Sumart FR3H Floating Disc Brake Rotor, 6-Bolt

Built for: mountain bikes. Sumart pitches the FR3H at riders who are "racing downhill or navigating tricky trails." Sumart says the floating design allows for better rotor expansion and contraction, with reduced heat buildup.

Fits: a 6-bolt hub, in 160, 180, 203, 220 and 254 mm. The braking band is 1.8 mm thick (2.25 mm on the 254 mm), so check that your brake takes a 1.8 mm rotor. Not for SRAM Maven or Lewis 4-piston brakes.

How to pick a size (our advice): match what is on your bike now unless you are deliberately going bigger. 160 and 180 mm are the usual sizes on cross-country and trail bikes; 203 and 220 mm are what enduro, downhill and e-mountain bikes run, where more rotor means more braking power and more room to shed heat. Going up a size needs a caliper adapter, and your fork and frame have a maximum rotor size, so check it with the bike maker first. The 254 mm is bigger than most bicycle forks and frames are made for; only fit it if yours are rated for it.

A two-piece floating rotor: a 7075 alloy carrier with a 410 stainless steel braking band, in black. Sumart says it is designed to reduce noise and drag. One rotor and six fixing bolts in the box, enough for one wheel. Ships from a US warehouse.

Why we carry it: a floating rotor for riders who brake hard and long, from the maker of the pads, bleed blocks and tools we already carry.

Installing it: Sumart stresses getting the torque right on every bolt, so use a torque wrench, and bed in a new rotor before your normal ride. Riding a commuter e-bike with a 180 mm rotor and a 2-piston brake? The Tektro TR-52 we keep in Sacramento is the simpler, less expensive match.

Care guide: cleaning, contamination and bed-in.