At the front, the calliper is fixed to a thin adapter which is bolted to the fork.ĭepending on frame design and disc rotor size, post mount often needs a large and ugly adapter to provide the correct spacing over the rotor.

Where post mount callipers are bolted from above directly into the frame and fork, flat mount callipers sit flush with the frame and fork and the bolts are threaded in from below and directly into the calliper, pulling it down onto the frame. The key difference is in the way the calliper is mounted to the frame. The actual calliper mechanism is identical and there are no changes to the way the hose connects and the brake pads are installed. There’s no doubt flat mount disc callipers are smaller, better looking and lighter than the bulkier post mount callipers. “ smaller and more compact interface with the frame/fork for improved integration, reduced weight and better tool access for easier adjustment,” Shimano told. The vast majority of new disc brake road bikes are flat mount. It’s an open standard that has been quickly adopted by other disc brake manufacturers. To try and improve the appearance of discs on road bikes, Shimano introduced its flat mount system. 2 Disc brake rub can be an issueĮarly disc-equipped bikes borrowed the 74mm post mount standard from mountain bikes, where the brake calliper is simply bolted directly onto the frame or fork and adapters are used to accommodate different rotor sizes. The weight difference isn't huge but it can often be around a pound over the whole bike when everything is taken into account.

Read Everything You Need To Know About Disc Brakes The thru axles that are used with many disc systems are heavier than quick release skewers. Manufacturers often try to minimise the difference but don't forget that disc brake hubs are heavier too, and disc brake wheels are often built up with more spokes of a wider gauge, although the lack of a brake track means that disc-specific rims are generally lighter. Levers, brake callipers, hoses, fluid and rotors weigh more than an equivalent rim brake setup. The all-up weight of a disc brake bike is higher than that of a rim brake bike. Here are some of the issues that we've experienced and heard about. Disc brakes have become an increasingly important part of the road bike world over the past few years, but while the benefits of disc brakes are well documented, they bring with them challenges and problems too.

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