Mid-Life Cycling

Mid-Life Cycling

03 October 2015

Mature? Not Yet: Disc Brakes On Bicycles

In the mid-1970s, my high school acquired its first computer.  The father of one of my classmates, who worked in a nearby military base, in one of those jobs he couldn’t talk about, negotiated the purchase.  For $6000, my alma mater got a used machine, about half the size of a classroom—and with about half of the capacity of devices kids carry in their backpacks nowadays.

When I graduated the following year, one of my relatives gave me a new Texas Instruments Model 101 digital wristwatch.  With its red LED display and sleek goldtone band, it seemed like the epitome of elegance and slick high-tech, all rolled up into one.  No one else I knew had such a timepiece:  For the one and only time in my high-school years, I was the coolest kid in the class.  At least, that’s how I felt.

Neither the computer nor my watch made it past my sophomore year of college.  The big box (“It’s just an oversized, overpriced file cabinet!” one parent exclaimed upon learning what it cost) assigned classes like “Sports Heroes” to honors students who signed up for the Shakespeare seminar.  (I know.  I was one of those students.) And that was the least of the computer’s malfunctions. Worst of all, nobody seemed to know how to fix them.

And nobody seemed to know how to fix my watch.  One shop claimed that displays of numbers that had nothing to do with the time of day were a result of “water damage” –only moments after I took that watch out of its box.  (I have since learned that technicians and reps say “water damage” when your electronic device is acting up or not working and  they can’t figure out why.)

Less than a decade after I graduated high school, the Yankees were giving away digital watches (with the team’s logo, of course) as promotional items on Fan Appreciation Day. My graduation gift, in contrast, sold for more (in non-inflation adjusted dollars) than most smartphones or laptops cost today.  And the watches the Yankees gave away were more reliable (water resistant to 100 meters, and shock resistant) than the one I got on Graduation Day.   

I was thinking about the computer and watch as I read an article in the most recent Bicycle Quarterly.

In “Are Disc Brakes Mature Technology? “, Jan Heine recounts his and other BQ editors’ experiences with both mechanical and hydraulic disc brakes on road, mountain and city bikes.  While the brakes on one bike offered the power and modulation of good caliper brakes, their performance was hampered by their incompatibility with the levers that came on the bike.  The brakes on the other bike were not as good as road calipers and, worse, there were a couple of potentially serious failures. 

Heine seems to think that disc brakes have potential, but there are issues that need to be worked out.  Braking power is still determined mainly by the size of the disc.  A larger disc is heavier and could necessitate larger forks—both of which are anathema to racers and other performance-oriented cyclists.  More important, though, is that while larger discs offer more power, they seem to offer less modulation.  From what Heine and others say, it seems that larger rotors give the brakes the “all or nothing” feel that V-brakes (at least the ones I’ve used) always seem to have.

Avid BB7 disc brake on Look X85 cyclo-cross bike

The flip-side is, of course, that smaller rotors offer less power.  And, if there isn’t enough power, whatever modulation the brakes offer is all but irrelevant.

Another problem, as Heine points out, is that on disc brakes, the pad grabs the disc on the rear.  On a front fork, that means the wheel is pulled away from the dropout (or fork end).  When you’re barreling down a hill—or sluicing through traffic—few things are more dangerous than a front wheel popping out of a fork. 

Most modern quick release levers, Heine says, aren’t secure enough for bikes with powerful disc brakes.   Through-axles, like the ones found on downhill bikes, might be a solution.  But even with them, the fork blades on most non-suspension (telescoping) forks wouldn’t be stiff enough to counter the forces the brakes would put on them.  So, Heine says, a dedicated suspension fork might be the best kind to use with disc brakes.

 (In contrast, rim brakes pull the wheel slightly upward, into the dropout.  And their forces are concentrated in or near the stiffest and strongest part of the fork:  the crown.  That is the reason why properly-installed wheels don’t fall out of forks equipped with rim brakes or no brakes.)

I myself don’t plan to start using disc brakes any time soon:  I have never had trouble getting the braking power and modulation I need from rim brakes, as long as I use good cables and pads and keep everything properly adjusted.  Plus, there is something to be said for the simplicity, not to mention the lighter weight, of such brakes.  So, I hope that disc brakes don’t become the only option on new bikes or that component manufacturers stop making rim brakes and parts.

On the other hand, I am not against some bikes coming with disc brakes, or for such brakes to be offered on bikes where they might make sense.  Most of all, I hope they don’t become a de facto standard—or the only option—before they are a “mature” technology.  At least, when my digital watch failed, I still had the mechanical watch another relative gave me for a birthday—my 12th or 13th, if I remember correctly.  And plenty of others were available. 


  1. Good post, Justine. My full-suspension mountain bike has hydraulic disc brakes, and I like them a lot for that particular type of bike. However, rim brakes are just fine on my commuter and road bikes. Disc brakes on road bikes is the next big (unnecessary) thing.

  2. Good post, Justine. My full-suspension mountain bike has hydraulic disc brakes, and I like them a lot for that particular type of bike. However, rim brakes are just fine on my commuter and road bikes. Disc brakes on road bikes is the next big (unnecessary) thing.

  3. MT--Thanks. If disc brakes make sense on any kind of bike right now, it's probably a full-suspension mountain--or downhill--mountain bike, especially if the wheels have through axles. Disc brakes might also make sense on a non-racing tandem bike. But for any other kind of bike, disc brakes--at least in this stage of their development--are unnecessary. I'm not sure they'll be of any benefit on road bikes.

  4. Maybe I'll get a disc brake bike in another 10 or 20 years...

  5. I totally agree. Anything but disc brakes on a high-performance mountain/downhill bikes is just silly. I suppose they make sense for cyclocross as well, but for everyone else it just adds complexity and cost. As for me, my Steamroller nearly stops on a dime with some old Dia Compe 610's and high quality pads.

  6. 50 Volt--I probably won't ever buy a downhill bike, and it's not likely that I'll buy a high-performance mountain bike. That's the real reason why I don't think I'll be using disc brakes any time soon.

  7. I ride road bikes exclusively (mostly a fixie), and I've been experimenting with a front disc brake for the past couple of years. I also read BQ, and I really think that what Jan Heine says needs to be taken with a heavy grain of salt. My experience has demonstrated that a good front disc brake is far superior to a good rim brake in terms of power, modulation, and reliability/durability, and especially in the winter. A front caliper will wear out the front rim, especially in the rain. Rims these days are being made with thinner sidewalls, so where I used to get three winters out of an aluminum rim (700C), I now get maybe one or two (I ride lots in the winter). As the front clincher rim wears, the sidewalls start to splay out, leading to "grabbing," irregular brake feel, fork "juddering," and eventually catastrophic rim failure. But usually you've replaced rims before then! On a disc front wheel, the rim never wears out, and a good metallic compound set of pads will last over 3,000 km. Organic disc pads are useless, they'll go maybe 500 km in a dirty,wet environment. I have used mechanical (BB7) and hydraulic (TRP Hydrex and Shimano 785) road discs and have been happy with all of them. I'm currently using a 785 caliper with TRP lever on my fixie this winter, and I'm having a new road bike built that will use a TRP Spyre mechanical caliper with Campag Ergopower lever. But, like my fixie, the new geared bike will use a rear caliper for weight savings, and because I hardly touch the rear brake when I've got the disc in front. So, yes, I think road discs are - if not mature - useful now, especially if you ride all winter.

  8. Attila--Your point about riding a lot in the winter is well-taken. And you're right about the thinner sidewalls of today's rims: That's where a lot of the "weight savings" really is.

    About Jan Heine: I don't take his word as gospel, any more than I take, well, the Gospel as gospel. (I hope I didn't offend your religious sensibilities, if you have any!) I do enjoy looking at BQ, though, as it offers articles and photos of things not covered in most cycling magazines.

    (I must say that I have issue with him and Compass Cycles appropriating the Rene Herse name. That's one reason why I haven't bought anything from Compass yet. Plus, I think a lot of their stuff is overpriced.)

    1. It would be very difficult to offend me! I think people are perfectly entitled to their opinions, and I respect where they differ from mine. One of the former Sony CEO's, in his autobiography, wrote about how he (when he was a vice-president) and a fellow vp would often be in disagreement about most issues. This other vp was bothered about this, and brought it up. The future CEO's response was, " well, if we both always agreed, why would the company need both of us?"
      As far as the gospels, I find it hard to believe that otherwise intelligent people would have such an irrational belief in some magic invisible guy up in the sky, even when he fails to solve any material problems in the world, or lets bad things happen to good people, I do admire Pope Francis, though, but primarily because he reflects the real teachings of Jesus, not those perverted by the fanatical Paul, upon whose letters much of the Catholic Church is based, despite often being at odds with Jesus' principals. So I hope I haven't offended your religious sensibilities!
      I agree that Compass stuff is quite overpriced. I'm used to buying Vredestein TriComp (now Senso) tires, which normally go for about $70, for $32 when they're on sale. I'd like to try the Compass 700x26 extralight tires to see if they do make a difference, but NOT for $75 a shot! I usually buy his more useful books when I can get them at distressed prices. Yes, and the current Rene Herse bikes are merely Boulder bicycles, no particular cache there.
      I have a hard time with his idea of "planing." I've read the article he linked me to regarding the physics behind it, but I remain unconvinced about how rotary crank motion can be stored and converted to forward motion of the bike. I am more inclined to believe that "planing" has more to do with using wider tires with thin sidewalls and lower pressure, where the tires get compressed at the start of the stroke, and somehow return "power" as they assume their regular shape. But I am not an engineer or physicist. I think power is lost as the tires compress, much like a mtb with front suspension that's not locked out.
      I do admit to reading BQ, though. Gives a refreshing perspective vs the usual bike mags!
      - Luis (Attila is just an alias)

  9. Luis--Truthfully, I have no religious (as in organized religion) beliefs and only the merest semblance of anything anyone might call faith or belief in a higher being. So about the only way anyone can offend me is by professing faith but behaving hypocritically.

    (I think now of the student who tried to "save my soul". I caught her cheating, and trying to help another student cheat!)

    Your comments about Heine's explanation of "planing" make sense to me. While I respect his experience and expertise, Jobst Brandt has always made more sense, to me, in explaining anything technical.

  10. My main complaint about disc brakes is the tight tolerances involved. It's so bad on one of my bikes that there's no room between 'able to pull the levers to the bars' and 'squeals constantly,' even with caliper realignment. Rotors are easier to bend that properly-built wheels and don't have to bend very far to scrape the pads on every rotation.

    I'm replacing those Avid BB7s with TRP Spyres, which I've had better luck with on another bike.

    Also, the need to use needle-nose pliers and Torx/tiny hex wrenches seems odd.

  11. Neil: Needle nose pliers and tiny hex wrenches? That, for me, is almost reason enough not to use the brakes!

    Although I am a bit more fastidious than most people about maintaining my bikes, I don't want to use overly fiddly equipment. When it's a nice day, I'd rather be riding than fixing. Also, I like equipment that's forgiving. For example, I want brakes that will still work even if, say, a spoke breaks and a wheel goes out of true or a derailleur that will still work even if the cable needs adjustment.

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