Wednesday, June 1, 2016

GPs Thoughts on Disc Brakes

I saw this post on the Rivendell Blug not too long ago about disc brakes vs. rim brakes. Needless to say, Grant Petersen says a lot of the same things I do about disc brakes, but with his years of experience in the business, he still has a way of saying them with a certain authority that I simply don't have.


If I could summarize Petersen's view on disc brakes, it is that there's nothing exactly wrong with them, but they aren't the vast and remarkable improvement over good rim brakes that the industry has been pushing for the last few years. In other words, they don't make bikes with rim brakes obsolete, and shouldn't.

Petersen points out some of the benefits of disc brakes -- notably the fact that they are less affected by mud and water, and that they don't heat up rims to the point of tire blowout on scary-fast descents.  Then again, for the majority of cyclists and conditions, those benefits are over-sold. And on the down-side, as he adds, the leverage of a disc brake concentrates a lot of force near the hub, putting a lot more stress on seat-stays, and on fork blades far from the crown. As a result, frames need to be beefed up in those areas, which can affect compliance and comfort. He also mentions how those braking forces concentrated out at the frame ends have been enough to overwhelm quick releases and even "lawyer tabs" on front forks, necessitating the move to through-axles. To wit, he asks the question, "Which is better -- a mechanical system that localizes stress on a small area, then bullies it into submission with bulk and beef, or one that disperses stress and spreads it out?"

He goes on to say, "Disc brakes are fine, but if the bike could speak for itself, it might request a rim brake. . . The fact is, rim brakes are getting pounded these days, but it's a kind of artificial pounding by fashion and commerce."

I would have to agree with that. I mean, if I were looking at a new bike on the showroom floor and the bike I wanted came with disc brakes, I certainly wouldn't reject it for that reason. But at the same time, I wouldn't be drawn to a particular bike because it had discs. And if there were another bike basically the same but with rim brakes, and selling for a lower price, I'd probably choose to save the money.

But there's another point to be made that resonates with me. And that is regarding the simplicity of a traditional rim brake. Everything is out in the open, easy to see and easy to maintain, while potential problems are easy to diagnose and solve. Some would likely point out that once a modern hydraulic disc brake system is set up properly, it needs little maintenance. To which I would respond that getting it set up properly is a lot more likely to be something that requires an experienced mechanic, and if something actually goes wrong (and things do, indeed, go wrong - even on the best of systems) it can be a lot harder to diagnose or solve. This is something I wrote about last year when a bike reviewer for BikeRadar had a pretty scary disc brake failure on a test ride. In that case, the brake components were sent back to Shimano for inspection, but ultimately, even they couldn't adequately explain how or why the failure occurred.

Petersen describes it like this: "Ultimately, you can expect the bicycle of the immediate future to become more of a high tech black box, with cables being replaced by hydraulics, and the visible levers and pulleys and other simple machines that combine into bicycle magic being hidden or replaced by electronics. The bicycle of the future will, absolutely, be shrouded in mystery and sold on reputation and faith, like a Samsung flat-screen TV."

He continues, "There's a tendency to trust mechanisms you can't see more than those you can, because when you see how something works, you see also the potential for failure. . . If you're mechanically adept you might be more attracted to something you can figure out and fix, but more people aren't that than are."

That really nails it for me, and it's something I've touched on again and again in this blog - whether it's electronic shifting, or disc brakes, or integrated/connected dashboards and other electronic gewgaws -- all that stuff makes the bike more of a "black box" (I like that description, so I'm using it) and takes it further from the simplicity that I value in a bicycle. Fly-by-wire electronic and hydraulic systems, for efficiency, comfort, and safety, all controlled by a state-of-the-art computer is fine for my car. But what makes a bicycle special is that it demonstrably doesn't need any of that to make it any better.

People do seem to like push-button/touch-screen convenience, which oddly enough seems so simple, but only because the far greater complexity is kept hidden, and only accessible by those who are specially trained and certified to look behind the plastic covers. That illusory simplicity is great when everything works as it should, but vanishes into the ether when something goes wrong. It's like a microwave oven. If something goes wrong, it ends up costing more to fix it than to just scrap it and buy a new one. Bikes and bike components shouldn't be that.

In the end of Petersen's blug post, he concludes by saying "Don't dis the rim brake. It's beautiful and it works, and today's rim brakes are better than ever."

Couldn't agree more.

17 comments:

  1. As you know, Jan Heine had a pretty hairy descent while testing a Specialized Diverge because the disc brakes malfunctioned. I don’t trust them.

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  2. I, too, read Grant Petersen's post with great interest. Disc brakes are a solution in search of a problem - great for marketing but not necessary for the vast majority of cyclists. I would avoid a bike if it came with disc brakes - I've spoken to a couple of friends who have had disc brakes lock up on them. Has that ever happened with a rim brake? I don't think it's even possible.

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  3. Misses the point entirely. Disc brakes allow the use of large 42+ mm road tires. Modern groups limit road tire size to 28 mm. This larger tire more than makes up for the comfort lost by reinforcing the frame. In addition, there are excellent mechanical disk brakes: see, for example, Paul Components Klamper.

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    1. Misses the point? No. Tire size is simply a different point.

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  4. I would expand on Bruce Indy's comment and say that the infatuation with disc brakes is concurrent with the infatuation with an unprecedented selection of tire and rim sizes, as if to say, if you change this here, what happens there? Can you swap this set for that set? As with the relative merits of discs, the discussion is often of a theoretical nature, the sort of discussion that arises when one group of people tries to convince another group of people to buy new things. One's actual needs rarely enter into it. A sure sign of a nouveau-riche mark is how overbuilt all his or her belongings are for how they are used—kitchens, cars, electronics, and yes, bikes. It takes a great deal of self-assurance in our culture to make do with good enough, it seems. I bought a used bike with discs recently in part to see what the fuss was about. My current opinion is that the necessary beefing up of the frame does have repercussions in reduced feel. In the case of Rivendell, eschewing discs is both a philosophical and a business stance, since retooling would be quite an investment, and customers are pretty irrational as a group and tend to move in groups. In a year or two, in-line cantilever brakes will probably once again be a revelation, and the prevailing view will be that we all really should make up our minds about tire size and be done with it. For all we know, proportional tire size for frames and scaled-down domestic adventures will win the day, and at that point, so will Grant Petersen.

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  5. I've used Avid cable disc brakes on the last 3 of my dirt road bikes (Redline Monocog 29er, Fargo, and current custom) and I know that they do provide some real benefits; whether these benefits outweigh the disadvantages depends on the user's priorities, but no one can deny that they do have benefits.

    Perhaps the principal benefit, for my needs, is that they don't require brake tracks on the rim, so that one can use very light disc only rims: my 700C Velocity Blunt SS's have claimed weight of 430 grams (Open Pro weight) and, with (actual) 360 gram 700C X 50 Furious Freds run tubeless, the wheelset are amazingly light and really transform the ride, compared to the earlier rims and tires.

    Secondly, one doesn't worry about wearing out rims from braking in sandy or muddy conditions -- not a small consideration when your rims are quite expensive.

    And then of course you have the commonly noted advantage of consistent braking in wet or muddy conditions.

    One more advantage, for my purposes, is that I can easily swap between 700C X 50 wheels and, say, 650b X 70s. Sure, most people don't care about swapping wheels, but some do: my present Matthews was deliberately designed to take 622 X 60s with fenders, 584s X 70s, and 559s X 77s.

    I believe that, when you are running 50 mm or fatter tires at 25 lbs or less (I run my FFs at about 20-23 for combined dirt and pavement riding), a stiffer fork makes little difference to ride feel.

    I agree that discs are simply added complexity for many riders, but no one can deny that they have real advantages. Whether one prefers these advantages or not is a matter of personal preference.

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  6. What a great discussion. My principle objection to disc brakes is that they are just ugly. On a car they are at least hidden under the wheel (sort of), on a bike they are hanging out for all to see.

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  7. Discs are okay. If you want them on your bike, nice, feel free to choose what suits you best.

    The problem is marketing policy that tries to convince that rim brakes are unacceptable any more. I've never had any problems with stopping in any situations with rim brakes. If you constantly need to block the wheel, you certainly doing something wrong on the road. Does anyone remember good tip by rally legend Richard Burns? If you constantly missing the line, if you enter the corner lately and struggle to turn and gain the speed in the corner's exit, you're driving too fast. Brake early and your stage time will increase rapidly.

    The main safety device is being placed not where the brake mount is. The main safety device is in your head. Read the road situation and learn how to predict. No wonder-brake system makes you any safer. It merely shifts the threshold closer to extremes.

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  8. I dont want that crap on my car either! Everything will fail at some point and these black boxes cost a lot to have fixed. I dont even want power door locks and windows! As for my bike, I WANT simple lo-tech: friction shifting, rim brakes etc. because it works and keeps life simple. As does my Pentax Spotmatic.

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    1. Doesn't your Spotmatic need a battery? Or hydraulic fluid?

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    2. I believe that your Spotmatic requires a battery for TTL metering (like my Minolta SRT) a mercury battery that isn't made anymore. Unless you just use Sunny 16 ;)

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    3. Yes, the classic Spotmatic requires a battery. And yes, there is a workaround so that current batteries can be used.

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  9. Disc brakes are stupid on pure road bikes. However, once the component manufacturers figure out the engineering on good hydraulic shakes and road calipers, the recreational market can benefit greatly from disc brakes. Ironically, the type of bike best suited to disc brakes is the hybrid or enduro-allroad bikes like Rivendells: You have a lot of tire clearance, and you can switch between big tires on a 26er or smaller 650bs, or even 700c road wheels depending on your ride. You can set up your bike with tubby (tubeless!) rubber for your grinduro gravel adventures, or skinny tires for that charity century with your spouse. With Disc brakes, you can have one bike that does it all.

    NB: The assertion that the flexibility of the fork adds suspension is wishful thinking at best. Fat tires and flexy bars help much more than noodly forks. Remember: The fork is the part of the bike that keeps your teeth in your head. It needs to be strong first.

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  10. Disc brakes are very good on riv style hybrids and the enduro-allroad fat tired bikes that Jan Heine is so enamored with. They allow for light weight fat tires, multiple wheelsizes depending on terrain, reliable stopping in bad weather, and flexibility in tire sizing. Disc brakes do nothing to improve traditional road bikes, but there are some very good use cases, and many of them are on Rivendells!

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  11. Both Paul and Heine offer center pull brakes that accommodate large (42 mm) tires. If you keep a constant rim size, you can interchange wheels very easily. Disk brakes require stiffening the frame, to the detriment of comfort. I think you will see innovations in frame design to combat that, a la Trek Domane.

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  12. I share your views on disc brakes, particularly their need for expert set-up and maintenance. I've never had them on my own bikes, but my son's fancy mountain bike has hydraulic disc brakes and I became a lot more skeptical after needing to make a trip to a bike shop to have them bled. That said, a friend who puts on LOTS of miles has come to love them: they work well in the rain here on the wet coast, and he used to wear out a set of rims in less than a year, and now no more.

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