Rotor rub complaints drove much of the redesign work behind the BR-R8170 disc brake caliper from Shimano. The previous generation R8070 calipers worked well enough, but tight clearances meant that even minor wheel flex during hard cornering or out-of-saddle climbing could cause pad contact and the distinctive scraping sound that makes every road cyclist cringe. Ultegra's R8100-series caliper addresses this with 10% wider pad clearance, giving the rotor more room to move without touching the pads. That extra space also makes initial setup and wheel changes less fiddly, since you're not fighting to center the caliper within millimeter tolerances.

Modulation sees real improvement in this generation. The initial braking point arrives faster than the R8070, meaning the pads contact the rotor earlier in the lever stroke, but the expanded control range between first contact and full lockup gives you more room to meter braking force. This matters when you're descending technical roads where you need to scrub speed precisely without grabbing too much brake and unsettling the bike. The two-piston design uses resin pistons rather than metal, which reduces heat transfer into the hydraulic fluid and keeps the brake feeling consistent through extended descents.

Shimano's One-Way bleeding system gets easier in the R8170 thanks to a redesigned fluid path through the caliper. A separate bleed port and valve screw simplify the process of pushing air bubbles out of the system, which mechanics will appreciate and home wrenchers will find more approachable. The system uses Shimano's mineral oil rather than DOT fluid, so it's less aggressive if it contacts paint or seals and doesn't require the annual fluid replacement that hygroscopic DOT fluids demand.... Read More