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 hrs 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.

Discount Tires explanation

A competition tire is built with a highly sophisticated tread compound. This compound is capable of sustaining traction throughout a much wider temperature range, but is also extremely sensitive to the first heat cycle of its use. During this cycle, if controlled precisely, the tread compound stretches as it heats, breaking the weaker, shorter molecular bonds within the rubber. The benefit of this process is a tread compound that lasts longer and provides better traction. However, if the first cycle is not performed correctly, the tread may develop irregular compounding, leading to poor wear and inconsistent traction.

Jamie’s best description – he worked as a Tyre Manager for RED BULL F1 TEAM

Heat cycling, basically changes the cross links between the long polymer chains within the rubber. Imagine a bathtub full of snakes. The chains of the polymer are like the snakes. Sulphur acts as a cross linking molecule within the rubber.These cross links reduce the ability of the chains to slide one across the other, hence it it like linking the snakes. This is the process that reinforces the rubber, stiffening it without making it brittle. Natural rubber is very soft, imagine your pencil eraser and you are not far away.

Putting energy in through heat cycling increases the molecular movement and excitation atomically within the polymer, hence making it possible for some extra cross links to form once the rubber starts to cool.So it is not about long chains or short chains. Molecular bonds are limited by the atoms concerned, you don't get long or short bonds (unless single,double or aromatic bonds (don't ask)) you get long, short and cross linked chains.

Rubber is all about grip, and grip related to hysteresis. Have you heard about that?

Therefore as you reduce grip you may reduce wear, until you go to hard and the rubber shears. The crosslinking and resturcturing of the polymer bonds through heating or scrubbing has been known for years. It will reduce the inherent grip and should normally increase the first lap time (by reducing the inherent hysterisis of the compound hence the grip). With some less exotic compounds the curing will increase the resiliance/endurance of the compound. Scrubbing (e.g. running the tyre on the track) will increase this crosslinking and polymer resiliance, however the running of a tyre on a rough surface will rough up the surface of the tyre, reduce the actual surface area, and hence reduce the number of contact points. This is the most likely reason for the time difference between a new and a worn tyre

 
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