How to Fit 180mm Brake Rotors on Flat-Mount Frames/Forks

compose Josh Meissner
time Nov 17, 2022
comment 37

Like it or not, flat-mount disc brakes are here to stay. Originally a road standard designed to integrate disc brakes on slender carbon frames and forks, the smaller calipers have become the only type included in modern hydraulic drop-bar groupsets from the big component manufacturers, with post-mount brakes relegated to flat-bar MTB groupsets. Accordingly, frame designers have had to follow suit, with many drop-bar mountain bike framesets inheriting the flat-mount standard.

This trend hasn’t delighted everyone. The sleeker flat-mount package mostly tops out at 160mm rotor diameter, which puts a hard cap on the heat flux available for cooling a glowing rotor during a long descent. Pad and disc longevity suffer accordingly, and the effects are magnified the heavier the rider and bike.

A few pragmatic brands have identified flat mount’s inadequacy for loaded off-road riding and designed their frames and forks for 160/180mm rotors, notably the Tumbleweed Stargazer, Salsa Cutthroat V2 fork, and new Seido MGV fork. By and large, though, riders looking to upgrade the braking on their modern drop-bar bike are limited by a standard inherited from the road and performance gravel space.

Now, there are at least two aftermarket adapters that allow for 180mm rotors on standard flat-mount frames and forks. These adapters take the form of a mounting plate that’s either stacked with the existing one or replaces it entirely. This moves the caliper out an additional 10mm to wrap around the larger rotor. These adapters exist outside of official manufacturer specifications, so not every frame is compatible, running them will most likely void your frame/fork warranty, and you’re proceeding entirely at your own risk. Still, we think they are well worth highlighting for bikepackers and heavier riders looking to beef up their braking systems.

Peak Torque Big Brake Converter

Alex, a mechanical engineer who’s reportedly worked on rotary machinery for over a decade and goes by the handle of Peak Torque on his independent bike engineering YouTube channel, developed the Big Brake Converter (front and rear specific) for running 180mm disc on forks and frames that follow the 140/160mm Shimano flat mount standard. He stresses that the primary purpose of the larger disc is for better cooling and thus lower temperatures, which means reduced fading and longer life of the pad and rotor.

He provides detailed fitting notes and tips for mounting the adapter securely. While the slightly increased braking forces should be well within the safety factor of a frameset, you’re completely on your own when it comes to damage or injury. The converters are available in his webshop, which is periodically restocked. Dig his YouTube video below for the engineering considerations that gave rise to the useful design:

You can head over to Peak Torque’s website to find additional details about the 180mm adapters for frames and forks. They’re priced at $41 and $50, respectively.

Discord 180mm Flat Mount Fork Adapter

Keen eyes will have spied a flash of silver on the stunning fork in Joe Cruz’s review of Tanglefoot’s incredibly capable Moonshiner ATB. Vermont-based Analog Cycles developed the Discord 180mm Flat Mount Disc Brake Fork Adapter to bring the braking on their drop-bar all-rounder up to par with its singletrack prowess. The two-piece design is made in the US, comes with stainless hardware, and is available in black or silver anodizing. Analog Cycles advises to check with your frameset’s manufacturer whether it can handle the increased braking loads.

Find more information over at AnalogCycles.com. Their adapter retails for $60 in silver or black.

Additionally, a reader notified us that component manufacturer XLC makes the BR-X106 and BR-X107 adapters, which achieve a similar purpose as the ones mentioned in this post and, while hard to find, look to be an inexpensive alternative for folks in Europe.

What’s your preferred brake system for bikepacking? Let us know what you think about the proliferation of flat-mount brakes in the conversation section below.