If you're running a >30mph ebike, you probably want something larger than 160mm rotors and something heavier duty than XC disc brakes. I'd suggest some downhill

If you're running a >30mph ebike, you probably want something larger than 160mm rotors and something heavier duty than XC disc brakes. I'd suggest some downhill gear, including DH forks, headset, bars, cranks, etc. Shimano has the Saint line: http://bike.shimano.com/content/sac-bike/en/home/components11/mountain/saint1/br-m820.html http://bike.shimano.com/content/sac-bike/en/home/components1... Hope makes some nice DH brakes: http://www.hopetech.com/product/tech-3-v4/ http://www.hopetech.com/product/tech-3-v4/ Avid has the Code: https://dirtmountainbike.com/bike-reviews/brakes-gears/avid-code-brakes.html https://dirtmountainbike.com/bike-reviews/brakes-gears/avid-... And other manufacturers also make calipers with >=4-piston calipers. Again for rotor size, 160mm is typically standard for XC, road bikes run 140mm usually, some "all mountain" bikes have 180mm fronts, and 200mm is typically seen only on DH/4x/trials/dirt jump bikes but likely what you want for a fast ebike. All that said, competition-level road bikes generally hold up fine at speeds up to 60mph (and the riders hit those speeds going down hills) and their brakes work fine. You obviously don't just mash them, and the rim surface they're clenching matters a lot, as do the pads, but the tech works well and has worked for the past 100 years. Weight distribution and even application of both brakes help a lot.