How hot do wheels get?
08-03-2003, 05:55 PM
#1
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How hot do wheels get?
OK, I'm wondering how hot a wheel gets on the track. Of course, the best way to do this is to actually measure, but I don't know quite how to go about taking the temperature of a wheel. So, I figure I'll try a theoretical approach:
PV=nRT
Let's assume that the volume (V) of air inside a tire remains constant once the tire is filled. Let's also assume that the number of gas molecules (n) inside the tire remains constant. If these assumptions are valid, then the pressure (P) of air inside the tire is directly proportional to the temperature (T) and only the temperature.
Let's say the pressure before a run on the track is 35 psi at 25C (298K). Here's where I need a little help. What is a reasonable pressure at the end of a run? Is 42 psi reasonable???
Let's say 42 psi. That means the pressure has gone up 20%. If my assumptions above are correct, then the temperature of the air inside the tire has also increased by 20%. This would mean the temp is 358K.
358K=85C=185F
So, 185F for the temperature of the air inside the tires. Empirically, I have determined that the wheel is hotter than the tire. After a run on the track I touched the sidewall of a tire. It was hot, but I could hold my finger on the sidewall without burning it. When I touched the actual wheel, I couldn't hold it there for more than a second or two without serious discomfort.
So, I'm figuring the wheel heats up to 200F or higher on the track.
Does anyone care to add anything to this? OK, so I probably have better things to do . . .
For anyone who has seen my thread on baking wheels in the oven, this is related. As a matter of fact, I have a wheel in the oven right now baking at 200F. I have already done two others, and the paint still looks fine. Perhaps I'll apply wax tomorrow.
Cheers,
Mark
PV=nRT
Let's assume that the volume (V) of air inside a tire remains constant once the tire is filled. Let's also assume that the number of gas molecules (n) inside the tire remains constant. If these assumptions are valid, then the pressure (P) of air inside the tire is directly proportional to the temperature (T) and only the temperature.
Let's say the pressure before a run on the track is 35 psi at 25C (298K). Here's where I need a little help. What is a reasonable pressure at the end of a run? Is 42 psi reasonable???
Let's say 42 psi. That means the pressure has gone up 20%. If my assumptions above are correct, then the temperature of the air inside the tire has also increased by 20%. This would mean the temp is 358K.
358K=85C=185F
So, 185F for the temperature of the air inside the tires. Empirically, I have determined that the wheel is hotter than the tire. After a run on the track I touched the sidewall of a tire. It was hot, but I could hold my finger on the sidewall without burning it. When I touched the actual wheel, I couldn't hold it there for more than a second or two without serious discomfort.
So, I'm figuring the wheel heats up to 200F or higher on the track.
Does anyone care to add anything to this? OK, so I probably have better things to do . . .
For anyone who has seen my thread on baking wheels in the oven, this is related. As a matter of fact, I have a wheel in the oven right now baking at 200F. I have already done two others, and the paint still looks fine. Perhaps I'll apply wax tomorrow.
Cheers,
Mark
08-03-2003, 06:02 PM
#2
The rubber could indeed be hotter than the metal, but since metal conducts heat better it won't feel that way. Grab a plastic tray and a metal tray out of a freezer-the metal will feel much colder.
The easiest way would be to just get some type of temperature gauge.
The easiest way would be to just get some type of temperature gauge.
08-03-2003, 06:15 PM
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Oh, I have no doubt where most of the heat is coming from--the brakes. I imagine some of the heat that warms the air in the tires comes from the friction between road and tire, but I'm assuming that most of it is coming from the brakes through the wheels. I assume all of the heat in the wheel is coming from the brakes.
08-03-2003, 06:24 PM
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The road friction/pressure change will contribute slightly, but not a hell of a lot. When on full stop, a brake disc could reach like 600-700C, thats over 7 times the tyre temp!
