Internal vs External Tyre Temp

Hi guys

I'm looking for some TPMS and Tyre Temp sensor solutions. I saw some from Izze Racing that are a single unit mounted inside the rim that has both pressure and internal tyre temp across the face.

I guess the question is how useful is internal tyre temp vs external.

Hi Adrian,

This is quite a long topic to get into, but an interesting one.

There are 3 main types of live tyre temps measurements

-Internal "air" temp

-External IR

-Internal IR

I find the internal tyre temp you get from mot motorsport TPMS systems useful for understanding the relative energy distribution between each of the tyres at each track and also for helping me get the hot pressures right - we're essentially estimating the internal air temp with the measurement. It's estimating because it tends to be quite influenced by rim temp.

External IR is helpful for understanding how the energy is being distributed over the surface of the tyre. We can use this to help tune tyre pressure and wheel alignment. Some downsides are that they can be challenging to fit while working properly. Especially on the front wheels with them being turned during cornering, if we want to keep them looking at the same parts of the tread, the sensors really need to be mounted to some part of the hub. This is a pain and often means you only test with them rather than having them on the car for races.

Internal IR is reading the carcass temp. In my opinion, this is probably the most useful for tuning the car and understanding how the tyre is working. It is giving similar info to the external tyre temp by instead we are understanding how the construction of the tyre is being loaded which I think is more useful than knowing how hot the tread is. It also helps that it's built into the sensor so nothing to mount externally.

Why not all? Other than the cost that is.

I have the IZZE external sensors (16ch, because, why not) on my car and they work well. They can even pickup the temperature change from a lockup which the internal units will not.

I can see a value in both (probably why FI uses internal and external sensors) in that the internal sensors give data of how the tyre carcass is heating. This allows the driver/engineer to check that there is not too much heat being put into a particular region of the carcass as this can lead to blistering of the tread and/or tyre failure. The external temperature sensors will tell you how the tyre is working in transient conditions.

In one of the videos that Caleb from IZZE Racing has posted, you can see the effect on the tyre surface temperature that the exhaust pipe location (just in front of the LH rear wheel) has, with the surface temp increasing whilst going along the straight. This could lead to a handling imbalance at the next corner as one tyre has a higher tread temperature than the other.

Hey Stephen

Cost is the answer to your question. The simplicity of the internal IR is appealing but it seems you miss all the transient info.

Tim, Stephen

If the main use case is optimising tyre pressures and alignment geometry: how would you rate the usefulness of both the internal vs external IR sensors out of 10?

I would still count internal IR as a transient measurement, it's true that it may not react quite as quickly as external IR. However, in my experience, the internal temperature spread of the carcass correlates more closely with setup and performance than external IR.

We have actually bought some Izze products that we are planning to fit to one of our cars and do some testing with this year- both TPMS and external IR, it will be interesting to see how this goes.

I would say external IR 7/10 and internal IR 9/10. In saying that, it will be interesting to do some more work in comparing them more directly.

Thanks Tim

Should the last sentence above say "However, in my experience, the internal temperature spread of the carcass correlates more closely with setup and performance than internal external IR.

Thanks for catching that Adrian, edited the original post to correct it 🙌

Hi Tim,

Have you done any more work since comparing internal vs external IR sensors?

Hi James, Tim has actually moved on and doesn't work for HPA any more. That being said I have now spent quite a lot of time with the internal and external data. I find the external data to be more useful to validate setup changes as you get a much faster response from the sensor during cornering. Obviously there's a latency in terms of the heat transfer from the tread contact patch (what we're really trying to optimise) and the temperature in the carcass.

While the internal TTPMS sensor is a nice neat single point solution and much easier to mount than external sensors, if I was to pick only one it would be external every time. Hope that helps.