nitrogen in tires error!

In your article from 16-Feb-2007 you state that “As for moisture, changes in humidity affect tire performance two ways. First, the density of humid air fluctuates more with temperature than that of dry air, so removing humidity can keep your tire pressure more consistent, especially when the temperature climbs over 100 degrees Fahrenheit. That may be a legitimate concern in Formula One racing, but it’s not much of an issue if you’re just tooling around town.”

Can you tell me what temperature a tire is when it is 90 degrees Fahrenheit… if the tire is being driven on a black top highway at 65mph? I am willing to bet that the friction alone will get the tire hotter than 100… much less adding in the blacktop or a possible under-inflated tire.
P.S. The green caps are sexy!

Hi PHYCOputz

It’s customary to include a link to the article.

No biggie,welcome to the Dope,hope you stick around.
Hopefully someone with a real answer will be by soon.

Forgot to include the heat produced by the braking system of the automobile in question!

Hi PSYCHOputz Welcome to the boards.
In reverse order, unless you are racing heat transfer from the brakes will be minimal to non-existent.
Next when driving down the road, the tires will be cooled by the air passing over them as they rotate. While it is true the asphalt will be above 100F when the air is in the nineties, not that much of the tire will be in contact with the road surface at any one time, and when you are driving at freeway speeds that contact does not last long as the tire is rotating.
[off the cuff back of the envelope type calculation mode] The tires on my car are just under 2 meters in circumference (1960-1980mm somewhere in there) so 2 meters is close. To make the math easy assume a car speed of 100 KPH so the tire revolves 50,000 times per hour or 833.33 RPM [/OTCBOEC] The contact patch is changing pretty damn fast and doesn’t have much time for heat transfer.
Tell you what, I am leaving on a trip tomorrow where I will be driving extended periods at high speed. I will take my infrared pyrometer with me, and I will take some measurements. I will report back on Monday.

Look forward to the results. Be sure to measure the rim temperatures and add that to the calculation, especially when coming off the highway.

Wish I could edit my posts… Remember we are talking internal “air” teperature not the temperature of the tire itself.

If you join the board as a full member, you can edit your own posts (only) for up to 5 minutes after posting them.

Off the top of my head, I can’t think of any reason that the air in the tire would not be the same temp as the temp of the rubber.
Also there is no easy way to do this.

I agree. It should effectively reach equilibrium fairly quickly.

In this post in an earlier thread, Joe Fricken Friday says:

What about the heat generated by flexing, which can be considerable?

I imagine that’s the primary cause of the 10% temperature increase. After all, what other energy source would cause a temperature increase? You’ve got: 1. conduction from the road (if the asphalt is hotter than the air), 2. static friction between the tire and the road (if you seperate that from the overall tire flex), 3. brake friction, 4. wheel bearing friction, and 5. tire flex. I would think the last one would be the only non-negligible source of heat into the tire.

#4 is a non starter. If you wheel bearing are running anything above room temp you have serious problems. Wheel bearing are not a source of heat. At least they had better not be.
#3 is almost a non starter. Unless you are racing, you brakes never get that hot. Sure the rotors get warm toasty even. But there is not a good conduction path from the rotor surface to the air in the tire. To heat the air in the tire, first you have to get the rotor hot, then the hub hot, then transfer heat to the wheel via the lugs and mounting surface, heat the entire wheel, and finally you will get the air in the tire heated.
While all of this is going on, you have air blowing all over every part of this, cooling it back off.

I agree that with an aluminum wheel the heat transfer will be lower, but in the case of a steel wheel under a hubcap/wheel cover, the transfer will be far greater. Even enough to heat the tire.

I work in the auto industry and have been measure tire, rim, and ambient temps all day. I will post them when I get home from work.

Alrighty then, today’s ambient temperatures ranged from 80 to 87 degrees F. Using an infrared thermometer at a distance of 1 inch, I measured the driver’s front tires and rims from random cars throughout the day. All of the rim temperatures were measure in the drop center area (rim area closest to the tire’s tread, not to be confused with the bead area) on the exterior. All of the tire temperatures were taken on the outer sidewall at the 12 o’clock position.

Results… tire temperatures ranged from 88.2 to 140.1 degrees F. Rim temps from 87.3 to 108.7. The rim and tire temps seem to have very little to do with one another. One vehicle had a tire temp of 114.2 and a rim temp of 102.0, whereas another had a tire temp of 102.1 and a rim temp of 103.2.

The most pleasant result is when I got home and found my other car parked in the sun. It hasn’t been driven in 2 days. With the ambient at 87, the tire was 142.3 and the rim at 108.7.

I realize that my automotive infrared thermometer (make - ES, model - EST-65) may not be lab accurate, but it’s got to be pretty close.

Not to confuse anyone, the rims were not measure “IN” the drop, but next to it.

OK, I’m back.
On Friday after two hour run on the freeway, followed by a 5 mile trip up a secondary high way and about 3/4 of a mile I parked the car.
Measurements were taken within 1 minute of stopping.
Air: 91F
Tread: 118F
Rim (near bead):112F
Rim (1/2 way to center) 109F
Rim (near center cap): 106F
I did not get the temp of the pavement.

coming home:
2 hour run of the freeway, followed by hard braking at off ramp, and two miles on surface streets to home.
Air: 86F
Thread: 112F
Rim (1/2 way between center and bead) 106F
Front rotors: 146F
Pavement: 96F (pavement in shade for about 1 hour prior to measurement)

My conclusions:
The tire will run above ambient temps, but not alarmingly so.
Brakes are not a source of heat to the air in the tire under normal conditions. This would not apply to racing conditions.
Results might be different if reading were taken as soon as the car stopped. (not driven on city streets / secondary highways.

I had a feeling your numbers would come be close to mine.

I have actually heard that the tires can get pretty warm (above 100F) in winter as well, pending dry pavement. Will have to take some more measurements in a few months.