I hadn't even thought about the rotor size. My new bike has a 140mm rotor in front, and I start my day with a tasty descent. The stopping power has been plenty good with the 140's but now I'm wondering if I should put something bigger on there just for heat management. I'm not a small guy, and my morning descent winds up with me going about 35 mph approaching a pretty busy cross street, so I've got a lot of energy to disperse in a short time with rather nasty consequences in the event of brake failure.