Friday, March 2, 2012

Disc brakes: Gnothi Seauton

When I've gone to the Mosaic shop Aaron has mentioned an online article about the complications and potential dangers of using disc brakes for road bikes a couple times.  I finally found the original article as well as a follow-up.

The Articles
The original article opens with the author's cautionary tale of a dramatic crash that resulted from complete brake failure on a road descent. The author was on a disc equipped Moots, which is a very similar setup to what I now have. The original article moves from this story to a discussion with several manufacturers about using disc brakes on road bikes (Shimano, TRP, Magura, Hayes). The article includes a discussion of why brake failure occurs and the challenges of using disc brakes on a road bike vs a mountain bike.

The follow-up second article is purely a discussion with wheel and hub manufacturers (American Classic, DT Swiss, Rolf Prima, Easton, Zipp, Reynolds) about the challenges and opportunities of building disc brake capable road bike wheels including a discussion of rims, hubs and spoke changes. While this discussion is interesting as a preview, there's nothing too alarming. The first article is a different story.

I'm still in love with the new bike. I've done a few more rides where I've begun incorporating some of the local hills on a route called Olde Stage Road. Recently I clocked 54 mph on the descent and the idea of brake failure at that speed is unappealing to say the least. The main difference (on the surface) in road vs mountain bike braking appears to be higher speeds and longer descents. This main issue is one of heat dissipation.  I won't rehash the article, but will say that talk of boiling hydraulic fluid and warped rotors is a little alarming. While I do think the author made an effort to be impartial in the presentation, I feel that without a close critical read, it could easily come off as alarmist. Beginning this tale with a major failure, and  a serious injury sets this tone.

Misinterpretation of purpose
This article does not provide, nor was it intended to provide, a discussion of the merits of using disc bakes as compared to rim brakes, on road bikes. Such a discussion could have offered a balanced presentation of the strengths and weaknesses of each system. Of these four topics which could be discussed (the pros and cons of disc, the pros and cons of rim brakes) the article mostly focuses on the challenges of disc brakes. Unfortunately, many readers are not cautious consumers of information. Reading this article understanding the purpose as "hey these disc brakes are kinda new for use on the road and they're not perfect. Here's some stuff you may not know, but should" makes it a brilliant piece of timely work that I was happy to find. Just remember it's only one part of the road bike brake discussion.

Comments worth reading
Reading the comments (which I recommend in this case) shows that many did not take this interpretation - something I cannot fault the author for. Many others who offered their comments provided useful feedback and valuable information. While most comments sections of popular articles quickly devolve into flame wars or tangent discussions, this very long list of comments provides a window into varying experiences and a picture of rim brake limitations, and disc brake benefits, which the article itself lacks. This might be the only time I'll say that the comment section is just as valuable to read as the article itself.

Lessons learned
I'm quite happy to have the information this article provides as I did learn a few things that may impact upcoming rotor/wheel purchases. If you're considering disc brakes on a road bike, this article and the follow-up are worth a read. Just makes sure you also know the strengths and limitations of rim brakes as well so you can be best prepared to make your own informed opinion. Disc and rim brakes each have their strengths and limitations: neither system is perfect but either should work fine when set-up and used correctly. Here's my summary of what I've gathered:

  • Rim brakes work and disc brakes work, but both can and do fail. 
    • Disc brakes can overheat, glaze and warp rotors in the right conditions leading to brake failure. 
    • Rim brakes can overheat, glaze and explode tubes in the right conditions leading to brake failure. Rim brakes on carbon rims or in wet/snowy/frozen/muddy conditions provide extra challenges. 
  • Disc brakes are newer in use on the road and there are some engineering challenges that have yet to be perfected. 
    • This is not to say, however, that we're in the stone age here. Current mechanical sysems work just fine, but many companies seem committed to developing road disc technology and within the next few years we will likely see a rapid evolution in products that at the very least reduce weight and may improve performance. (cf the SRAM Red hydraulic line slated for release Summer 2012 and the many ideas being floated here)
    • Current weights are undeniably higher in a disc brake system. There's just no room for argument or debate here - the extra spokes, rotors and heavier calipers make the system heavier. BUT the new SRAM hydraulics and the very recently announced Shimano road and CX mechanical disc brakes are shedding weight quickly. (e.g. my BB7s weigh 220g each while Shimano claim their CX75 at 156g - no small drop)
  • Operator error can be a major factor leading to failure. 
    • Like rim brakes, disc brakes are more prone to failure when used in a constant manner (continuous hold) rather than intermittent (i.e. fluttering or brake-release-repeat). A little education and awareness goes a long way here.
  • Equipment choice is important, and so is knowing where you're riding.
    • Small (i.e. 140mm) weight weenie rotors (Ashima, KCNC, etc.) do a poor job at heat dissipation. Using them for a high speed descent from the Col du Tourmalet may not be the best choice at this time. A larger rotor (160) with greater surface and heat shedding ability (e.g. Shimano IceTech or Avid HSX) would be a better choice. 
    • Using small, weight weenie rotors for a long flat ride regardless of speed, in a CX race, or in a situation where frequent albeit brief braking is the norm (i.e. gravel racing), is probably fine. 
Shimano's new CX75

Will it impact my equipment choice or riding? Perhaps.
I'm currently running a 160 front and 140 rear rotor and both are in or near the weight weenie category. I have no worries about using these for most of my riding, but may purchase a set of rotors that are better at heat shedding for use on routes with long fast road descents. As far as how I use the brakes is concerned, I can guarantee you that I'll be thinking of how long I pull that lever on long descents. 

My current front brake setup


  1. Good post, in the article the writers brake levers pulled all the way to the handlebars, a classic sign of fluid fade over pad fade. What that says to me is that with mechanical discs he would have still had brakes, and also that chances are he did a poor job bleeding the system.

    I have used my mountain bike with hydro discs on many long steep and fast road descents without a bit of fade. I am actually the type to see what it WOULD take to make them fade in a controlled manner just so I can know and even descending Rampart Range Rd dragging only the rear brake (160mm stock rotors) from well above the water towers down to the bottom keeping mostly between 25-30 mph did not even cause the slightest bit of fade.

  2. Thanks Chris. I hear plenty of stories about folks having no issues whatsoever with the hydro and mechanical discs. It's good to know that problems can happen (as pointed out in the article) but also important to realize that this is a situation that can be avoided. Unfortunately, it's too easy to see this as an alarmist message along the lines of "oh my god disc brakes will kill you on a fast road descent!"

    The only problem I've had is getting used to the modulation in different conditions! I can pretty easily lock up the rear on a sandy, loose, fast descent - which happened a couple times yesterday. Of course that's totally an operator issue and after doing that once at 40mph I was a bit more ginger after realizing that the soft surface killed my traction.

  3. Sadly "alarmist" headlines draw more readers, not many would be interested in a headline that read "disc brakes work as they always have"

    Modulation is certainly different, good or bad can be debatable but I really like it. They have quite a bit more power than canti's, even when I had a set of Paul canti's they really lacked the power of discs or even v-brakes. If you have not had the pleasure of extremely long stutter bump filled descent yet you will really see where discs shine, your hands last quite a bit longer from not having to squeeze the brakes as hard.