posted January 26, 2004 07:01 PM
Brake rotor warping question... So.... a fellow I was talking to suggested to me that automotive brake rotors (I suppose this could apply to bikes as well) warped when they were:
... overheated... then the driver was to stop at, say a light for an extended period... he suggested that stopping at a light and holding the brakes on allowed the rotor to cool at different rates... ie: the area covered by the engaged brake callipers would cool differently because of the contact of the pads and the pressure placed on the rotor in that one specific area... he suggested that this was the cause of warping...
I had never thought about this but it seemed quite plausible to me...
is he correct?
____________ What business is it of yours where I'm from, Friendo?
posted January 26, 2004 07:47 PM
If you get your brakes smokin' hot ,then reach down and pinch the rotor between your thumb and index finger, the area where your fingerprints are cools much quicker than the rest of the rotor. I guess this could promote warping.
____________
uh oh
posted January 26, 2004 08:55 PM
well, your pads are gonna touch whether u have the brakes applied or not, so not sure that would make a difference. but i think the concept of different heating rates causing warping makes sense. someone mentioned jsut a while ago that they like to always creep forward a touch at lights to let the rotors cool more evenly.
Needs a life
Full throttle!
Posts: One MEEEEEELLION
posted January 27, 2004 02:25 AM
In 99.999% of normal driving, I can't see that making a difference. The amount of heat you put in a set of rotors is minimal. The only time you ever really get the rotors hot, and I mean really hot, is during panic stops, or if you had to use your brakes to slow the vehicle down a loooong downhill, like Snoqualamie or somesuch. The most typical cause of warpage is when the rotors have been resurfaced a couple times, and are within a rch of their service limits. The thinner rotor heats up more quickly.
That being said, stock brakes are typically shit.
Brake rotors are usually your basic gray crummy cast iron. Rotors for
production applications are almost always sand cast, and do have some
built in stresses from uneven cooling- the automakers really are
primarily focussed on cost, so the quality of these guys is pretty
marginal. They are usually overweight to compensate. They have sand
inclusions, bubbles, prosities, and they are usually cast in one piece
with the hub- which leads to some nasty stresses whrn the OD is
incandescent and the hub is cold. It also leads to cooked wheel
bearings, pronto. They almost always exibit quite a lot of core shift,
which leads not only to balance problems but also to premature warpage
(due to one working surface heating more quickly than the other). This
is worsened in brake designs where the pads are asymmetrical, like my
Mustang- the driven pad is smaller than the slave pad, so the heat
loads differ on the two faces of the rotor.
The aftermarket rotors available for racing applications (Coleman,
Brembo, and other vendors) are usually a better class of materials-
some of the ASTM high-temperature cast irons are the norm. The best of
these are usually vacuum degassed to eliminate porosities that can
lead to cracking. These are also designed to run on a separate hub
adapter (the hat), which eliminates one major source of stresses and
also cuts the heat transfer to the hub and wheel bearings.
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posted January 26, 2004 07:01 PM
posted January 26, 2004 07:47 PM
