Tire Temperature and Pressure
Coming soon! An online tire temperature analyzer tool to troubleshoot setup problems based on post-stint tire temperatures. Stay tuned and check back often for updates!
Tire pressure is critical to the tire’s performance (grip) as well as ride heights.
Tires that heat up unevenly can affect your wedge and roll couple distribution, creating some uncomfortable long run situations. It is therefore an important part of setting up your chassis to balance wear on the tires, as this is what determines “hot pressures” (how high the tire pressures go during the run). For example, a right front tire that heats up to 63.5 PSI when the right rear only heats up to 62.0 PSI has the same effect on the chassis as installing a stiffer spring on the right front: It increases wedge, which renders the car “tight.” You would either loosen the chassis to put more workload (and heat) on that right rear in this case; or adjust tire pressures by adding air into the right rear and/or taking a little out of the right front (both of which, ironically enough, will loosen the chassis; one of those setup building situations where the cure to a problem double-dips).
Tire Pressures
Before setting permanent tire pressures, make sure all your chassis adjustments are pretty much locked in. Changing your chassis setup will require tire pressures to be revisited. Until your chassis setup is very close to final, tire pressures and temperatures should be used as diagnostics rather than a setup component.
| Condition | Correction |
|---|---|
| More wear in middle than on edge(s) | Increase tire pressure |
| More wear on edge(s) than in middle | Decrease tire pressure |
| Left front tire pressure is more than 1.5 lbs. different than left rear | Divide the difference by 2, then add/remove pressure as appropriate to balance |
| Right front tire pressure is more than 1.5 lbs. different than right rear | Divide the difference by 2, then add/remove pressure as appropriate to balance |
Start by addressing over/underinflation issues first, then go for pressure balance. Remember to reset the ride heights after changing tire pressures.
With respect to ride height, tires act like springs:
- Higher tire pressure increases heat tolerance, decreases mechanical grip, makes the chassis stiffer, raises the ride height, and increases the corner weight at that corner (which affects wedge, cross-weight, and the roll couple distribution), and decreases its temperature.
- Lower tire pressure decreases heat tolerance, increases mechanical grip, makes the chassis softer, lowers the ride height, and decreases the corner weight at that corner (which affects wedge, cross-weight, and the roll couple distribution) and increases its temperature.
However, the effect of tire pressure on the chassis is different from that of spring rates:
- Higher right-side tire pressures loosen the car.
- Lower right-side tire pressures tighten the car.
- Lower left-side tire pressures loosen the car.
- Higher left-side tire pressures tighten the car.
The effect of tire pressure on the left-rear is greater under acceleration:
- Higher left-rear tire pressure tightens the car under acceleration (middle turn and exit).
- Lower left-rear tire pressure loosens the car under acceleration (middle turn and exit).
Tire Temperatures
Tire temperatures are tell-all when it comes to the chassis changes you need to make. The outer, middle, and inner temperatures can be used to determine incorrect wedge, tightness, looseness, under- and over-inflation, and many other factors. Depending on the severity of the average temperature differences, tire temperatures can help you fine tune a setup or isolate and correct glaring deficiencies.
Tire Temperature General Guidelines
- The average temperature of each tire should fall between 190-240 degrees F.
- The right front tire should be no more than 10 degrees F. hotter than the right rear.
- The hottest tire is the most worked.
- The coldest tire is the least worked.
- The average temperature the farthest away from optimal (either colder than 190 F. or hotter than 240 F.) is the first corner of the chassis you should work on.
Tire Temperature Setup Procedure
The following procedure will have you drive your car for 15 miles (usually 10 laps) before analyzing tire temperatures and making adjustments for: cambers; pressures; toe-ins; wedge; tight-or-loose conditions; and over- and under-worked tires.
Tire Temperature Analysis
Cambers
Consider the front tire temperatures in the garage, post-stint.
| Inner | Middle | Outer | Condition |
|---|---|---|---|
| (hottest) | (cooler) | (cooler) | Excessive negative camber |
| (cooler) | (cooler) | (hottest) | Excessive positive camber |
Tire Inflation
Consider each corner tire temperature in the garage, post-stint.
| Inner | Middle | Outer | Condition |
|---|---|---|---|
| (cooler) | (hottest) | (cooler) | Over-inflated tire |
| (warmer) | (coldest) | (warmer) | Under-inflated tire |
Toe-In
Consider the front tire temperatures in the garage, post-stint.
| Outer | Middle | Inner | Inner | Middle | Outer | Condition |
|---|---|---|---|---|---|---|
| (cooler) | (cooler) | (hottest) | (hottest) | (cooler) | (cooler) | Excessive toe-out (negative toe) |
| (hottest) | (cooler) | (cooler) | (cooler) | (cooler) | (hottest) | Excessive toe-in (positive toe) |
Wedge Computations
To check wedge by tire temperatures, you must know how to calculate the average tire temperature: Add the outer, middle, and inner temperatures together and then divide by 3:
avg = ( o + m + i ) ÷ 3
Then, add the averages of the two tires together and then divide by 2:
cross-weight-average = ( avg[left-rear] + avg[right-front] ) ÷ 2
front-average = ( avg[front-left] + avg[right-front] ) ÷ 2
right-average = ( avg[right-front] + avg[right-rear] ) ÷ 2
Your car has excessive wedge if cross-weight-average is the same or higher than both front-average and right-average.
On the other hand, your car has insufficient wedge if cross-weight-average is more than 10.0 degrees cooler than both front-average and right-average.
Tight/Loose Computations
To compute a tight or loose condition based on tire temperatures, you will need the tire temperature averages that you used to detect wedge problems, above.
| Temperatures | Condition |
|---|---|
avg[right-front] is more than 10.0 degrees hotter than avg[right-rear] |
Tight |
avg[right-front] is more than 10.0 degrees cooler than avg[right-rear] |
Loose |
Over- and under-worked tires
Over- and under-worked tires are easy to spot by looking at the averages. The average tire temperature should be 190-240 degrees F. after 10 laps on the track. Any tire that is hotter or cooler than that should be corrected.
- If a tire is overworked (hotter than 240 F.), it should have weight taken off it to reduce its workload.
- If a tire is underworked (cooler than 190 F.), it should have weight transfered to it to increase its workload.
It is usually at this temperature-testing stage of the setup that you discover ride height and spring setups have issues and have to be corrected. You will need to likely go back to earlier steps involving ride heights and spring rates to fix tire workload issues. Of course, that starts the whole process over again; starting right with the simple cambers and tire inflations and working your way on down again. While it can be frustrating, patience, perseverance, and persistence will lead you to success. Don’t give up!