Calliper rim brakes are very good, road disc brakes are gaining in popularity, so is there room for direct-mount brakes?

Every bike manufacturer worth its salt has launched an ‘aero’ road bike in the last few years. Typically that means a frame with svelte, kammtailed tubes, a rear wheel cutout, internal cabling, and ‘direct-mount’ or ‘post-mount’ brakes that are attached directly to either side of the fork or stay via two posts. This last ingredient certainly looks aesthetically pleasing, but do direct-mount brakes actually provide any practical benefit?

Specialized’s David Alexander says they require extra considerations by frame designers: “The design criteria for post-mount brakes, needing the two posts on there, does change the style of how you would create a frame. And of course you have to consider where you’d want to stick them on the frame.

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“For the rear brake it would sometimes be pretty difficult to put them on the seatstays, which is why you find so many post-mounted rear brakes under the chainstays,” he says.

“On a bike that doesn’t need to do a lot of braking that position under the chainstays is OK. But when there have been investigations into the most performance-orientated position of brakes on a frame, it’s been found that underneath the chainstays is pretty much the worst place for a rear brake.

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He adds: “Fitting a rear brake underneath the chainstays has the effect of the wheel trying to rip the rear brake off the mounts. At least if you put the brakes at the top of the seatstays, the wheel is only trying to push the brakes into the seatstays, which is impossible.”

Aero possibility


EE Cycleworks direct mount brake with aerodynamic cover

What about aero benefit? “That area around the bottom bracket has been looked at by our team in the wind tunnel and it’s actually not as dirty an area for air flow as first thought,” Alexander says.

“The chainrings and cranks are moving, but they’re either side of the chainstays. So it might be beneficial to have a really clean area down there, but that’s disrupted by putting a brake there.

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“The only way post-mount brakes could really have an aero advantage would be if they were 100 per cent integrated and fitted in line with your fork blades or stays. You’d need to completely hide them and almost make them part of the frame.”

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Some bike makers have taken almost a proprietary route to post-mount brakes, such as Fuji, which lobbied Shimano to make seatstay-positioned direct-mount brakes for its new Transonic aero bike.

“I know some of the people at Shimano — I used to race with one of their product guys — and he agreed with me about this, so Shimano started the development of a seatstay direct-mount brake,” Steven Fairchild, Fuji Bikes global product manager says.

Stronger and stiffer

b'twin ultra 720 af direct mount brakes shimano ultegra

These direct-mount brakes are even better than the standard Ultegra offering

“What they did was to take the front direct-mount brake, turn it around, put a stronger spring in it, and then put it through their testing and stress analysis.

“Looking at the way these brakes mount directly to the frame removes redundant material on the brake and it’s a more efficient system. It’s stiffer and since it fits closer to the frame it’s more aerodynamic. Shimano hasn’t come out with any performance figures, but I’d say they must be stronger and stiffer than regular calliper brakes.”

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However, Fairchild isn’t convinced by chainstay-mounted brake systems. “I don’t think that’s a very good place to mount a brake on a road bike. It does make the bike look cleaner, but I’m a form over function guy, and from a functional standpoint the chainstay-mounted brake just doesn’t make a lot of sense.”

Our take

Pinarello disc Team Sky

Disc brakes are stealing the show when it comes to new innovations

Direct-mount brakes might be a great idea, but they’re coming at a time when a lot of their claimed benefits will be trumped by disc brakes. To make the most of direct-mount brakes, manufacturers have to radically alter frame designs. Fuji has done this successfully with the Transonic.

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However, we think many brands that fit direct-mount brakes at the chainstay are doing it for trend or marketing reasons. It’s a trend that may well disappear as road discs become more prevalent.

How much faster is an aero road bike? 

Are they the future? The experts’ views

Yes: Steven Fairchild, Fuji Bikes global product manager

“Direct-mount brakes are fractionally more aerodynamic because they sit closer to the frame, and they are more efficient because they help to get rid of redundant material in the frame design. Shimano hasn’t come out with any performance figures, but I’d say they must be stronger and stiffer than regular calliper brakes, too. Does that translate into an obvious benefit for the rider? I really can’t say, but logically they have to be stronger and stiff.”

No: David Alexander, Specialized Bicycle Components University, Body Geometry FIT expert

“Post-mount brakes may be fractionally better than existing calliper brakes in terms of power, but they’re not really any better for all-weather ability, they’re not really much better from an aero standpoint; and they’re not really much better in terms of power modulation. We do have post-mount brakes on a couple of our bikes and as a brand we certainly would never say no to any type of braking system, but we think road disc is the way forward.”

  • David Bassett

    The disc will outperform a calliper in the lab. But bike races happen on the road. It does not matter how good they are if you cant service a rider.
    Cyclo cross and personal riding is the only place for them. At this time there is no way they will work in a road race. Unless Shimano or someone gets a wheel to change as quick as a bike with calliper brakes.

  • Andrew Bairsto

    We do not all know a disc brake will outperform a calliper brake I for one very doubt overall it will.

  • trummy

    I am not quite sure what this is all about but if I have got it right then the rear brake is mounted direct on the chain stays?. If that is the case then I would look back at the Shimano dynamo which was mounted on the chain stays next to the bottom bracket. Great light, very low friction from the roller that ran on the centre of the tyre.But once it was used in wet weather it didn’t last 5 minutes! Not the place to mount a brake if you want to reliably stop in wet weather and expect a decent life out of the wheel rim.

  • Philip Notley

    it wont be beyond the wit of manufacturers to design a quick release disc wheel to over come this niggle a hydraulic disc is mind boggling good

  • William Keys

    If you pay attention to the MTB side of the world, you would know that companies are working on thru axles that pop in and out even more quickly than a QR. Also, with the thru axle the wheel alignment is set so the issues with setting/aligning pads is moot.

    Honestly, the great thing about thru axles is the repeatability of alignment. It makes life easier on mechanics because there is no chance for a wheel to go in mis-aligned. It will take away those dangerous derailuer and brake adjustments on the move during races as the new wheel will be perfectly aligned every time.

  • David Bassett

    And using through-axel you are joking. Aren’t you?

  • David Bassett

    You can not use a van In Road Races it is above the max height allowed. And what happens to the other rider that punctures whilst (and maybe rotor/pad alignment reset if needed). It is hard enough to swap wheels around on racks, keeping you supplied with good wheels in the car to use when a rider punctures
    Would I be wright in thinking your comment re resetting pads was a bit tong in cheek,

  • David Bassett

    That is what the team mechanics say they need to do in races. Just imagine getting a wheel in and out using disc wheels

  • disquzting

    “Fitting a rear brake underneath the chainstays has the effect of the wheel trying to rip the rear brake off the mounts. At least if you put the brakes at the top of the seatstays, the wheel is only trying to push the brakes into the seatstays, which is impossible.”……….

    doesnt seem to be a problem for decades with front brakes. and theyre the ones taking more braking force. nonsense worry.

  • blemcooper

    I assume he means it would be faster to switch bikes than to replace a punctured disc brake wheel that uses a through-axle.

    But presumably after swapping bikes, the support car could take the extra time to do that wheel replacement (and maybe rotor/pad alignment reset if needed) on the just-abandoned bike and put it back on the car for the next bike change, if it proves necessary.

    Perhaps team cars will switch from being small/mid-sized wagons to vans (American Flyers style?) so there could be an extra mechanic and extra space to deal with it on the move.

  • J1

    Why would you change bikes every time you puncture? Just get a new wheel. I don’t get where you’re coming from.

  • David Bassett

    We all know that a disc a brake will outperforms a calliper brake but you cant change bikes every time you puncture. You do see some unfortunate riders having several punctures in one race.
    Solution, a team will have to be made up of identical riders, so no problem of changing bikes, you just put nine identical bikes on the roof of the team car.