Myth 12: Disc Brakes Work Better Than Rim Brakes

To celebrate Bicycle Quarterly‘s 15th anniversary, we are looking at myths in cycling: things we used to believe, but which we’ve since found not to be true.

Disc brakes have become popular on allroad bikes for a variety of reasons. One of them is that they are perceived as offering superior braking. It seems to make sense – after all, disc brakes on cars and motorbikes revolutionized braking performance. Why wouldn’t they do the same on bicycles?

On motorized vehicles, disc brakes replaced drum brakes that enclosed the braking surface inside a drum. The heat generated by braking had to go through the drum before it could reach the cooling air. During vigorous braking, the brakes got hotter and hotter, until they ‘faded’ – braking power was lost as the friction between pad and drum decreased.

Disc brakes solved this problem: The braking surface is exposed and cooled by the passing air as the motorcycle/car moves forward. And disc rotors are lighter than drums, so they can be larger, which increases the braking power further.

Why doesn’t this work for bicycles? If you’ve ever ridden a bike with drum brakes across hilly terrain, you’ll know how dreadful they tend to be: mushy in feel, and on long downhills, the braking power fades away almost completely. That is why they never became popular, especially since the bicycle’s rim provides a convenient brake rotor.

That’s right: Rims brakes are disc brakes. Most bicycles have had disc brakes all along. Using the rim for braking makes a lot of sense: The braking surface that is as large as possible, and since it’s (usually) made from aluminum, it dissipates heat quite well. Using the rim for the dual purposes of supporting the tire and braking saves weight, too.

However, there is a problem with rim brakes: The caliper has to reach around the tire (and fender). The wider the tire gets, the beefier the caliper needs to be in order to avoid flex that robs braking power.

For that reason, rim brakes work great on racing bikes with narrow tires (above), but many rim brakes for wider tires are poor stoppers. This gets worse in the rain, because the pads need to cut through the layer of water coating the rim to get any braking power at all. Many rim brakes for wide tires are too weak to do this quickly, so in the rain, you end up with almost no braking power at all.

It’s important to remember that this isn’t a problem with rim brakes in general, but with brake caliper flex. Unfortunately, there are few well-designed rim brakes for wide tires.

There are ways around the flex issue. Instead of beefing up the caliper until it gets so heavy that nobody wants it on their bike, you can use the – very stiff – fork and frame as part of the brake. Cantilever and centerpull brakes do that, and well-designed ones offer plenty of stopping power, even in the wet.

The calipers of disc brakes only reach around a thin brake rotor, so they can be made stiff with relatively little effort. This means that even inexpensive disc brakes usually offer adequate stopping power. Because the rotors are smaller than bicycle rims, disc brakes have less leverage over the wheel and need to clamp the rotor much harder than a rim brake. This has the positive side effect of wiping water off the braking surface quicker than many rim brakes.

Due to the small rotor and thin pads, disc brakes tend to bite earlier, offering more braking power during the initial application of the brake. As a result, many riders believe they have more power.

So what’s not to like on disc brakes?

  • Disc brakes tend grab: For the same reason that disc brakes bite early, they tend to be grabby at low speeds. Not a huge problem unless you do U-turns.
  • Mechanical discs lack power: Hydraulic discs offer great stopping power, but mechanical discs tend to have a lot of flex in the mechanism that translates the brake cable actuation into a clamping force on the disc rotor. Large rotors can make up for this deficiency, but few bike makers are spec’ing rotors large enough to match a really good rim brake. I have yet to ride a bike with mechanical discs that can lift rear wheel during hard braking (with the rider shifting their weight all the way back).
  • Weight: Rim brakes are an elegant solution, as they make dual use of the rim. Discs use a separate rotor, plus very stiff (and heavy) calipers, which add weight.
  • Loads on fork and spokes: Disc brakes transmit all the braking forces through the wheel and fork legs, so both must be stronger. I don’t have enough miles on my disc brake bike to tell whether the front-wheel spokes fatigue more, but we already know that disc brake forks need to be stiffer, which means they absorb fewer shocks.

 

All these disadvantages aren’t really an issue on many bikes, especially those with wide tires. Compared to cheap rim brakes, inexpensive disc brakes offer more power and better bite. The extra weight of the rotor can be mitigated by using carbon fiber rims, which are lighter. And modern carbon forks are stiff anyhow – carbon delaminates if it flexes too much – so adding disc brakes doesn’t result in a loss of shock absorption.

And yet, on a bike optimized for performance, rim brakes often remain the better choice. The best rim brakes are lighter than discs, while offering plenty of stopping power and more linear modulation. They allow for flexible fork blades that improve comfort and speed by reducing suspension losses. And the (much-thicker) pads tend to last longer, too.

Mountain bikes are a different issue: Hydraulic disc brakes have the added advantage of requiring less hand force during long descents on really rough terrain. And suspension forks combine stiff legs with shock absorption, thus eliminating one of the main disadvantages of discs on allroad bikes.

In conclusion, I think disc brakes are here to stay, at least on bikes with wide tires. (They make little sense on racing bikes with narrow tires.) Rim brakes will continue to have their place on high-end road and allroad bikes. It’s a bit like steel tubing, which you still find on some of the very best bikes, but on mid-range models, carbon now offers better performance.

Originally, we planned 12 articles in our ‘Myths in Cycling’ series, but as we’ve reviewed 15 years of Bicycle Quarterly, we realized that there are more myths than we thought, so we’ll continue this series for a while.

Further reading:

About Jan Heine, Editor, Bicycle Quarterly

Spirited rides that zig-zag across mountain ranges. Bicycle Quarterly magazine and its sister company, Compass Cycles, that turns our research into high-performance components for real-world riders.
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113 Responses to Myth 12: Disc Brakes Work Better Than Rim Brakes

  1. John Collier says:

    Disc brakes replaced drum brakes on motorcycles due to a disc brake’s linear relationship between lever force and resulting braking force. Drum brakes have “self-energizing” designed in. This makes for stronger braking force but there isn’t a linear relationship between lever force and resulting braking force. This makes powerful drum brakes difficult to modulate in sensitive situations, such as braking into a corner.

    Disc brakes became popular on bicycles due to excessive pad and rim wear while mountain biking in muddy terrain. It was not unusual for riders to carry spare brake pads during a ride, and rims had to be regularly replaced.

    Mechanical disc brakes do not work as well as hydraulic disc brakes due to internal friction. They are basically a giant screw thread and internal friction increases as braking force increases leading to a weaker, non-linear response (a spongy feeling).

    As you have pointed out, rim brakes are already light, powerful and easy to modulate disc brakes. I see no need for modern disc brakes on a road bicycle.

    • Benz Ouyang says:

      For more information on why motorized vehicles went to disc, read up on Jobst’s take on the subject. Jobst worked as a design engineer at Porsche on their F1 program, so he had front row seats on this development. https://yarchive.net/car/drum_brakes.html

    • Peter Trasko says:

      This is a minor point, but it comes up often. Rim brakes are not disks.

      Yes, a rim is similar to a disk rotor in that they are both metal circles squeezed by a caliper of some kind. But there the similarity ends.

      Disk brakes work by having a very high mechanical advantage. This means that for a given amount of cable travel, the pad travel is very low. The result is that a given hand effort creates an enormous force at the rotor. In order for the rotor to sustain this force, it must be a solid piece of metal. That’s the first difference between rotors and rims: rims are hollow, and could not sustain such forces without buckling.

      Disk brakes’ high mechanical advantage / small pad travel means that the pad must be placed very, very close to the rotor. For that to work, the rotor must be perfectly straight and true. That’s the second difference w/r/t rims: rims are never quite true, plus they flex side to side in hard cornering. They can also be easily thrown out of true by minor bumps and mishaps, and a good brake needs to be spaced off far enough to allow that wobble.

      The relevant qualities for a disk rotor are that they are a solid, straight, and true. They need to be this way to deal with the great forces acting on them. The fact that they are metal circles, “just like rims” really isn’t relevant.

  2. Frank says:

    “Compared to cheap rim brakes, inexpensive disc brakes offer more power and better bite.” Hm, I wouldn’t say, the price of rim brakes is important here. There are a lot of inexpensive rim brakes that offer pretty good braking. With cantilevers the popular Tektro CR720 comes to mind. You can also get a lot of vintage cantis almost for free – many will offer braking as powerful as very expensive cantilevers like the Rene Herses at the other end of the spectrum.

    • I meant to refer to long-reach sidepull and dual pivot brakes. Most of them are not very good. However, my experience with the Tektros was disappointing: There is so much play in the pivots that the brake pads toe out during hard braking, exacerbating what is always an issue with cantis due to fork blade twist.

    • marmotte27 says:

      Went from the Tektros to Rene Herse. No comparison on braking power. That’s worth every (one of the many) cent(s).

  3. Rick Harden says:

    To me, the most interesting aspect of disc brakes is the ability to run multiple wheel sizes or material on the same bike without changing calipers or pads.

    • This is a common selling point for disc brakes, but I don’t know anybody who does this. Do you? I guess you could have a 700c skinny tire wheelset for road rides and a 650b wide tire wheelset for all-road rides, but I bet most people just have different bikes for different applications.

      As a bike mechanic for the past five years, I’ve never worked on a customer’s bike with two wheelsets of different sizes. Racers often have two wheelsets for training and racing, but they’re the same size. The disc brake wheelsets are usually more work to prevent rotors from rubbing the pads when swapping between wheels.

      • JanHeine's Cousin says:

        I do that with a surly pugsley. 26×4 wheelset and 29×3 wheelset. Can be swapped out in a minute.

      • Mitch Harris says:

        I built two wheelsets (584 and 559) for a Crust Romanceur partly because I wanted to set up a bike for Rat Trap Pass EL tires but wasn’t sure I’d prefer riding them all the time. I knew I could easily change the bike to Babyshoe Pass tires if I didn’t prefer riding it all the time with RTPs. So the value of switching wheel sizes isn’t only for someone will want to switch frequently or routinely, but also for someone who prefers not to decide permanently what rim size a new bike will use. Having ridden I lot of miles both on RTPs and BSPs on that bike, I tried Switch Back Hill EL and have tended to prefer those most and have ridden them longest. Being able to switch back to RTPs if I want is an advantage on this bike, even if it’s just for variety and the novelty of riding a familiar bike with a different kind of tire. Since I built that bike, Compass introduced the Naches Pass which could have offered similar variety compared to the RTPs as BSPs do. But the Naches Pass have a very different overall wheel diameter, and I find that matters to me too, as well as tire width. So for me, being able to vary wheel diameter along with tire width is in the disc brake advantage category.

        By the way, I didn’t choose a disc allroad bike for this wheel size versatility advantage, but instead for what Jan lists above as an mtb advantage: long rough dirt road canyon descents where less hand pressure has the same allroad bike advantage that it does for mtb descents. Descending on dry pavement in my experience, offers no disc advantage for compared to a good rim brake, comparing like to like on the same tires. Maybe there is also a hand pressure reduction advantage for discs on very long pavement descents, but I only begin to notice the advantage on long rough dusty dirt road descents where dust on rim braking services can degrade rim brake performance the way water and mud can.

      • E K says:

        I didn’t expect to, but ended up doing just that – 700×35 for rando rides, with 650×49 for forest road wandering. They even fit under the same set of 27.5 Cascadia ALX fenders.

  4. Correct me if I’m wrong, please, but I think there is another disadvantage to rim brakes that is worth mentioning. As I understand it, putting the braking heat into the rims (e.g. on a long descent) is going to increase the tire pressure — and, if you’re running high pressure or the tire’s range is narrow, could risk a tire blowout / blowing off the rim. Anecdotally someone running the BJP tires tubeless experienced a blowout on a long descent with rim brakes, suggesting that this is probably a real consideration that deserves to be mentioned.

    I can’t offer quantified information on spoke fatigue due to disc brakes, but I certainly agree that disc brakes require sturdier wheels. That said, I’ve ridden 28/28h wheels well above 20,000 miles without any spokes breaking. (I don’t usually run my wheels that long, as I’m always looking for an excuse to build a new set, but that was a trusty commuter wheelset that I particularly liked. Eventually I upgraded to new axle combo and 11sp so sold those wheels — presumably they’re still working well.)

    • You are right, heat dissipation is an issue during long braking. It’s not the air pressure, but the rubber can actually melt. The molten rubber lubricates the tire bead, which then can climb over the rim wall.

      With disc brakes, you eliminate that problem, but you the rotors are smaller, so there is less surface to dissipate the heat. Disc rotors can get extremely hot, which can lead to serious brake fade during long braking.

      • Andy says:

        Check out the recent post on the “beyond the press” youtube channel – they put a bike disc brake on a spinning lathe and brake full force to find out what happens. It’s probably much more power than possible to experience while riding a bike!

      • Gugie says:

        Years ago, on a long tandem descent I blew out both tires. The root cause was the rim strip melted.

        You’re right, Jan, if you do the physics and math, temperature increase, especially on wider tires doesn’t increase the air pressure as much as many think.

      • Johan Brox says:

        I, too, have melted an inner tube on my tandem on a long descent. This was a cheap gas-pipe tandem with terrible centre-pull brakes and an at the time inoperable Atom drag-brake (hence the rear tube melting from rim braking). It made for exciting rides!

        But at the same time, I have rarely seen touring tandems equipped with hydraulic disc brakes, or disc brakes of any kind for that matter, except as a mechanical drag brake. I suspect that the massive tire grip, weight and speed of a loaded tandem riding on tarmac would potentially make the hydraulic fluids reach a boiling point, and hence brake fade (you would in effect be squeezing a highly-compressible gas instead of a liquid).

        My greatest wish is one day ordering a custom, “proper” tandem for me an my wife. Due to above considerations, it would feature Rene Herse cantilevers or brazed-on centre-pulls, unless a knowledgable builder would convince me otherwise. I am however unsure on how to solve the drag brake.

  5. brian says:

    To many of us this is common sense, and has been for a long time, and my head is starting to ache from beating it against the proverbial wall, after years of explaining exactly this to clients while “the industry” continues to push discs into ubiquity. I’m not anti-disc, and they certainly have their appropriate applications with bicycles, but the push that discs “are superior” as a blanket statement is nonsense.
    Thank you for writing it all out in a way that covers [nearly] all the bases around the issue, but also such that anyone can acquire a balanced understanding of the points from both sides.

    • Andy says:

      “The industry” does a good job at making it sound like all upgrades are necessary and related too: You need disc brakes! But wait, those are heavy so upgrade to these carbon rims and fork. But wait, these are safer if you upgrade to through axles! But wait, the mechanical version isn’t strong enough, so get this hydro set. You can’t possibly service this yourself, so come back and we’ll adjust it for a fee… etc.

      Just like how I don’t need to buy a Ford F150 to tow the boat I don’t own up the hill I don’t live on, I don’t feel a need for disc brakes in the conditions I ride either (rarely over 25mph, very rarely on mountainous descents).

    • Virginia says:

      What is this monolithic “industry”? Frankly, everyone champions his/her interests, often at the expense of others to be sure.

      For what it’s worth, the “industry” pushed to resurrect an old standard ETRTO 584 “650B” (aided by industry “iconoclasts” Pacenti and Heine, cynically IMO though Heine does have a a good alibi with the French constructeurs bit). ETRTO 571 “650C” and increasingly ETRTO 559 “26er” rims and high-end tyres are vanishing.

      In the MTB and touring realm, women and smaller riders are suffering for this.

      • Virginia says:

        Actually, I dispatched that a bit too quickly; Heine does redeem himself by offering the 32-559 Elk Pass, which is an excellent tyre.

        However, the larger picture of what 650B has wrought upon “26er” still remains rather grim.

      • 26″ was replaced by 29ers years before 650B became popular, but it’s not dead yet. Compass offers no fewer than four 26″ tires…

  6. Paul Martin Lauer says:

    What do you consider a wide tire? Not, hopefully, the new 25mm or 28mm.

    • I think these days, we can safely call anything less than 30 mm ‘narrow.’ I’d say that ‘Wide’ starts in the mid-30s. Anything above 45 mm is ‘ultra-wide’ for road bikes. At least for now. 😉

    • Mike says:

      This is a good question. A “wide” tire depends often on one’s perspective. I’m used to MTBs, and on my “daily driver”, I’ve run everything from 1.5 to 2.1 inches wide (38 to 52 mm), so those numbers are what I’d consider narrow and wide. I’ve talked to many friends who ride road bikes and they see 28 mms as positively plush. On the other end of things, if you talk to people who ride fat bikes, anything under 3 inches wide is svelte.

  7. Robert Hunter says:

    I’ve been eagerly awaiting Myth #12, and was very pleasantly surprised to see the title. I have long been somewhat critical of disc brakes, for the same reasons you list in the article. I’d like to add one major limitation that more people than my wife and I must have encountered. To wit, we ride a tandem with disc brakes – it’s our touring bike, and a great one in almost every respect. However, after twice reaching the point of having absolutely no braking force left in the middle of a long downhill run, we are rather nervous of long descents. Once your braking starts to fade there is no way to stop, or even to slow down, without running off the road or riding it out to the bottom.

    P.S. Don’t be tempted to touch a rotor once you’ve finally managed to get off the bike!

    • Andy says:

      I’ve heard of tandems relying on a drum brake (often on a bar-end shifter) to help reduce the load on the primary brakes. On long descents, I also tend to alternate which brake gets more force every couple seconds, just to give a brief moment to cool down.

    • brian jenks says:

      I wish to know more about details of your tandem discs, and your experience losing power on long descents. Jan, we know you have a lot of experience with tandems over challenging terrain, and perhaps you can elaborate on the options and effects in a more comprehensive article.
      My wife and I are tandem riders ourselves, and have spent years custom fitting, designing, and outfitting tandems for customers, but this still seems an unresolved problem. Only twice in the past 20 years have we “lost” stopping power in our tandem’s rim brakes due to heat on long descents, and we did not have an auxiliary brake at the time. Once once in SoCal and once (last fall) was in Israel, and it took all the strength remaining in my hands to bring the bike to a stop so the wheels could cool down. Braking technique counts for a lot, but there are conditions when more is required.
      Although I still prefer rim brakes on my own tandems, I have contended in recent years that a rear disc makes a superior auxiliary, and want to learn more about whether this view needs further adjustment.

      • The secret on tandems is to let the bike roll between corners, so most of the energy from the loss of altitude is dissipated as air resistance. Then brake hard for the corners, before letting the bike roll again. That way, even twisty descents are no problem. Gravel is a different matter, where braking hard isn’t an option, and you probably want a non-rim brake.

        The almost total brake fade on discs seems to be due to the pads. I now have Shimano pads on my Firefly, and when following other traffic down Seattle’s steep streets, I’ve experienced almost total brake fade myself. The original TRP pads seemed to be more fade-resistant, but they wore like butter. Still looking for a disc brake pad that offers satisfactory performance all-around.

      • brian jenks says:

        Your secret to braking on long descents with tandems assumes there are turns available. Twisty descents are the easy ones, indeed using the technique you describe. In both instances of our brake failures, they were straight shots (opposites sides of the world too), and the second entered an urban area with intersections and traffic lights, a very long 6% downhill street lined with tall curbs, sidewalks, parked vehicles, limestone walls, and iron gates. Air temps were roughly 100F, and pavement temps were… hot.

      • Traffic is always tricky, as you have to go slower than you’d like otherwise. As you say, my brake failures with discs were in similar situations – following slower traffic that required continuous braking that overheated the brakes. Still, I was surprised that the mainstay pad from the biggest maker, Shimano, didn’t have enough fade resistance to make it down a moderately steep hill in Seattle.

      • Conrad says:

        The only place I have ever melted a tube with a rim brake is descending Bells mountain trail. Its a 2 mile steep descent and in order to not take out hikers you have to brake the whole way. I have done this same descent numerous times on a hardtail mountain bike with Avid BB7 discs / Avid pads. No fade, no excessive wear. In fact I havent worn the pads out yet. I completely agree with everything you are saying about brakes, and a suspension fork is the only place I have a disc brake on any of my bikes, but the Avid BB7 has worked really well for me.

      • I’ve heard good things about the mtb version of the BB7. The road version at first had some issues – mostly insufficient power – but when we tested a bike with the BB7S a few years back, it seemed to brake fine. Perhaps I’ll try those next on my Firefly.

      • We have ridden both, a nice, disc equipped Lapierre and an old yet to be restored Routens equipped with 2x Mafac Racer plus 1x Maxi-Car drum brake through the mountains. I preferred the Routens, as I was afraid of failure with two identical disc brake calipers, and discs running extremely hot. The Mafacs on a twin lever are fine for control in the turns, while the large drum is efficient in taking excessive heat load yet light on the lever.

    • Nathan Grill says:

      What size rotors are you using on a tandem? I would hope at least 180mm on the front? are you using shimano icetech rotors and pads?

      • Mark V says:

        unlike motorcycles or single bikes, the rear brake of a tandem is more important because the center-of-gravity of a tandem is relatively low compared to the wheelbase. Thus the rear wheel doesn’t unload under hard braking like a single bike; indeed the front tyre would likely skid (or the fork would snap) before the rear wheel could pivot up on a nose wheelie. Santana equips their tandems to accept their in-house 254mm rotor and a mechanical disc caliper, the later to probably avoid the risk of boiling fluid on a long descent. the underlying problem with disc brakes on tandems is that the best disc systems on the market were optimized for single bikes and invariably are inadequate for the heat management issues of tandems on long descents.

      • Beau says:

        Working at a tandem shop, I’ve actually seen IceTech rotors that failed from excess heat. The aluminum in the sandwich melts and the whole rotor goes to hell. IceTech seems to be great for mountain bikes, but tandems are a wholly different animal.

    • Andy Stow says:

      Jan’s advice is sound. Let the air dissipate most of your energy. Sit up and extend your knees and elbows out if you want to save your brakes a bit.

      I did the math a while back using a basic physics model, and the worst possible speed to descend at is around 60% of your terminal speed (the speed you would achieve without braking.) Unfortunately, I’m guessing that’s a pretty common speed to comfortably go. See the writeup I did here:

      https://www.crazyguyonabike.com/forum/board/message/?o=1mr&thread_id=728230&page=1&nested=0&v=2D

      As an example, a 200 lb / 90 kg (rider + bike + load) descending a 10% grade has a terminal speed of about 35 MPH (55 km/h.) If he brakes to hold a speed of 35*0.6 = 21 MPH (34 km/h) his brakes will need to continuously dissipate over 1000 watts! A faster or slower speed will be better for his brakes.

      I’m happy to share my Google sheet if anyone is interested.

  8. DaveS says:

    I find it interesting that the bicycle industry is OK with the extra weight of disc brakes, but wasn’t OK with beefier rim calipers (which would have been heavier, but not as much as adding disc brakes).

    • Jacob Musha says:

      The mainstream bicycle industry is fine with anything they can market as “new and improved” in order to sell you a new bike. Whether either of those actually apply is irrelevant.

  9. Grant Diamond says:

    Jan, I encourage you to find a test bike with dual piston mechanicals and compressionless housing. Much better feel at the lever, powerful enough to throw me off the bike with my butt behind the seat, and maintenance is significantly easier than both rim brakes and hydraulic discs.

    • Phil says:

      he’s using TRPs on his firefly. If I recall, they use dual piston design. I would also assume he’s using compressionless housing, as thats pretty much the standard cables for discs.

    • Sylvain P says:

      TRP spyre changed the game haha

  10. Roberto says:

    Agree. Tektro R559 rim calipers clears without problems your Compass 42-700 (actually 44mm), and well adjusted they have almost the same power than a good pair of hydro disc. And they are lighter and simpler, and usually quieter. Doesn’t like water, though.
    But customers are asking for disc brakes all the time, even for urban bikes, since industry marketing is making its job.

    • My experience with Tektro’s calipers has been less than satisfactory. The fact that they “don’t like water” shows that they lack the brake power needed to cut through the water film on the rim. But just because Tektro’s brakes are sub-optimal doesn’t mean that rim brakes inherently offer poor performance.

      • Mark V says:

        On one bike I swap between SRAM Red calipers/700C wheels and Tektro R559 calipers/650B. In rain or dry, the SRAM Red calipers outperform the Tektro in every aspect…except tyre clearance. I have another bike with SRAM Red hydraulic disc brakes, which beat the pants off the Tektro…absolutely no contest.

  11. Conrad says:

    That Hirose looks wonderful. Would that U brake be able to clear a Rat Trap?

    • Good question. It’s interesting that in order to improve cantilevers, Shimano (?) came up with a beefed-up centerpull brake. It didn’t catch on mostly because of the mounting location under the bottom bracket (where it got caked with mud), but C. S. Hirose uses them in more conventional locations on his tandems. I have no idea how much tire clearance they offer.

      • Conrad says:

        I did a drop bar conversion on a vintage Rodriguez mountain bike with an XT U brake on the chainstays and wide profile cantis on the front. The U brake clears Rat Traps just fine on the back. I sort of wish the bike had the same brake on the front but I’m not sure it would work.

    • Jan G says:

      I run that setup and can confirm that it does, with about 1 cm clearance. That brake was designed to fit that size casing, plus big knobs.

    • Mike says:

      My bike has vintage U brakes installed on the rear, old-school cantilevers on the front. Thankfully they installed them on the seat stays, not the chainstays, on my bike, so I never had the caked-on-mud problem. The old u-brakes can easily clear a Rat Trap Pass; an RTP with fenders is a little dicey, but doable.

    • Murray Watson says:

      I have an old Kona with a Shimano rear U brake on the seat stays, it easily clears a Rat Trap Pass (possibly also fenders)

    • Wilson Wilson says:

      Yes. They came stock on many Scott and relabeled MTB in the proper location. Some frames fit 2.125 XC tires.

  12. Dr J says:

    The current trend to use wider tires in road bikes should stimulate a development of appropriate caliper brakes. Unfortunately, that didn’t happen and industry simply switched to discs. I would love to have a road bike with 32mm Compass tires that wouldn’t require disc brakes.

  13. Simon C says:

    Absolutely agree that disc brakes are no better than rim brakes in most circumstances, certainly there is no more power or control in ideal circumstances. If you do a lot of wet weather riding though then disc brakes are absolutely worth considering.

    My all-weather commuting bike has disc brakes on it, and I wouldn’t change them for anything, as they outperform all rim brakes I’ve used in adverse conditions. Weather in the UK can be so bad in autumn/winter that rim brakes become utterly inconsistent in how they respond to a lever pull, whereas disc brakes behave the same every time. Forget all other considerations, for me that predictability is why my next bike will also have disc brakes.

  14. PaulS says:

    Thanks for the balanced critique. In my experience, good quality, modern dual pivot rim brakes on a road bike are just as good (for power and modulation) as any hydraulic brake; and they make vintage sidepulls look ridiculous. On mechanical disks, I have a very good set of TRP Spyres on a road bike; they have great modulation and adequate stopping power (with 160 mm rotors) and are extremely smooth and quiet, none of the judder you get with a lot of disk brakes.

  15. Larry Naylor says:

    While I agree that rim brakes are pretty fantastic on skinny tire bikes, I do not believe the nose wheelie is a valid test of braking power. As stated, most brakes work by using friction to create heat which is then dissipated. My argument is that the nose wheelie is a function of leverage converting forward momentum into lifting power. Since the disc brake is located closer to the fulcrum point it has less leverage, while a rim brake being farther away has a longer lever arm, and therefore a much larger mechanical advantage. This extra leverage, is what allows rim brakes to lift the rider into a most satisfying nose wheelieing position.

    • Lifting the rear wheel is simply a function of the bike’s geometry and weight distribution, forward speed and braking power. Where that power is applied (at the top of the wheel by a rim brake, in the center by a disc brake, or at the bottom by hitting a large rock) makes no difference – you go over the bars unless you can reduce the brake power.

      You are right about the extra leverage of a larger disc rotor, which is why smaller disc rotors require more clamping force to achieve the same brake power. For example, I’ve found 160 mm rotors working just fine with hydraulic disc brakes, but not offering sufficient braking power with mechanical discs. A rim is the largest rotor you can fit on a wheel, but the clamping force of rim brakes also is lower – it all comes out to the same if the brakes are well-designed.

  16. Jason Miles says:

    I believe Disc brakes have already overtaken rim brakes in new bike sales, both on road and mtb bikes. In the long term I think this means availability of rim brake parts will start to become an issue. Component and bike manufacturers will start to dedicate the latest technology only towards Disc brakes.

    One issue I ran into is finding a rim brake compatible, tubeless, 26″ rims. I love my Rat trap pass tires and if I were buying a new bike I think I would go with disc for this reason alone. I ended up with some very inexpensive Stan’s ZTR 355 rims purchased on Ebay. The only other rims I could find in this combination are the Velocity A23s and Cliffhangers.

    • Joe says:

      “In the long term I think this means availability of rim brake parts will start to become an issue. Component and bike manufacturers will start to dedicate the latest technology only towards Disc brakes.”

      It’s possible. But can you imaging the marketing you could do with the idea of “For the highest levels of performance we use the *rim as the rotor* with our revolutionary new brake. Just as strong, just as sensitive, and a whole lot lighter with a better ride in the fork too”.

      I think the marketing department could work with that once we are all on disk brakes 😉

    • Josh says:

      There’s a gigantic install base of rim brakes bikes (almost literally the entire history of bicycles until this moment). It will be at least a century until it becomes difficult to find rim brake parts.

      As for 26″ tubeless rim-brake rims, go for the Alex Adventure 2. Probably one of the best all around bang-for-the-buck rims on the market.

      • marmotte27 says:

        Only the bikes you’re talking about will very quickly cease to be considerd high end bikes (just consider pro level road bikes from say five years ago, they’re totally outdated these days – if you believe bike makers). And so they stop making high end parts for them. Of course I can by a cheap Chinese freewheel anywhere. But that’s not what I’d want on my seventies high end Motobécane.

  17. George Recker says:

    Thanks to my muscle memory on old style brakes, I over grabbed a handful of disc front brake on a gravel decent . Now six weeks latter I’m almost off my walker, and on to a cane. Broken femur!! No Divide ride this year. Disc brakes are too grabby for me. I wish I’d followed my intuition and changed them out to cantys. Live an learn, follow your instincts.

    • I am sorry to hear about your accident. Modulation can be tough with disc brakes. Make the rotor very large, and you get a lot of power, but also very grabby brakes. Make the rotor too small, and you can’t really stop on the road. Some of this may be inherent to moving the braking from the rim to the wheel’s center – where you may not get quite as clear feedback on how much traction you have in reserve – and some of it may be improved by better brake design.

    • Peter Chesworth says:

      Welcome to the Broken Femur Club George. 7 months along, cycling is fine and has been excellent therapy since week 10. Walking still limpy at the end of the day but slowly imroving. Treat it as a 12 month project.

  18. VincentB says:

    I cycle all year, often in bad weather. Problem with rim brakes is that the rims wear very quickly. On one of my bikes, with hydraulic rim brakes, the rim of the rear wheel could wear unusable in only 5000-6000 km. Disc brakes to the rescue 🙂

  19. Rick Thompson says:

    You don’t mention pad material for rim brakes, but my impression is that newer pad materials have improved rim brake performance. My road bike with sidepulls and fairly new pads was stopping OK, but recently installed Kool Stops are better dry and wet.

  20. SS says:

    I think everyone should immediately convert to disk brakes and then sell me cheap your rim brake carbon Lightweights and Zipps.

  21. Bob Vineyard says:

    I’ve just begun using disc brakes, with 203mm rotor up front, 180mm in the rear. I’ve not experienced any brake fade (yet!) but I will say, compared to rim brakes on long descents, the small force required to actuate a hydaulic disc significantly reduces hand fatigue. (I’m riding a Jones setup for the road, so using mountain levers.)

    • Mountain bike disc brakes are a totally different matter. Just the size of the rotors is much larger, even though you can’t use much brake force on loose ground, where tire traction limits your braking. It makes no sense that road bikes often are equipped with tiny 140 mm rotors, when they actually could (and should) brake much harder than mountain bikes.

  22. scott g. says:

    The real reasons for Disc brakes…
    Disc brakes make carbon clincher rims safe to use on long or wet descents.
    Hydraulic brake lines are easier to route in Aero & TT bikes.
    Hydraulic master cylinders take up a lot of space in Brifters, hence
    electronic shifting. Also electronic shifting, wired or wireless is easier to install
    in Aero and TT bikes. (semi-seriously)

  23. Disc brakes DO WORK BETTER than rim brakes and offer additional advantages like e.g. ability to fit different wheels size to the same frame and elimination of a rim wear issue.
    At the same time however I agree that vast majority of road cyclists absolutely DON’T need them and they make modern bikes more complex and expensive than they need to be.

    Regarding mechanical disc brakes, there is one that works – Paul Klamper.

  24. Sylvain P says:

    The trend in road race frames of direct-mount calipers seems to be a good one in terms of optimising weight savings and brake modulation. Anyone making a DM brake for wide tires??
    (other than U-brakes!)

  25. Phil Houck says:

    There are so many unanswered questions and such severe heat fade issues with disc that I think I’ll stay with rim (calipers and cantilevers) for any mountain riding I do. Questions about what happens with brake rotors encountering frequent heat and cool cycles also concern me.

  26. Peter Chesworth says:

    Nice provative piece. Hydraulic actuation seems to be a significant improvement over cables. Magura makes a hydraulic rim brake. I wish they would make it with levers suitable for drop bars, as an alternative to cantis.

    • What I find interesting is that for a disc, hydraulic actuation makes the brake simpler (just push two pads together), while on a rim brake, it complicates the brake. I predict that mechanical disc brakes soon will be gone, just like they are on cars and (I believe) motorbikes. The screw mechanism used on most mechanical discs is not an elegant solution for transmitting the pulling force of the brake cable into a clamping force of the disc rotor.

      • Peter Chesworth says:

        Indeed, although the Paul Klamper is a piece of art. The potential advantage of hydraulic “cantis” are firstly, removing the problem of fork shudder caused by steerer tube flex ion and resonance (a fork mounted brake hanger won’t fit if you have something like a Nitto M12 front rack already using the hole) and secondly, removing the messing around with cable hanger height. It is a shame that these are available for flat bars but not for drops.

      • The fork judder is mostly a problem with forks where the steerer is too flexible and the blades are too stiff. When you use a flexible blade like the Kaisei TOEI Special, you don’t get fork judder even with cantis. Straddle hanger height only matters on low-profile cantis, and those are pretty much gone for that reason. With wide-profile cantis, straddle cable has almost no effect on mechanical advantage.

  27. Mark Atwell says:

    Rim brakes can be really useless if you break a spoke and cannot fix the wobble. A disc just soldiers on.

  28. Todd Teachout says:

    My experience with disc brakes (at least with TPR HyRD hydraulic/mechanicals brakes) is that break pad effectiveness goes away after about 1000 miles.

    Up to that point the brakes modulate well and stop nicely. After 1000 miles modulation goes away rapidly and stopping quickly requires unacceptably long distances to slow down. This seems odd as the pads themselves seem to have a lot of material but it somehow gets contaminated and cannot be cleaned to restore the abrasiveness/grip power.

    Because of the relatively short range of disc brake pads, I’m using my disc brake bike less and less.

  29. Going back to Jan’s comment, “Disc brakes transmit all the braking forces through the wheel and fork legs, so both must be stronger”, there’s another very important issue with fork stiffness: when all the braking force is transferred into one blade of the fork, any “springy” fork will deflect and seriously affect handling because only one blade deflects. Motorcycles use dual calipers for this reason, I believe.

    • I experienced that on an early allroad bike with a Wound Up carbon fork. The gravel descent from Naches Pass has long straights interrupted by sharp turns. Braking hard, the bike steered to the right. I quickly learned to compensate for this by steering to the left every time I braked. (Not sure what I exactly did with countersteering and all, but it actually was intuitive enough that it only bothered me slightly.)

    • John Collier says:

      Motorcycles use dual discs at times for a variety of reasons, including the one we are most familiar with, fashion. Racers vary the size of their discs to the circuits required braking (larger discs provide more surface area for heat dissipation). However, larger discs weigh more and affect turn in speed so they fit the smallest rotors that get the job done. On really “brakey” circuits, they use carbon discs for their ability to handle high heat. You have to be careful though as materials to handle high heat loads don’t work when cool. This leads to disc brake set-ups that use covers to contain heat!

      Back to dual discs, it is primarily about braking feel. When discs first came out, pads were hard, levers were long and lever forces high. While brake power/lever force ratios were linear, the high lever forces meant there was very little “feel”. It was very hard to balance on the point of incipient front wheel lock. With dual discs, softer inorganic pads and multiple piston calipers, lever forces are low, very low: two finger levers are the norm. This along with super stiff forks, gives an amazing “feel”. You can literally feel the tire’s carcass deflecting and the “squirming” that signals incipient front wheel lock. Watch an upper echelon, large capacity motorcycle race and you’ll see them come into corners with their rear wheels off the ground and their fronts sliding around as they balance the braking force right on the point of front wheel lock.

      On the road such antics are not encouraged nor desirable. This is where fashion and magazine writer-ease comes into play. There are lots of sensible bikes with single disc brakes that work very well, provide good feel and weigh less.

  30. Jon Blum says:

    Heat can be a problem with either kind of brake, and this proved troublesome a few years ago in a very hot race in the Middle East. A descent was neutralized, and the riders had to brake all the way down (not what pros normally due). One team had multiple tire failures, reportedly due to tubular glue melting from the heat, resulting in valve failures as the tires slid along the rims. Another reminder that heat buildup is a bigger problem if you descend slowly with a lot of braking.

    The ProTour teams seem to be transitioning to discs. That is probably mostly marketing, but the extra weight and stiff forks are really a non-issue for them, given the UCI weight limit and use of carbon forks. Perhaps there is a legitimate advantage for them because of shortcomings of rim brakes on carbon rims, which have completely supplanted aluminum in the pro peloton. I don’t know if brake pads have improved to the point where caliper brakes work really well on carbon rims, which was a big problem in the early days of that technology.

    I’m not advocating disc brakes, as I am happy with my rim brakes and have not even tried discs.

    • Francisco says:

      It’s funny how people say every bike in the professional peloton would be below the UCI weight limit if only they could, but take a look at actual bike weights and they are typically 7 ~ 7.5 kg for the brawnier professionals.

    • Ian says:

      Brakes are definitely marketing at the World Tour (ProTour ended 8 years ago). They are racing, they don’t stop. They only slow down, and as little as possible.

  31. Tony Guttmann says:

    I am an older (73 yrs) rider, and not a super-confident descender. I found that on my high-end Ti road bike with Campag. Super Record rim brakes when going down long, steep descents, my hands would become quite fatigued from applying the brakes to control the speed to a level that i felt comfortable (30-40kph). I have switched to another Ti-framed road bike with Sram disc brakes and couldn’t be happier. The force required to restrain the bike to the speeds I’m comfortable with is much lower, and so I’m enjoying riding much more.

  32. John Duval says:

    What is good about disk brakes isn’t the disks, it is the hydraulics. I put Magura hydraulic cantilever rim brakes on a tandem bike and found them much better than disks. Power was plenty for a 200kilo load and one finger. It took little lever travel, but the pads easily had 5mm of clearance from the rim. If I can find compatible road levers, I may build my next bike with them, though they are very unattractive to look at.

  33. Owen says:

    Relative to discs, rim brakes are easier to design and manufacture and I believe there will always be small companies like Compass and Paul who can economize to scale and supply this market. What I’m more concerned about long term are rim-brake compatible rims, particularly of the tubeless variety. Jan correct me if I’m wrong, but isn’t rim tooling and manufacturing a more complicated and expensive undertaking?

    I’m really enjoying this series and evidence + experience you present along with each Myth, glad to hear you’re keeping it going!

    • Rims aren’t that difficult to make, so I don’t think it will be a problem in the future. There are so many bikes that are ridden a lot and wear out their rims…

      • Thomas Smith says:

        Jan–I don’t think the potential supply problem with rim-brake-compatible rims relates to the degree of difficulty in their construction, but rather to the demand perceived by the manufacturers. Although I can see where the demand for 700c and 26″ rims will remain strong for some time, I think we’re already at a point where good-quality rim-brake-compatible 650b rims are becoming rare.

      • Agree, demand is the problem, but these days, even small-scale manufacture is possible. It costs a bit more, but you no longer need a market for 10,000+ units a year to make a product happen.

        As to rims for different wheel sizes, there are far more good 650B rims than 26″ ones. At Compass, we sell the Pacenti and the HED Belgium Plus, both excellent rim-brake 650B rims. For 26″, it’s much harder to find a good rim-brake rim.

      • Conrad says:

        The Velocity aeroheat is wonderful and reasonably priced. I will throw a tantrum if they discontinue it!

      • Do you have problems with them cracking? We’ve had too many Velocity rims of all types crack around the spoke holes with relatively low mileages (<5000) to have much confidence in the brand.

  34. KaiS says:

    well although a well written and comprehensive article, it only gives fractions of evidence for its thesis. you are usually more clear-cut than this, Jan;) are you not so sure of this one?

    rather you get the impression it is the other way around, and all pro and con aspects considered probably this is closer to the truth. in spite of also disc brakes having their shortcomings. what i dislike most about rim brakes is not their efficiency, but the fact that they destroy my nice rims. actually just one substantial decent in rainy dusty conditions can do enough harm having to replace them.

    with uci now tolerating disc brakes also in sanctioned races its just a matter of time before they have taken over entirely.

    • The world is rarely black and white. In many cases, the answer is “It depends.” Disc brakes have their place, but for most of my riding, I prefer rim brakes. Also, rim brakes have been perfected for many years – the Compass centerpull brakes are based on decades of experience with centerpulls – while discs clearly are still in their infancy. They are getting better, but they’ve got a lot of catching up to do.

  35. Micha says:

    ” If you’ve ever ridden a bike with drum brakes across hilly terrain, you’ll know how dreadful they tend to be: …. That is why they never became popular, especially since the bicycle’s rim provides a convenient brake ….”

    Never became popular? Maybe not for road bikes or MTB’s, but most Dutch city bikes that do not have a coaster brake have drum brakes, and if the venerable Sheldon Brown is to believed a lot of Japanese city bikes as well.

    For Dutch (city bike) situation (or at least Western Dutch) the drum brake is quite ideal: performance is unaffected by the weather, low maintenance (as Dutch city bikes suffer from a benign neglect) and steady performance by low- to medium speed. As most of the Netherlands is quite flat the whole downhill/descent situation does not come into play.

    All-road and MTB are a different situation altogether of course.

    • You are right, coaster brakes on European city bikes are drum brakes. (The Japanese city bikes use band brakes for the most part, which are even less effective.) At the low speeds and flat terrain where these bikes are used, there isn’t much need for great braking performance…

    • DaveS says:

      Micha, my experience with drum brakes in mountainous terrain is different. Our previous tandem had an Akai drag (drum) brake along with 2 rim V-brakes. On long, steep mountain descents where speed needed to be controlled, I had more confidence with this setup than with our new tandem that has 2 disc brakes with 8″ rotors in the same conditions. Of course the Akai drum brake is a good size chuck of aluminum which probably weighed pounds more than the drum brakes you used.

  36. fnardone says:

    I was a disc convert when I had a 26″ MTB with 180mm hydraulics. Sold that and got 2 different road-ish bikes with 160mm spyre and was disappointed both times; even with compressionless cables they have a very spongy action and failry average stopping power. It baffles me that they do not at least spec them with larger rotors.
    I am not on board the “too grabby” train thou: I find discs to be more precise and immediate if anything. Maybe it’s just a case of getting used to that.
    Fun fact: I once converted from drop to butterfly bar and braking power inceased cosiderably.

    • One issue on a bike without suspension is that you bounce around a bit when riding fast on rough gravel. With the light lever forces, the makes it hard to squeeze the brake levers consistently as you brake from high speed. Hit a bump, squeeze the levers a bit harder, lock up the front wheel…

      • John Duval says:

        “Grabby” goes both ways. With motor vehicles, the brake is sized and power boosted to match the vehicle. But on bicycles, one size fits all, which means few work adaquately for me. Ideally, you would be able to tune them to your weight and riding conditions. Unfortunately, with good brakes, if you need more power, you can’t simply add mechanical advantage; the lever will hit the bars. But with poor brakes, they have only one level of braking force, no matter how hard you pull on them.

      • fnardone says:

        Well, I can only say that I ride on gravel with a rigid bike and I have never encountered that problem. Discs are more linear in their response, if you grab at them as if they where rims you are going to have problems.

      • The grabbiness is real. You can experience it especially at low speed. I believe all brakes experience this, when the friction of sliding becomes friction of sticking (to avoid more technical terms). Disc rotors turn at lower linear speeds than rims (due to their smaller diameter), so the speed at which the disc becomes really grabby is higher than with rim brakes. Rims brakes grab only at speeds so low that you have a hard time balancing the bike anyhow.

    • Frank says:

      Hi.
      I know that Jan isn’t a fan either, but I’ve had good results with the Spyres. I live in a hilly place (Hobart), and my bike and I weigh about 90kg together. I find they stop well, modulate nicely and are easy to adjust. I’m confident descending the mountain as well as playing in traffic to get to work. I run them with …
      jagwire compressionless housing, 160 ice tech rotors, swiss stop sintered pads (the first set of pads lasted maybe 7500km?)

      Sometimes … the dual piston action of the spyres is sticky and needs a bit of ‘convincing’. I found this short youtube video … https://www.youtube.com/watch?v=CDYgQpmKiBs
      and it made all the difference (at ~ 50 seconds she adjusts the brake and then it functions as it should).

      Best. Frank

  37. samuel thompson says:

    I’m not really sure where the “disc brakes tend to grab” comment comes from. I have been running hydraulic discs on several road and cross bikes for several years and i have never experienced this. Hydraulic discs don’t require near the force that rim brakes do and are very easily modulated. If you come from rim brakes maybe you just haven’t adapted to how smoothly, evenly and consistently the disc brakes work. Rim brakes will require different efforts front and rear because of the cable stretch. The cables may not be perfect and have some drag.
    I think a hydraulic brake equipped bike with electronic shifting is the pinnacle of road bike performance.

  38. Stuart Fogg says:

    Regarding disc pads, I’ve been very happy with SwissStop e-bike pads. In pad life, fade resistance, and lever force they’re better than the OE Shimano and TRP pads.

    I’m now using TRP HY/RD brakes with 180/160 rotors and almost compressionless aluminum-bead cable housing. I’m getting most of the advantages of hydraulics and I can use any levers I want (currently bar-end levers in a TT bar). For my purposes the only downside is the weight of the rotors.

  39. Virginia says:

    “Myth 12: Disc Brakes Work Better Than Rim Brakes”

    No, they do not for some of the reasons cited in the article (but a much better explanation is offered by a real engineer Jobst Brandt online).

    However, the *ROAD* bike I am now building to replace my old one is definitely a disc brake bike. WHY???

    Well, I am 4′ 11″. To achieve proper trail / wheelbase with reasonable fork offset, caster angle and no toe overlap, I have to use 650C wheels. No, 650B will not work (and I haven’t found any 23-25 mm tyres for 650B in any event).

    And because 650C has been become obsolete (mainly because of UCI and industry collusion), the supply of my preferred 650C rim (Mavic CXP-33, 28H) is now limited to the eight I have on-hand (I once had 18) or the occasional auction on Ebay. For the amount I ride, I simply cannot afford to consume rims with caliper brakes any longer.

    Yes, I know about Kool Stop salmon pads – which I use – but the fact remains that if you ride 10K miles annually in moderately hilly terrain with some inclement weather, you will eat rims at an alarming rate.

    So my choice for discs is in no way based on performance but strictly on limited extant resources (no, I’m not bitter).

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