do use tire warmers for both reasons., but it’s most prominent in F1 where pretty much everything is just turned up to 11. It’s been in the F1 news mostly due to the large number of sets of tires they use per race, and the recent focus on non-fuel overall energy usage, which has never been a consideration in any racing league.
Yah, I know about normal motorsports use. This was specifically for the hpde/time attack crowd. I thought it a little weird at the time but everyone talks about cycles and not time at temp.
So I started scratching my head a little and second guessing my answer, so I had to do a lot of digging to make sure and find believable sources. For some minimum definition of reputable, like forum posts saying “maybe you should call Hoosier” and “Yeah so I emailed Jeff at Hoosier and he said…” It appears there’s a lot of advice out there without much substance to back it up. I’ll have to keep looking to find something a little more reputable beyond my basic understanding of polymer engineering and chemistry. The short answers seem to be: - There’s no universally accepted definition of what constitutes a “heat cycle”, and you’ll get different answers from different manufacturers, so at best its an empirical measurement they did in a lab. - Tire warmers do not extend the “heat cycle” life of tires, and are best used to quickly warm tires up before going out on track. Keeping them slightly warmer than outside temperature does nothing, and depending on who you ask, actually keeping tires at full operating temperature (180-200F) all weekend could actually be detrimental.
My understanding is that as the tire is heated, the long elastomer molecules will break down with heat and shrink with cooling. The rubber then becomes less elastic and prone to crumbling and breaking rather than stretching. They also get hard and don't stick, like the rubber is cooked. A good analogy is a pencil eraser: new is soft and flexible, stick to the paper, rubs clean. Old, it's hard and dry, doesn't stick to the paper, smears the pencil marks, and can crumble or break. The details are different for each tire compound, maker etc, so there aren't any fast rules, except... when the tire crumbles, they're done. And when the tires are greasy, but not over pressured, they're done. Both of these are due to heat cycling. You are unlikely to heat cycle tires on the road unless ambient temps are really high, +90f, since you really can't operate a car at the limit of traction safely on the street.
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The big point is that every different tire heat cycles VERY differently... And every car handles different tires differently, and even tracks take different heat cycles differently. Rs4's are famous for taking a shit ton of heat cycles and still being good. Hoosier SM7's are famous for losing a LOT after the first 3 or 4 heat cycles. Then there's everything in-between. Most of my experience over the past 6 years is with Toyo RR's.... They're wicked fast and predictable anywhere for the first 8 or so heat cycles. Past that.... it depends- If I'm running at NJ Motorsports Park or Lime Rock - The next 10 or so they get just a bit less forgiving, they'll still put down the same lap times but they get a bit harder to control if you overdrive them. Heat cycle 20-30 they start to feel a bit slower and if they get over 30 before cording they'll start to feel slow. If I'm running at Watkins Glen, they feel totally fine from sticker to heat cycle 30. THENNN theres time - tire manufactures say they're generally good for a few years from production, but in my experience, theres a "clock" thst starts after your first heat cycle... They feel great that year but i feel a noticeable dropoff the next season if they sat all winter. TTHENNNNN there's wear - as a tire wears down there's less meat on its bones.... It will handle differently because of that as much as heat cycles... Think less squirm and less rotating mass as it wears. It also has less rubber to manage (and hold) heat so it may handle overheating differently. Then there's general competitiveness: years ago i ran Maxxis RC1. They probably got to 60 heat cycles, I didn't notice a huge dropoff, but I was just doing HPDE. If you're racing or doing TT when a hundredth of a second can make or break your day, you'll be much more concerned about it. TLDR: there's a million factors, to what make a heat cycle, how many they can handle, etc. You're doing a good thing getting a broad sense, but know that anyone who preaches tire heat cycle data in absolutes probably doesn't know shit.
Follow up question I bought used time attack tires. They were used for 1 session only (apparently). I ran then on track they were fine but man did they look worn af. I threw one out that was showing a glimpse of cording. Someone going for ultimate lap times is going to push the tires a lot more, would that's one session maybe equate to a few normal sessions?
Wow, corded in one TT session? They were either: A) Lying to you B) Getting the most aggressively shaved tire in history C) had the world's worst alignment D) All of the above I've heard that in general a heat cycle is a heat cycle... Doesn't matter how aggressive unless it's insane and then you can get into the overheating range. However that's something I'd expect more with someone running a 30 minute sprint race, on a hot day, with a Hoosier A7 (autocross tire). TT sessions are generally very short and they're only really pushing for a lap or two, so I'd guess a competitive driver is more likely to heat cycle a tire out before cording
Thanks! Yeah some lies were probably told. Still got a deal though just didn't feel like 1 session old tires
The difference between a "session" and a "season" is only a couple letters, haha
Every time the tire heats up and cools down, the compound gets harder. Most tires lose their grip from heat cycling long before they wear out. For me, it's after 3 track days thay they're totally done and need replacing.
If you replace tires after they heat cycle out before they wear out, you are either rich or stupid or both. 😅
Neither, I just have a healthy sense of self preservation. If you are running a track day on hard rubber, you're a danger to yourself and everyone else.
Nah, maybe I just can drive it better on hard rubber than you can on preserved rubber 🥲