The first GT4 in North America
06-13-2015 | 02:49 PM
#91
Rennlist Member
Joined: Oct 2008
Posts: 8,556
Likes: 1,389
All metal wheels dissipate heat. Its a metal body attached to another metal body. If one heats up, the other attached will experience heat transfer. The more surface area you have the more heat will be dissipated. Law of physics/thermodynamics.
06-13-2015 | 05:09 PM
#92
Burning Brakes
Joined: Feb 2015
Posts: 940
Likes: 5
From: Edmonton, AB
06-13-2015 | 08:02 PM
#93
Burning Brakes
Joined: Apr 2009
Posts: 867
Likes: 2
From: Tyler, Texas
Yes, all wheels will act as a heatsink, that is true. I think what fishing is driving at is that if the 410 mm PCCBs reduce downforce because they reduce airflow through the wheel spokes (being closer to the barrel of the wheel), then the 380 mm iron brakes will similarly reduce airflow if coupled with a smaller wheel. It is a consideration.
06-13-2015 | 08:16 PM
#94
Rennlist Member
Joined: Oct 2003
Posts: 3,728
Likes: 708
Brake discs dissipate heat mainly through convection and radiation. At high temperatures radiation becomes critical, because it grows as an exponentail function to the fourth power of temperature. If you're watching Le Mans now you'll see the brake discs glowing orange or yellow- that's radiation cooling, beaming huge amounts of heat energy out into the night. It's important that you don't block this and reflect that energy back towards the disc, as something like a classic Fuchs wheel will- the more open the better. Airflow is just as important, also less so for downforce as the wheel well is a high pressure area that needs to be vented efficiently- the reason the iron disks help with downforce
There is also a conduction path through the bell to the hub and wheel, but designers work to limit it to insure wheel bearing grease isn't cooked, etc, rather than increase it and use the wheel itself for cooling. Porsche is careful to spec low thermal conduction materials for the bell for this reason, and by the time you get to the wheel temperatures are far lower. Because the forth power function in particular is so sensitive to temperature nearly all cooling ends up being done by the disc itself. So the best wheels for both cooling and downforce are very open...
06-13-2015 | 08:29 PM
#95
Burning Brakes
Joined: Apr 2009
Posts: 867
Likes: 2
From: Tyler, Texas
Thanks! Interesting stuff.
The wheels will have near zero effect on temperature due to conduction and heat sink effect, but how they block air or radiation plays a very large role in brake temperatures.
Brake discs dissipate heat mainly through convection and radiation. At high temperatures radiation becomes critical, because it grows as an exponentail function to the fourth power of temperature. If you're watching Le Mans now you'll see the brake discs glowing orange or yellow- that's radiation cooling, beaming huge amounts of heat energy out into the night. It's important that you don't block this and reflect that energy back towards the disc, as something like a classic Fuchs wheel will- the more open the better. Airflow is just as important, also less so for downforce as the wheel well is a high pressure area that needs to be vented efficiently- the reason the iron disks help with downforce
There is also a conduction path through the bell to the hub and wheel, but designers work to limit it to insure wheel bearing grease isn't cooked, etc, rather than increase it and use the wheel itself for cooling. Porsche is careful to spec low thermal conduction materials for the bell for this reason, and by the time you get to the wheel temperatures are far lower. Because the forth power function in particular is so sensitive to temperature nearly all cooling ends up being done by the disc itself. So the best wheels for both cooling and downforce are very open...
Brake discs dissipate heat mainly through convection and radiation. At high temperatures radiation becomes critical, because it grows as an exponentail function to the fourth power of temperature. If you're watching Le Mans now you'll see the brake discs glowing orange or yellow- that's radiation cooling, beaming huge amounts of heat energy out into the night. It's important that you don't block this and reflect that energy back towards the disc, as something like a classic Fuchs wheel will- the more open the better. Airflow is just as important, also less so for downforce as the wheel well is a high pressure area that needs to be vented efficiently- the reason the iron disks help with downforce
There is also a conduction path through the bell to the hub and wheel, but designers work to limit it to insure wheel bearing grease isn't cooked, etc, rather than increase it and use the wheel itself for cooling. Porsche is careful to spec low thermal conduction materials for the bell for this reason, and by the time you get to the wheel temperatures are far lower. Because the forth power function in particular is so sensitive to temperature nearly all cooling ends up being done by the disc itself. So the best wheels for both cooling and downforce are very open...