Karate Monkey
Well-Known Member
I agree that the differences will be minimal hence my initial statement that two piece rotors don't resist warping(even if the center is a more conductive material whatever interface is between them will likely negate any additional conductivity of the material). Even the floating ones are mostly targeting the caliper/rotor misalignment typically caused by pistons not being truly even in a caliper as it advances the pads(these are even worse for heat transfer since there is an air gap between the spider and the brake track to allow it to float) There is alot of math going on to try and determine that these different designs are better at ______(fill in the blank) but the overall improvement is going to be minimal and likely unnoticed by the rider (definitely in NJ where long downhills are kind of uncommon)
Correct. Bicycle two-piece rotors are almost entirely about weight savings. There's no heat benefit/warping protection in reality from the spiders (didn't think I was saying there was?). Just so we're clear that we're talking about the same thing:
Floating Rotor
Two-piece
They're constructed differently (at least in theory). The brake track on the floating rotor does not--as expected--contact the spider directly. It touches the bearings, which allow it to expand--again--theoretically. The bottom brake track is fixed directly to the spider. The extended black bit hanging off the brake track is the aluminum core that is stamped into shape/painted with heat-dissipating treatment. The braking surface is literally a stainless sandwich around the aluminum core; the spider is a separate part altogether.
Warp may not be the term that would be used in the automotive world, but again, warping in the sense of a totally FUBAR'ed rotor doesn't really happen on bicycles from heat...the pads lose any ability to apply friction before that would happen (okay, maybe the Hydraulic Press channel?). Rotors definitely get wiggly [note: maybe this term is less offensive?] as they heat+cool. Fractions of a millimeter, yes, but that's really all the clearance that brake calipers have on bicycles; it makes zero difference as far as stopping/going ability, until it cools back to normal operating temps. I've seen rotors that radiated a purple HAZ ~1.5cm down the spokes (one-piece stamped rotors) that were still dead straight.
None of it matters for NJ, as you noted. You could probably stop the bike with an unusually stiff piece of cardboard.