I think I've seen or heard of tires being melted off the rims due to the heat from the brakes, so I'm certain that the wheels are removing a substantial amount of heat by conduction. The wheel usually has a fair amount of contact area with the hub part of the brake disc, so the heat is being drawn out there.
That being said....This IS ecomodder! Why the heck are we worried about over heated brakes?!?
It has been said, "If you have to use your brakes, You're Doing It Wrong." Really this whole conversation could get us BANNED from the site, lets hope the moderators go easy on us. I suppose we could talk about this "Hypothetically" as well, like, "Suppose I was to one day go down a very long steep hill and my clutch/transmission went out preventing me from engine braking, and I could only use my brakes...." Yeah, that's the ticket.
