I guess ur right on that. It got me thinking as to how much stress it would be on the rotors while driving in rain. It heats up and then water splashes on it cooling it very fast. Its surprising that this sudden heating and cooling doesn't make the rotors brittle.
>
> > Had the front brake pads replaced yesterday. On returning in the evening,
> > decided to touch the rotors to determine how hot they were. Just came off a
> > highway 60 to 5mph, then another hundred yards at 30mph and stopped. Burnt
> > my finger, it was like a hot iron. Rotor wasn't red or discolored, but i was
> > surprised at being burnt.
> > I expected the highway driving to have cooled off the rotors, so the only
> > heat generated would be the braking done after that. Is this heat normal or
> > am i thinking wrong?
> >
> > Sume
> > 93 Grand Am V6, 120K miles
> >
> >
>
> I'd be inclined to think "normal".
>
> Keep in mind you're talking about converting the kinetic energy of a ton
> or more of vehicle moving at 30MPH into a couple pounds of hot metal
> that isn't moving. That's a *HUGE* amount of energy to be pouring into
> the (comparatively) tiny little wafers that are your brake rotors. >
> I'm sure that the highway driving cooled things off quite nicely. But
> the braking at the end (and you can't forget the braking involved in the
> "60 to 5" part of the operation - that pours the energy into 'em, too)
> had to hammer all of that energy into the rotors in just a few seconds. >
> You damn well better believe they're gonna get hot! I'd be absolutely
> pick-my-jaw-up-off-the-floor amazed if they *WEREN'T* hot enough to
> blister you after "just" a 30-to-0 stop, let alone a 60-to-5 slowdown
> just seconds (100 yards at 30 = what? MAYBE a whole 10 seconds worth of
> cool-down time from the 60-to-5 manuever?) prior to that.
>
> (Hmmm... pardon me while I "stream-of-conciousness" for a second or
> three... I just got a brain-tickle, and I can't be happy until I figure > it out)
> *IN THEORY*
> 30 MPH = 30 * 5280 = 158400 feet per hour
> 15840 FPH / 60 minutes in an hour = 2640 feet per minute
> 2640 FPM / 60 seconds in a minute = 44 feet per second
>
> 100 yards = 300 feet / 44(FPS) = 6.8 seconds of travel time.
> This assumes an (impossible) instantaneous transition from 5 to 30 at
> the start, a constant velocity over the entire distance, and an
> instantaneous (again, impossible according to the laws of physics as
> currently understood - Erm... Well, not quite *IMPOSSIBLE*, but you'd be
> a greasy red mess being sponged off the interior of the car at the end
> of it, rather than a living human asking why he got burned) 30-0
> transition at the end.
>
> *IN REALITY*
> I bet you were probably braking for at least 40-50 of those hundred
> yards, all the while pouring a boatload of energy into the "tea saucers"
> that are your rotors on top of the even bigger boatload of energy from
> the 60-5 transition that you just dumped into them seconds before. >
> Are you still surprised they got hot enough to scorch you? :)
>
> --
> Don Bruder - snipped-for-privacy@sonic.net Hate SPAM? See for some seriously great
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