Track Tire Heat Cycle
A new set of tires arrives at your doorstep, and it’s a beautiful sight and oh the smell of fresh rubber! Most people who are not involved in motorsport racing just can’t comprehend how wonderful new tires are. To them, they are merely rubber tires that appear to be worn well past their useful life. For us racers, they represent so much more and are one of the key components to our success. The good news is you can extend the useful life of motorsport track tires by following an initial heat cycling process, which is sometimes referred to as scrubbing.
Heat cycling race tires breaks the uneven bonds of a new tire and allowing them to reform in a more uniform manner. As a result the tire compound is stronger thus more resistant to wear and handles more consistently throughout a track session.
Tire Break-in Procedure
Proper break-in will not affect initial performance but will increase the competitive life of the race tire. The procedure can be broken down into phases;
1st phase: The initial heat cycle
2nd phase: Cure time
The Initial Heat Cycle
The first laps for the track tire are critical for setting up the durability and competitive life. The first session should consist of no more than 10-15 minutes of running. The early part of the session should be run at an easy pace, with the speed gradually increased until the end of the session. The final lap should be run at the fastest possible speed. The intent is to achieve maximum tire temp on the last lap. At this point the car should be brought in and the tires allowed to cool at a normal rate.
During the initial run-in process, the inflation pressure should be 3-5 psi higher than you would normally use. The best progression would have the driver taking 4-7 laps to accomplish this break-in. Each lap should be approximately 7-10 seconds a lap faster than the previous lap. The goal is to have the tire temp as high as possible on the last lap without “shocking” the tire during the warm up laps. The last lap should be at, or very close, to the maximum possible speed.
For autocross, the A6 r-comp performance tire does not need the same break in procedure as the R6. The A6 needs a minimal scuff-in session before the first autocross run. This session can comprise of simply driving around the event site at minimal speeds on the A6 set of track tires. By scrubbing off the newness of the tread (no or minimal shininess remaining) prior to your first competitive run, the A6 track tires will be more consistent in handling, grip and responsiveness on the first run. If this is not completed, running on un-scuffed A6 tires on your first run may result in the tires not gripping properly, or feeling like they “skate” over the course surface. You are welcome to run 3 - 5 psi higher than normal when scuffing in a new set of A6’s, but be sure to reset them to the correct operating pressures before your first autocross run. As you compile autocross runs on your new A6’s, they should become more consistent in run times.
After completing the initial run phase, the length of time the race tire is allowed to set is possibly more important. The barest minimum for this process to be beneficial is 24 hours. (Not “the next day”). Any less than this is a waste of time. The best situation would allow a week before using the tire again.
Proper track tire management is a difficult process. To accomplish this almost always requires a second set of wheels. The payoff is greatly increased competitive track tire life.
Following the recommended break-in procedure will require a lot of planning to make it work. The benefits to doing it right include greatly increased track tire life as well as consistent performance and durability under stress. Please make an effort to educate your motorsports team on the importance of this. It can save you a lot of money.
Heat Cycle Chemistry
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 race 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.
So then, what happens in a heat cycle that can improve the performance and durability of your brand new tires? Well, actually, the situation described above is the first step in the heat cycle process. You want to break all of those "uneven" bonds. 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. The bonds will still break if you exceed the limits of the compound, (both mechanical and thermal). 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 tires must be allowed relax for an absolute minimum of 24 hours after that initial heat cycle. 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.
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