Tires are the most important part of any vehicle
I wanted to investigate moving from 18” to 16” low profile tires. There were several 16” tires to choose from, so before arriving at my decision I had several hypotheses and questions to answer.
Key Questions to Answer
Will grip be much lower?
Will we have issues with tires overheating?
How will the change affect driving feel?
Lower rotational inertia
Lower unsprung mass
Faster warmup time
Less rubber: Less overall grip
Smaller volume: More pressure variation with temperature
I started by analyzing data presented to all FSAE teams that buy into the Tire Testing Consortium (TTC). I compared warmup time, the ultimate grip, camber sensitivity, and cornering stiffness of 4 different low-profile tires. Several examples of plots are below. Based on this analysis tire B (see Figure 2) was selected as the best option of the 4 presented.
Tire B appears to warm up the quickest and maintains a steady temperature as the test progresses.
The grip between tire B and our previous 18” tire appears similar.
Once I was convinced that tire B from above was likely the best choice, I went ahead and ordered a full set to perform our own testing. This was in July of 2019, and so the 2018-19 vehicle was still operational and being used as a test mule for the upcoming build cycle. The goal of performing our own tire testing was to verify that the data from TTC was representative of actual performance, and that nothing major had been overlooked in the selection process.
We set up a test track representative of the skid pad event at competition and performed back to back comparisons of the old 18” tires, and the new 16” tires. Both sets of tires were brand new, and we documented temperature and tire pressure after each lap.
During the testing of the new tires, we placed the fastest skidpad of the year. Between those impressive results and the fact that the tires stabilized at a reasonable operating temperature, despite repeated back to back runs and relatively warm weather into the afternoon I was confident in my decision to move forward with the remainder of the suspension design. Feedback from the drivers was also positive, saying that the tires were more responsive and the car easier to control.