160mm -> 180mm brake rotor upgrade, heat issues

Cameron Newland

Well-Known Member
So I recently upgraded my front disc brake rotor from 160mm to 180mm, and I felt a difference in braking immediately. Braking force was smoother and more powerful, and running 160mm rotors front and rear definitely isn't confidence-inspiring as I weigh about 190 lbs (not to mention the extra weight from the motor and battery).

Anyways, on my first medium-distance ride with the new brakes, there were some relatively steep descents, and I definitely felt a some brake fade on the front brake after descending for a few blocks. This surprised me, as I figured that the larger rotors would be better at shedding heat than the smaller rotors were, due largely to their increased surface area. I could also smell my brake pads (or rotors) when I got to a stop sign. They weren't visibly smoking, but the smell was really noticeable, which scared me. Luckily, the rest of the ride was much more level, so at that point, I quit worrying about my brakes for the moment.

After the ride, I looked at the brake rotors, and the area of the rotor just inside the area where the pads touch the rotors had been visibly discolored. It's now a mix of purple and blue, and I'm certain that the discoloration is a result of extreme heat (300F+). I imagine that the area directly under the pads also got discolored, but that discoloration may have been wiped away from the pad friction. I also realized that these 180mm rotors are slotted instead of cross-drilled, so there is a lot more surface area for the brake pads to grab onto, but a lot less area to dissipate heat.

Did I make a rookie mistake by buying 180mm slotted rotors instead of 180mm cross-drilled rotors? Is this a common mistake? Could I fix this by either getting 180mm cross-drilled rotors, or by installing brake calipers that are meant to deal with a lot of heat in the pads/caliper by dissipating the heat via the calipers? I do have an extra set of Magura MT5e 4-piston hydraulic disc brakes that I could put on this bike, and I imagine those would work just fine with these new slotted disc brake rotors.