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Old 04-17-2007, 10:38 AM   #1
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Wheel aerodynamics and brake cooling

I'm wondering whether doing aero mods around the wheels could cause the brakes to overheat.

I was at the tire shop yesterday getting my summer tires put on and I started asking about skinnier tires. I have 14" wheels, and I was talking to the guy about various tire options. I mentioned that I could get some 13" wheels and he said that you have to be careful because the smaller wheels can shroud the brake disc and prevent enough air from getting in and cooling the brakes. That makes me think that removing a significant amount of air flow from around the wheels could lead to brake overheating problems.

I guess if the vehicle were also significantly lightened and you had drilled out discs or something like that then the brakes could work okay with less air flow.

Just wondering if anyone has thought of or encountered this issue.
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Old 04-17-2007, 10:48 AM   #2
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It's not like we use our brakes when we can help it.
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Old 04-17-2007, 11:11 AM   #3
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Here's a thread on it.
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Old 04-17-2007, 11:57 AM   #4
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I read some of the thread, Thanks. Of course, an FE conscious driver would avoid using the brakes hard, however, I've noticed that I use the brakes a little more now that I've changed my driving style and do a lot more coasting. Still, I go pretty easy on the brakes since I'm always trying to conserve momentum. But I guess it could really be an issue going down a long mountain pass if you didn't want to use the engine to check your speed, or if you wanted to engine-off coast down. Then it might be something to consider if you had done some signifiicant wheel aero mods.
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Old 04-17-2007, 11:58 AM   #5
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Volvo driver here. Safety fiend.

I'd avoid doing anything that would interfere with cooling the brakes. The one or two times when you REALLY need them you want them to work 100%. The rest of the time you won't use them to their full capacity but you still don't want to abuse them - you want them there for you when needed.

When you demand 100% from them they will heat up seriously. The built in cooling will be up to the job but compromised cooling probably won't What happens is the brake fluid changes (vaporizes?) when it gets hot enough. After that it no longer functions as designed.

As tempting as moon hubcaps are, I'm staying with slotted ones. I'm considering fender skirts for my rear wheels but at least they'd still be partially open if I add skirts. And the heavy brake action is in the front wheels.

"I hit the brakes as hard as I could but... " doesn' really cut it after you hit something. You might be the only one who knows why they failed - but you'd know.
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Old 04-17-2007, 12:06 PM   #6
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Quote:
Originally Posted by brucepick View Post
Volvo driver here. Safety fiend.

I'd avoid doing anything that would interfere with cooling the brakes. The one or two times when you REALLY need them you want them to work 100%. The rest of the time you won't use them to their full capacity but you still don't want to abuse them - you want them there for you when needed.
Hrmm... When you really need your brakes 100%, it's an emergency situation... Brake and steer as fast as you can... All of this happening very quickly - very short period of time. The reason I'm saying is - the time involved in an emergency stop is so short that the amount of heat loss due to cooling is very low. Now if you needed this two times in a row within a pretty short time - that could be a problem (although why would we be lead footing :P).

As for brake fluid and boiling.... That could be a problem in an emergency -- but it would be a problem regardless if you didn't keep up with maintenance and flush your brake fluid regularly like a good owner should :P New fluid boils above 400F -- very old fluid may start boiling around 250 (dependent on water content) :/

Just playing devil's advocate Then again, I do live in Florida... More heat, but very little in the way of mountains :P
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Old 04-17-2007, 04:04 PM   #7
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its not like on a sports car were not using them to the exstreem level they are.
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Old 04-17-2007, 06:35 PM   #8
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I have moon hubcaps on all foru wheels, wheel well skirts over all four wheels, and also exhaust my hot radiator air out through my front wheel wells, so mine should be a "worst case" situation. I have to do a fair amount of braking while coming down the mountain from NC and I have never had any problems with brake fade.
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