How hot do brake rotors get?
 

I know in race cars under heavy braking conditions the rotor run cherry red. I am wondering how hot the front rotors on street driven C3's get under normal stop and go traffic conditions? Anyone done any research on this? What I am planning on doing is painting the inner rotor (where the wheel bolts to the rotor) to keep the rust at bay. I am doing my front-end rebuild now and noticed my rotors have a lot of surface rust on them. I know I will probably be the only one to ever see them (except for the tire guy) but I hate rust. Is there any special paint I should use or will any do??
Thanks
John

Re: How hot do brake rotors get? (theandies)
 

Hey John,
I painted the rear rotors along with everything else POR15 black with their Metal Mask top coat. They came out ok but it was a lot of time and prep along with $$$- A simple spray can would work just as well. The PB was too tight when I first drove the car and it heated the rotors pretty good. The paint didn't peel but it does chip easier then the swap meet guys say when selling it.
Gary


[Modified by gtr1999, 11:27 PM 7/9/2002]

Re: How hot do brake rotors get? (theandies)
 

i did a technical project for my last year of engineering on brake rotor design. i learned that that calculating rotor stresses is easy, but calculating thermal cycles is very very difficult. geometrey, convection coefficents, conduction rates, forced vs free convection, specific heats, and transient thermal load inputs all have to be considered.

my application was a 750 lb open-wheeled racecar, with alumimum rotors, anodized. we measured temps after some hard autocross testing, and got 280-300 degF. 350 was the design limit.

for a 'heavy' C3, will grey cast iron rotors, braking from highway speed, i would estimate ~400 degF. stop and go city driving? ~200-300 degF

any paint from VHT should work.


http://members.shaw.ca/cam.grant/fsae/images/16.jpg

http://members.shaw.ca/cam.grant/fsae/images/17.jpg

http://members.shaw.ca/cam.grant/fsae/images/32.jpg


[Modified by Turbo-Jet, 2:07 AM 7/10/2002]


[Modified by Turbo-Jet, 2:08 AM 7/10/2002]

Re: How hot do brake rotors get? (Turbo-Jet)
 

Turbo:
That's a neat study. As you know stopping an automobile requires a lot of work. Energy is being dissipated in a small area. It's a fundamental application of the first law of thermodynamics. Or in other words heat is a by product of work. Congratulations on your completion of enginnering school. I'm an old EE myself. As a matter of fact I'm working now and getting hot! :lol: :lol:

Re: How hot do brake rotors get? (Turbo-Jet)
 

Hey Turbo - Thanks for the info....very Cool :cool: :cool:
I'll play it safe and find a paint that will withstand anything 500 degrees and over just to give me a little fudge factor.
John

Re: How hot do brake rotors get? (theandies)
 

Speaking strictly about racing rotors, the one you see glowing are carbon rotors. Steel or cast rotors do not hold up as well and are pretty much junk if they get that hot. On a 69 428 road racing Mustang I helped out on, we ran 12.5 vented and drilled NASCAR rotors and had to replace them after 10-15 hours of use. The trick is to get good balance between the fronts and rears, and supply LOTS of ventilation to all of them. We ran two 4" flex hoses to each front brake and one to each rear disc with 962 Porsche style fans on the front wheels.

Hans

Re: How hot do brake rotors get? (theandies)
 

My rotors have been painted for years with normal black gloss paint. Both the center section and the vanes and nothing has discolored. I have done a few panic stops from 100 mph and filled the car with smoke but no problems with ordinary paint.
My calipers are gold anodized, well not really anodized but gold phosphate coated then overpainted with gold and they too are fine.

Re: How hot do brake rotors get? (norvalwilhelm)
 

Thanks Norval,
I have some spray bombs in the garage. I think I'll use them now that you have been the guinea pig. I was just concerned about FIRE :eek: :mad :eek: if you know what I mean. I don't care if it discolors but I just want to keep the nasty rust down some.
Thanks
John

Re: How hot do brake rotors get? (theandies)
 

It's not just race cars that have glowing rotors. In Vermont there is a hillclimb up Mount Equinox every year. People go to the restaraunt at the top afterwards. At night time at the base you can see the rotors glow on people's cars who never heard of using low gear down the mountain. One lady stopped at the bottom long enough for the heat to soak her bearings and the grease caught fire! Joe