Freewheeling: The Road Disc Revolution Is Now

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Of course Johnson’s slant is decidedly ’cross focused, where the impact of things like added weight and reduced aerodynamics are less profound. We don’t have full weights of the new SRAM system, but it’s reasonable to expect that swapping on disc brakes could add anywhere from 200 to 500 grams of heft to your rig. This number remains in flux in part because the industry is still trying to nail down what size disc rotors will work for the various applications, be them ’cross, gravel road riding, or going full monty, and dive bombing steep paved mountain roads at 55mph.

This is ample ammunition for some disc detractors, who remain unconvinced that change is for the good. “I think when people discover how much heavier [disc brake systems] are, and how much they detract from the aesthetic of what we have come to envision as the ideal form of a road bike, that is going to be tough for a lot of people,” said Mavic PR man Zack Vestal, alluding to the fact that a pair of 160mm rotors can easily weigh 160 grams. “I honestly think it is going to be more niche for more years than everybody is willing to admit at this point.”

Out of the gate, SRAM is recommending 160mm rotors for paved use and 140mm for off road. But others within the industry see those numbers as a still-moving target.

“Of course like everyone else, we are looking at disc and seeing where we should go with it,” said Cervélo founder and chairman Phil White. “The feedback so far is that you can’t do 140mm disc rotors, it has to be 160mm or maybe even 180mm. And that becomes a challenge for aerodynamics and weight. But certainly we are looking at road disc, we just but don’t have an informed position yet.”

It should be noted that White – and just about anyone who builds time trial bikes — is a fan of hydraulic rim brakes. Cervélo’s recently released its revamped P3 time trial bike, which is spec’d with Magura’s RT6 hydraulic rim brakes. The advantage, of course, is that hydraulic systems don’t encounter the same routing issues as cable-actuated brakes when it comes to navigating the circuitous shapes of TT bike frames. They also typically have a more aero shape, tucking inside the borders of frame tubing better than their cable-actuated cousins.

“Obviously disc brakes require some special modifications to frames, but hydraulic rim brakes can be mounted to anything,” said Charles Becker, SRAM’s category manger for road and triathlon. “With Hydro Rim Road you get a ton of the benefits that come with hydraulic braking even though it’s still a pad on a rim. The amount of hand effort required is much less, and you are totally freed from cable routing issues because hydraulic hoses don’t care what shape they are in. So a lot of these aero bikes with the very challenging routing issues can now easily be overcome, whereas a bad angle with a cable system can really effect the performance of the brake.”

Becker’s first statement, that disc brakes require some frame modifications, leads one to wonder how deeply the industry has already committed to this new technology. You would assume that the SRAM brain trust wouldn’t release new technology into a marketplace that’s not ready to accept it. And indeed, it appears that’s the case.

“We have been working with several bike manufacturers for two-plus years on this project,” SRAM’s Becker confirmed. “There are already many bikes that are ready [for disc brakes]. The bikes you see here [at the SRAM Red 22 launch at Sea Otter] are production Specialized Roubaix bikes. And of course cyclocross disc frames have been around for a while now. Most are mechanical, but they can certainly be converted to hydraulic.”

About the author: Jason Sumner

An avid cyclist, Jason Sumner has been writing about two-wheeled pursuits of all kinds since 1999. He’s covered the Tour de France, the Olympic Games, and dozens of other international cycling events. He also likes to throw himself into the fray, penning first-person accounts of cycling adventures in British Columbia, Belgium, Brazil, Costa Rica, France, and Peru among many others. Sumner, who joined the RoadBikeReview.com / Mtbr.com staff in January, 2013, has also done extensive gear testing and edited a book on cycling tips. When not writing or riding, the native Coloradoan can be found enjoying the great outdoors with his wife Lisa.


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  • Len says:

    Another solution in search of a problem.

    On-road, discs have always made sense on foul-weather commuter bikes, but that’s about it.

    Despite the fact that the industry is, as ever, amped about ‘up-technologizing’ the road bike so that it can charge us more $$$, most riders I know are not champing at the bit to try road discs. Or hydro braking either.

    • Harley says:

      I’ve been chomping at the bit for road bike disc brakes for over a decade.

      They have superior stopping power in all conditions; lighten the rotating mass of the wheel; stop rim wear; are mainly easier to maintain (imo); free the rim design from needing a pad contact area; etc. There aren’t many good reasons to stick with an inferior braking mechanism.

  • Jimbo99 says:

    Gonna be hillarious ? Changing brake pads is going to be like fixing a motorcycle. Why hydraulic, why not a self adjusting cable, like some clutches on automobiles have ? I can’t see me bleeding brake lines, that brake fluid spurting all over the frame of the bike and floor. This is just sheer genius ?

    • Gillis says:

      Jimbo99, I take it you’ve never owned a mtb with discs as your assumptions are totally off base. Changing pads doesn’t require bleeding. Heck, with modern systems you don’t even need to bleed but once a year or less. I had a older pair of Hayes that I didn’t bleed for over 3 years without any problems.

    • aclinjury says:

      don’t get the brake fluid on those pads or else they won’t brake.

    • jim says:

      nothey do it on MTB bike now. notany harderr unless wheile changing the pads out you grab the levers than u will need to bleed than

  • Abe Froman says:

    “It doesn’t happen often, but on hot days you will see a tire blowing under heavy braking due to the rim heating up.”

    In over 30 years and 250k miles of racing, training, commuting; this has happened to me or someone I know 0 times. Shows me how much of a problem it is. If you are using your brakes so much that it heats up the rim until something fails, I’d the the problem is with the person applying the brakes. You might cause the tube to fail with disc brakes; you will just heat/boil the brake fluid until the lever comes back to the bar and you have no brakes.

    I can see their advantage in wet weather conditions but on a clean dry road, I don’t see them having a significant advantage. Don’t need them or want them and I don’t go out of my way to ride in the rain.

    • Abe Froman says:

      That should be “you might not cause the tube to fail with disc brakes”

    • aclinjury says:

      The pro-disc crowds sure make a big stink about
      1) riding in the rain, when in real life most people avoid the rain, well except if you’re my gramp on his hydrib

      2) high speed descent causing the tire to blowout. Perhaps these folks just are not good bike handler, therefore perhaps they should just ride flat and skip the mountains?

      • Harley says:

        They’ll stop you faster in the dry too. This makes a difference when riding in traffic, around pedestrians on shared bike paths, etc.

  • Aaron says:

    Had a nice rain ride yesterday….discs would have been nice. Living in the Midwest though, with no mountains to speak of, wet performance would be the only benefit in my eyes. And as we previously mentioned, most folks avoid riding in the rain anyway so I can see why so many say it doesn’t matter to them. Now if I lived in a region with big, long descents….yeah, I’d like them.

  • Eric says:

    People tend to forget that you can overheat disc brakes too. The tire may not blow off, but the rotor can warp and really cause some issues.

    • Harley says:

      Yes, but with disc brakes the problem is less severe and more easily dealt with (e.g. you can swap to a larger disc if you’re overheating your smaller one often).

  • Ken says:

    I’ve been riding disk on my MTB (s) for over a decade. I’ve had XTR and Avid. Never had to bleed. Pad replacement is simple. Don’t know what all the fuss is about.

  • TA1200 says:

    As my experiences on my mountain bike show, disc brakes offer important advanges: they work more powerful and are easier to modulate especially in wet conditions and notably with carbon rims, brake power can easely be up- and downgraded with other disc sizes, hydraulic pipes break rarer than brake cables.
    Of course you also get disadvantages wich last less or more on your skills: 3/4-1 lb more weight per bike will slow ambitious climbers, they might cost as much as high end rim brakes (also the pads), not everyone is able to change himself pads nor brake fluid (every couple of years), the question of aerodynamic is a more one.
    The communities are: depending of your behaviour and technic, you may overheat both systems and get a failure, you have to avoid damages on disc and rim surface, brake power and modulation are also affected by quality of brake and pads, the less you and your bike weigh and the more broad-shouldered you are, the less you must brake.
    Heavy climbers will benefy considerious more from the safety advantages than light bikers who rarely leave the flats. Finally I will have to estimate if I would invest more money into this marvelous hobby at next bike change.

  • swami says:

    My ‘cross bike has mechanical discs. It’s heavy, partly because of the braking system. However, it’s most definitely my Swiss army knife. I use it to race cyclocross (I know, heavy). It’s my commuter. It’s my gravel grinder. At one time, it was even my century ride. Do I care that those discs add a pound+? At ‘cross races, sure. If I were uber-competitive, I’d definitely think twice about discs, and mechanicals of course suck (relative to hydraulics) for lots of reasons. BUT at those same ‘cross races, the modulation, the non-issues of mud clearing and wet braking, and sheer braking power/performance are all winners for me. Commuting, (I live in the Pac NW) reliable braking in the rain is a real win. Gravel? 1-finger braking and modulation going over washboard at speed is another win. If I were in the market for another Swiss army knife, I’d do hydraulics in a second – particularly given what today is probably just a 1/2-pound penalty. …but Road? I can see some benefits, but this is a technology that will need to shake out quite a bit and standardize before I’d make that jump. Of course I have a sub-16lbs road bike that I love – I am very much not in the market there. Even if I were? Even after years for exposure to the benefits of discs on a “road” bike, I’d be disinclined. There are times I’m too hot in the corners, and better modulation & braking power would benefit me – but not many. For me, all the other benefits don’t apply to road rides.

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