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Locked[FAQ]Competition Tyre Heat Cycling Explained

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2013/11/17 11:02:20 (permalink)

Competition Tyre Heat Cycling Explained

Heat Cycling explained
Let's look at what a heat cycle is, and what it does to the tire. We will concentrate on the tread compound, but there are similar benefits for the other compounds in the tire 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 high school chemistry classes, the molecules that make up polymers are long chains of atoms. To kind of 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 tire 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 tires "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 tires 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 tires are run. That doesn't mean that you can't make the tires 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. In the case of the R1, the tires must be allowed relax for an absolute minimum of 24 hours after that initial "break in". I will sometimes tell people to wait up to a week to be sure. But we really haven't seen any additional advantage to waiting any longer than that. If you don't give the tires enough time to reform those bonds though, then you are going out on tires 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 tires.
Let's talk now about the number of heat cycles you can expect out of a tire. I've heard people talk about Brand-X, or Brand-Y, or Brand-Z tires only being good for X number of heat cycles. We really have not seen this with the Comp T/A R1. You should be able to expect the same performance level from the tire 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 tire "harder". The tire 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 R1's. The first heat cycle is the most critical. Subsequent heat cycles do not cause any detriment to the performance of the tire. It is still possible to overheat heat cycled tires. 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.
Tire Rack explanation
The first time a competition tire is used is the most important. During that run, its tread compound is stretched, some of the weaker bonds between the rubber molecules will be broken (which generates some of the heat). If the tires are initially run too hard or too long, some of the stronger bonds will also be broken which will reduces the tire's grip and wear qualities. Running new tires through an easy heat cycle first, and allowing them to relax allows the rubber bonds to relink in a more uniform manner than they were originally manufactured. It actually makes them more consistent in strength and more resistant to losing their strength the next time they are used. An important heat cycling step is that after being brought up to temperature, the tires require a minimum of 24 to 48 hours to relax and reform the bonds between their rubber molecules.
How to do it
Note that this is just a guideline, as this isn't an exact science!
  1. Start off with around 25 or 26 psi cold and get some heat into the tyres. Within 2 minutes of coming off the track bleed back the tyres to 30 psi (hot pressure).
  2. When hot pressure is set, do 3 or 4 laps at 95%, drive smooth, no lock up of brakes or sliding.
  3. Leave tyres for 2 hours minimum or preferably overnight.
It is best to store your tyres off the car and out of ultraviolet light to get the best use and service out of them.
post edited by Admin - 2013/11/22 18:07:56

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