Tuesday, November 5, 2013

Hydraulic and Disc Brakes . . . Again.

I couldn't help but come back to this subject. I covered hydraulic rim brakes and disc brakes pretty thoroughly a while back. (Putting on the Brakes Part One, and Part Two) But I recently came across a couple of items on the subject that I wanted to talk about.

First: This article that just appeared in BikeRadar -- SRAM Stops Sale of Hydro Road Brakes. I went to the SRAM site, and here's what little they have on the subject (SRAM). But the BikeRadar article says that SRAM has asked manufacturers to stop selling bikes equipped with the hydraulic rim brakes due to an unspecified safety issue. For those already riding with the brakes, a recall is apparently in the works. I doubt too many people reading a blog called The Retrogrouch are likely to be affected, but if you know somebody with these brakes, have them contact their dealer and see what they need to do.

Next: Also from BikeRadar comes this video:

They're Coming!! Disc Brakes are Coming to Road Bikes! Can you feel the excitement?! 

Here are some highlights from the video. From Giant: "You absolutely do need them because I cannot think of another example on this planet where you can't have enough brake (that doesn't actually make sense -- Retrogrouch) . . . There's no such thing as too much brake. . . Obviously there are some hurdles -- to get it lightweight enough -- to get it effective enough for quick wheel changes -- to get it UCI legal -- these are hurdles that will be overcome in the next couple of years . . . and when all of those hurdles are overcome you're going to see that product everywhere." 

I think there are more hurdles to overcome than weight and the UCI. Like fade, and warped rotors -- more on that in a moment.

From SRAM: "The way people are riding their bikes these days - the consistency - the power - making sure they can ride in all weather conditions, I think it's going to be a great advantage for people. Once you try it, you'll adopt it." 

How exactly are people riding their bikes differently these days? And I have "tried it," and I'm not yet convinced.

From Storck: "It's definitely the future."

I can't wait.

From Focus: "There's always an overheating issue with carbon fiber rims and caliper brakes . . . it's one of the main reasons." (for going to disc brakes, that is)

Now THAT comment I can agree with wholeheartedly. I suggested in an earlier post (Get the Brakes Off the Rim and the Rim Won't Break) that one of the things driving disc brakes for road bikes is the fact that racers and weight weenies want to abandon very reliable aluminum rims in favor of shedding a few more grams with carbon rims -- but the braking on carbon rims is terrible, and possibly dangerous. Disc brakes help to avoid that problem -- but not without other problems that the marketing side would like to ignore.

Some of the spokespeople in the above video talk about the weight of disc brakes -- but the weight is not exactly the problem. People who obsess about weight want them to be lighter, but if anything, they need to be heavier. The real problem with discs is overheating, which can lead to fade and warped rotors. Lots of disc brake proponents claim discs don't fade like rim brakes -- but in fact, the opposite is true. 

The rep from Giant in the above video claims, "The advantage with disc brakes is they don't fade like a caliper brake." Even wikipedia makes this claim, "Disc brakes are less prone to fading under heavy or prolonged braking compared with rim brakes."(http://en.wikipedia.org/wiki/Bicycle_brake#Disc_brakes) Of course, that statement is completely undocumented and unsupported, and there is much evidence to the contrary.

First of all, functionally, rim brakes ARE disc brakes -- with a huge braking disc 622 mm in diameter. Most disc brake systems have discs only 140 - 180 mm in diameter. All things being equal, a larger disc is much better than a smaller one because it will heat more slowly, and dissipate heat much better. That's why performance cars have huge rims with the largest brake rotors that will fit.

The problem with rim brakes is that heat generated by braking on a long descent can possibly heat the tires to the point of a blowout -- a legitimate concern for loaded touring bikes or tandems -- but one that can be mitigated considerably by good technique. Disc brakes, being much smaller in diameter, can overheat much more quickly -- rising to much higher temperatures in much less time than rims. This extreme heat on disc brakes will not lead to a tire blowout, but it can lead to complete loss of braking. The pads can glaze over, or the brake fluid (if it's a hydraulic system) can boil. The discs, in order to keep them light, are very thin (only about 2 mm!), so the heat builds up very quickly and can even cause them to warp. Making the discs thicker can help with these problems, but that adds weight which racers and weight weenies don't want.

This article from BikeRumor (Road Bike Disc Brakes are Coming, But Will They Work?) describes exactly that extreme fade scenario, with an incident resulting in five broken ribs for the writer. In the BikeRumor article, there are comments on the accident and its causes from brake manufacturers Shimano, Magura, TRP, and Hayes. Ultimately, the experts (and even the writer himself) more or less agree that the problem in his case was poor technique -- holding the brakes too long on a fast descent, to the point where he lost all braking.

From Shimano: "Riders may need to brake hard for a short distance, for instance coming into and going around the corners, then let off so they can cool. I think in your situation, you were on the brakes the whole time and they simply got too hot." (Retrogrouch note: any experienced road cyclist should recognize that this is the exact same technique that riders on long mountain descents have used for years - brake hard for a short time, then let the brakes cool. So how, exactly are the discs any better?)

And the spokesperson from Hayes: "What we found with road bikes was that you can generate incredible heat and forces. There are long descents where you're dragging the brakes for a long time. You have tiny little calipers with very little thermal mass. And they have tiny little pistons that require very little fluid volume. Then you have tiny rotors with virtually no mass that can't dissipate heat. When you whittle everything down to a super lightweight package, the only place for all that heat to go is the hydraulic fluid, and you can boil it in no time at all. When the fluid boils, it happens instantaneously and it happens right behind the brake pads. As soon as that happens, it introduces air into the system."

So here we have people actually in the industry, discussing very real problems with disc brakes, that the marketing people ignore or completely gloss over. 

As for the writer on BikeRumor who broke five ribs when his disc brakes faded to nothing -- what exactly did he do wrong? If you ask me, he listened to (and believed) the marketing hype about disc brakes. More braking power! No fade! Safer! Sure, he rode the brakes too long on the descent -- but how many people wouldn't make the exact same mistake after hearing all the claims? When the so-called experts, and the marketing people, and the hype-happy cheerleaders at the big bicycle magazines keep shouting over and over that disc brakes are so much better than rim brakes, and don't suffer from fade -- who wouldn't think that they can drag the brake on a long descent without consequences? In the end, we see (and have it confirmed by those analyzing the aftermath of a terrible accident) that skill and technique are still important -- in fact, the same basic technique that we've always been using with the supposedly inferior rim brakes.

I do have no doubt that disc brakes are indeed coming to more road bikes, but I hope they get a lot better than they are so far. And I don't think I'll be adopting them any time soon. Until they can solve the real problems with disc brakes, I haven't seen anything so far that leads me to believe they are significantly better than good rim brakes.


  1. I believe disc brakes are the future. I'm old, I live happily in the past.

  2. After trying them on my new bicycle, a Trek Crossrip Elite, I've discovered how much a road tire can get stuck in wet asphalt. Next year I'll travel around Europe, from South to North and back to home, with a lot of gear; then I could tell my experience on long descents; but for now they're working better than rim brakes.

    That said, we've been cycling for ages without disc brakes, over water, mud, sand, snow... We definitely don't NEED them.