Race Car Tire Pyrometer
Featured photo by Alex Valenze. All other images by Brian Smith.
Since skipping my college graduation to buy a racing kart, I’ve raced a variety of cars over the years — sprint and enduro karts, Formula V and Formula Ford, and now SCCA Solo (autocross) with a Toyota MR2 and a BMW Z4. All very different cars with one thing in common — tires.
Ultimately, tires determine how much grip is available for the driver to use for acceleration, braking, and cornering, so knowing their condition is an important data point for optimizing car and driver performance. In this project I’ll show how to measure and log your tire temperatures with a DIY recording tire pyrometer based on a cheap ESP32 microcontroller.
If racing’s not your passion, you can use this project as a basis for all kinds of compact, portable data recorders by changing the attached sensors. Want to get soil moisture measurements from your garden? GPS positions? Sound volume? Light brightness? Air quality? Any sensor that has an I²C or SPI interface and an Arduino library is easy to add to this basic design.
What Tire Temperatures Tell You
When talking about tire temperatures, racers refer to the inside, outside, and center of the tread. The grip available from a tire depends on how much of the tire is in contact with the ground, and the vertical force or load applied to the tire. Ideally, you want to set up the tires and suspension so the load across the tread is as even as possible, generating the most grip.
If the air pressure is too high, the contact patch shrinks as the tread crowns at the center of the tire. Too low, and the inside and outside edges of the tire do more of the work because the sidewalls are supporting more of the load. As tires heat up, so does the air inside them, so you may need to start a session with lower than ideal temperatures. Measuring temperatures and air pressures at the end of the session helps you find the right air pressure for each tire at the start.
Tires generate grip from friction, and friction generates heat. So measuring the temperature of each tire at inside, center, and outside points tells you how hard each part of the tire is working to generate grip. Ideally the temperature across the tread should be consistent, and in the best working range of the tire. If it’s above or below optimal, you get less grip. Too cool? Maybe switch to a softer tire for more grip at lower temperatures. Too hot? A harder compound tire gives more grip at higher temperatures.
It’s possible to take tire temperatures even while the car is in motion using non-contact IR thermometers. But tire pyrometers have a tire-specific temperature probe that pushes into the tread to get a more accurate temperature. With a few easily available parts and some soldering skills, you can build a recording tire pyrometer that has more features than commercially available pyrometers costing several times more.
Recording Tire Pyrometer Design
The RTP’s functions define the hardware needed:
- Read and display tire temperatures: K-type tire pyrometer probe and K-type thermocouple amplifier; TFT display for visibility outdoors
- Record temperatures: microSD card
- Access the web for setup and to display results on phones/tablets: ESP32 microprocessor
- Timestamp results: real-time clock (RTC)
- Handheld unit: 3D-printed enclosure suitable for outdoor use
- Support multiple car/driver/wheel configurations: simple, fast user interface
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