Flat Mount MTB

Flat Mount MTB

What’s old is new again. Circa 1997. The Hayes 22mm caliper mount. Believe it or not, this is what changed mountain bike braking forever and truly brought disc brakes to every day mountain bikes. Back in ’97 or ’98, I bought a bike with these brakes on it. I was the first in my crew to do so. Very shortly after, we did a big rain ride. I got to the bottom of a long and rowdy trail, well ahead of everyone else, feeling good and on a solid bike. Then, after a while, they showed up with their v-brakes; hands sore, brake pads roached and ground down, They were suddenly slow. Rim brakes were #over.

Less than a week ago, flat mount 160/180 specs have been ‘published’ though that doesn’t mean that I or anyone I know will be using these numbers. Assuming that SRAM and Shimano get on board, then it’s settled. Until then, it’s not. Most importantly, they wont, it’s wrong.

This seems to have been a marketing stunt published by Mark Landsaat of the new Noble Bikes effort. His history is largely with Raleigh bikes, a company that has made many mistakes with brake adoption recently. Supposedly, Magura and Tektro have looked at this but I’m still looking for some kind of confirmation on this.


Adding more confusion to this, a Whyte S-150s that I have in my basement has 160 flat mount rear caliper mount at a 19.25mm face offset. This doesn’t agree with Landsaat’s figures or what I’ve reverse engineered from SRAM. I spoke with the designer for the Whyte system and know what they did for their mount and that it is considered 100% proprietary dimentionally.

The big mistake that many people are making when looking at this issue is using the adapters to 160mm to base their numbers on. You should not be using adapters to make this measurement. Adapters are problem solvers, not standards. A setup may “work” but not be correct with an adapter, and this is very often true. Flat mount adapters are designed for overlapping screws to have space, to look good, keep clearances, and to basically function. They most certainly are not a valid reference.

I had done my own calculations with some SRAM parts I had on hand a few months ago for another project and had calculated 21.84mm offset plane and 44.62mm distance for 160mm rotors. It’s hard to imagine what makes for such a discrepancy. I take the parts and bikes that I design very seriously and have no intention of using numbers pulled out of thin air.

The specification is simply, wrong. The numbers that Landsaat posted aren’t correct, even remotely, if any investigation into them is done. Below, I show a proper calculation for SRAM, Shimano and SR/SH flat mount calipers. The working angles were arrived at via reverse engineering and the exact engineering angles may differ slightly, and other calipers may have differing pad angles. Still, this is a consistent and correct construction. It may change slightly as time goes by and more details get figured out, keep cautious!


Here is the Shimano caliper modeled. (5/4/18, I’m starting to see info that the Shimano caliper is at a 30.5 angle with a 1.25mm offset above the axle in 140mm configuration. More info on this as the days progress)


Mark at Paragon Machine Works has gone a similar route to others and reverse engineered from the rear 160 adapter for 18.77mm offset and 46.36 first hole. This can be seen on parts like the PMW B4041 Slider mount. As a note, many of Mark’s earlier flat mount parts use the 2mm Shimano slot while newer parts use the 3mm SRAM slot.

Jeff at Sputnik Tool is already at work making tools for frambuilders to go with FM160 and FM180!

The real problem now is quality brake pads and calipers for use with this mount. Flat land XC riders are fine with what’s available. Gravel/road folks don’t need anything over 140mm rotors anyway. Where’s the beef?

So far, the only real caliper capable of being used in duties over XC is the Hope RX4. SR (SRAM) and SH (Shimano) designated the system that they are designed for. What’s cool here is that they are making a specific front FM caliper to do away with adapters. Cool and clean.

With SRAM, Level levers are interchangeable with the drop bar levers so that should be proper to start but the Guide lever should be tested.