Arrr heat cycles! One of the most common discussions you might hear about tyres is to do with heat cycles. This article shares my thoughts and experience on heat cycles and a few methods you can use to better determine when to replace your tyres.
Buy New Tyres Every Session (or Not!?)
If you have an unlimited budget for new tyres then you can stop reading now.
Newer tyres simply give you more grip. The end š
But, back in the real world…
You might be thinking about how you can get the most out of the tyres you do have?
Your goal therefore becomes how many heat cycles can you get away with before you need to replace them.
If that is you… read on my friend.
What is a Heat Cycle?
Ok, determining what a “heat cycle” really is, is not super clear. It tends to go a little like this.
- In the pits your tyres start out at the ambient temperature.
- When you take them on track they heat up with use.
- Then, when you come off track they cool back down.
This process of heating up your tyres and cooling them back down again, is known as one heat cycle:
The definition is imprecise because no-one really states how hot, or for how long, your tyres need to experience this to make up 1 heat cycle.
In practice, this doesn’t always matter.
As long as your track sessions are similar each time, you can say the number of heat cycles is the same as the number of track sessions you have.
Why are Heat Cycles Important?
Why heat cycles are important is because each heat cycle is wearing out your tyres thermally.
Each heat cycle causes a relatively big change in the arrangement of the molecules in the rubber. In the end, and a load of chemistry later, this means your tyres look like they have dried out.
Here you can see what my tyres look like when they are new and when they are old:
Whilst your tyre might look like it has a decent amount of tread left on the “old” one, the result of multiple heat cycles means it has less grip.
Here the old tyre has about 15 heat cycles and is starting to look fairly well used (you might need to zoom in to the shoulder to see.)
This is verses the new one that has had just one heat cycle.
You can also compare the appearance of the tyres. The tread on the new tyre is slightly different in colour and texture – with the newer tyre more matt and dull in appearance.
Next time you get a new set of tyres, keep an eye on this surface texture evolution, as well as the amount of tread wear.
Tyre Compounds and Heat Cycles
My experience is that most tyres normally have quite a large drop off in grip over the first few heat cycles.
What happens then depends a lot on the type of tyre compound you have.
A pure race tyre might be done after only a handful of heat cycles.
With a more road-focused tyre, you might expect the grip to plateau for a while and then eventually drop off.
As annoying, and expensive as it is, there is little getting round the benefits of new tyres in terms of grip.
Keeping Track of Your Tyres’ Heat Cycles
I’ve found it useful to keep a basic record of each run you have on a set of tyres.
With this information, you can then try and work out a reasonable “life” for your tyres, in terms of heat cycle and lap count, to match your budget and aspirations.
With the tyres we used in the research of the tyre course, I was trying to see how far we could go.
I got 30 heat cycles out of them before they really, really noticeably died.
Looking back through the records there was actually a noticeable drop off at between 20 and 22 heat cycles.
Going forward, for those tyres we would therefore be looking at a 15 to 18 heat cycle “life.”
I suggest this is the mental model you want to populate for yourself, given your car and situation.
For example, I was recently coaching a guy in a single seater who runs on slicks. His tyres had a much lower heat cycle window – something like 4 to 8 heat cycles.
Putting on new tyres also came with a huge benefit to him, often over 1 sec per lap.
The challenge then became one of being strategic on when to use new tyres (Ā£3000 per set!!) and when you could run a session with older rubber.
It is not always easy but if you have a limited budget then this is what you can expect.
3 Ways of Working Out If Your Tyres Are Heat Cycled Out
You might be wondering how you know if your tyres are getting worn out, especially if tread wear is not the only factor.
Your tyres are going to wear out so here are 3 ways to try and work this out.
It is imprecise, as the answer is “buy new tyres always” so my aim with this is simply to help you maximise your return on investment.
1 – Driver Feedback
Firstly, as a driver and as you get more experienced, you will soon feel the difference of the lower grip.
Well, in my experience, you actually soon feel the difference that new tyres give you.
Therefore, in your driver feedback notes make sure you are commenting on your grip.
Over time your goal is to be able to determine the shape of your tyres grip life curve. In other words, determine how many heat cycles you will typically have left before you need to replace your tyres.
In your notes, consider the grip under braking, the transition into the corner, at mid-corner and when you are exiting the corner.
Ask yourself, how much grip do you feel you have?
Ok, yes, this approach is not super precise but I feel it is important to get you as a driver aware this will be changing.
2 – Use Your Data System
Another option, if you run any kind of data system, is to keep an eye on your peak and average acceleration values over each session.
This can start to give you an idea of tyre status more objectively verses pure feeling.
The acceleration your car can develop is limited by your grip. If your grip is reducing then the level of acceleration your car can generate will also reduce.
Your challenge with this is that it might not be clear what is causing the changes in the values.
However, if you take a look over several sessions, you can sometimes see a sessions average acceleration drop away.
Whenever I think about using performance data more statistically I think of Jorge Segers.
If you have not got his book you might want to check it out.
You can also listen to how he approaches data analysis in a refreshing way when he joined me on the podcast show.
3 – The Durometer…
Another popular method you might hear people talk about is using a durometer.
This is a device that measures the shore hardness of the rubber.
It is an interesting topic as the shore hardness does have an influence and can certainly change with each heat cycle.
Each cycle increases the shore hardness and, the theory says, reduces your grip.
One issue you might have is that, I’m not sure you are going to be able to measure the small differences reliably enough on a durometer with your tyres.
By all means, gather this data if you can. But, if it is a choice of durometer data or say tyre temperature data, then without question I would recommend prioritising the tyre temperature data.
Heat Cycles In Summary
Ok, so now you have more of an understanding for heat cycles.
You also have a few methods to help you determine when it’s time to replace your tyres.
Remember, newer tyres simply give you more grip, and the number of heat cycles on your tyres can have a significant impact on their performance.
Keep an eye on the surface texture evolution, as well as the amount of tread wear, and use your driver feedback notes and data analysis to help you determine the “life” of your tyres.
With this information, you can make strategic decisions about when to replace your tyres and maximise your return on investment.
If you have any experience you want to share on heat cycle management, be sure to sign up to Ahead of the Curve below and let me know. You’ll also get all the latest articles so never miss out.
