Measuring tire surface temp to set pressure

[gmcman]

I figured I would try this since I just picked up a new set of shoes. My last set I kept at 36 PSI and I have these Conti's set at 34 PSI cold right now. My drive home was 30 miles of hwy with few stops and no hard turns. I used an infrared gun when I got home and the fronts were 92-93 deg on the edges and 88 deg in the center....same for both fronts. Rears were 91-92 on the edges and 88 in the center.


I will up the pressure 1 PSI in the morning and check again when I get home. Curious to see if they eventually even out. I have given the tires about 250 miles of break-in and the alignment is good.

 

[DucatiSS]

What was the air pressure when they were hot/warm?

Is the edge temp suppose to be the same as the center? Is the amount of rubber the same on the edge vs. the center? Would that have any bearing on the temps?

Interesting test

 

[Chickenhawk]

Measuring tire pressure across the tread (inside edge; center; outside edge) in three different spots around the tire is an excellent way to find out optimum pressure for traction, and can detect problems with dynamic balance, caster, camber and toe-in. It is a technique that is commonly used in race cars for years.

Just be careful that you are not reading too much accuracy into an infrared gun. Race teams actually use a sharp temperature probe inserted into the tread to measure temperature to a tenth of a degree.

And, yes, in an ideal setup, the temperature would be consistent across the width of the tread for maximum traction.

Comparing side-to-side temps can also show how it potentially corners and comparing back-to-front temps can show excessive understeer or oversteer.

A couple of hot laps and then a chart of tire temperatures across the total width of the tread, measured on three different places on each tire, can show a LOT about the handling of the car.

Race car driver extraordinaire Mark Donohue was an engineer first, and who could tell more about the handling of a 220 MPH race car doing a couple of laps around a tight skidpad going 20 MPH than any other person on the face of the earth. He used tire temps extensively to set up his race cars, and his dominance as a driver, engineer and tactician overwhelmed other teams and basically shut down the Can-Am race series of the 1970's.

All that being said, it may be a bit of overkill for a 5000 pound SUV driven on the street ... but it IS fun to learn how to optimize the tire patch for maximum traction and how to use differential pressures to help balance the handling of a street car.

 

[gmcman]

What was the air pressure when they were hot/warm?

Pressure when I checked the temp was 36, however it was believed the cold pressure was set at 34 by the shop when I had the tires installed, I was thinking that 2 PSI was a small jump for a warm tire. Very well could have been but when I checked them the next morning they were at 32. This easily could have been the difference from mid-day to early morning ambient temps...so temp change was 4 PSI which is normal.

Is the amount of rubber the same on the edge vs. the center?

I would speculate yes since they are new but after 250 miles I would hope any small ridges should be at least worn somewhat even...or hope so.

Just be careful that you are not reading too much accuracy into an infrared gun. Race teams actually use a sharp temperature probe inserted into the tread to measure temperature to a tenth of a degree.

The reading from the IR gun was jumping a little but I averaged the temp the best I could, the second test I used my temp probe from my Fluke meter and it was much more stable. I rounded the temps slightly unles they were at .5 but most were +- .2 of a whole number. I checked temps with the IR gun as well and the temps while were as consistent...were about 1.5-2 deg higher, temps shown were from the Fluke probe.

The second test I set the cold temp in the AM at 35 PSI for all 4 and checked when I left work.....pressure was the same. I was on the interstate for about 40 miles and when I came off the exit, I checked the pressure and was at 38 PSI for all 4. Trying to get home to see the kids so I didn't take a temp reading.

Upon reaching the house, I checked the pressure and it was down to 37 for all 4 and I probed the tread about 1/8" deep.....results were interesting.

The right rear has more negative camber and more toe-out, resulting in the inside of that tire to be the warmest. The fronts both were warmer on the inside but not much. The RF caster is out so I suspect the ball joints could be the culprit, camber was in spec but different from the left.

Granted I need to take more readings and average them out but for a preliminary test it's a good start. I want to say the axle bearings may be worn to give the different alignment values and I do remember a very small amount of play in the bearings last time I checked....didn't think they would change the angle as much as they have...unless there is another problem.

Here are the temps when I arrived home, I also added the alignment report.

-------------------LF---------------------------------------------RF----------------------------
-----------84------80-----88------------------------------85-----82-----83
>
>
>
>
>------------------LR---------------------------------------------RR-------------------------------
>----------83------82-----88------------------------------89-----85-----84-------------------

 

[Chickenhawk]

What are you using for tires?

I would bump up 1 more PSI cold in the fronts and see how it feels.

 

[gmcman]

I'm running the Continental Cross Contact LX-20. Enjoying them very much right now....roughly 70/30 Hwy/Cty and i'm at 19.5 MPG which is prob high 18's. We shall see but I haven't had the DIC this high on a mix before.