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 12^th or 13^th, if I remember correctly.  And plenty of others were available.