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All of my cycling fellows always told me that it's much more difficult to fully stop a road bike, compared to a mountain bike, because "road brakes just don't work so well" (and perhaps because of skinnier tires).

When I started to ride bikes with road wheels (700x23) and dual-caliper road brakes, quite a few years ago, I noticed my brand new Tiagra brakes were lame compared to even MTB cantilevers, and I ended up replacing the pads by v-brake ones (glad I did).

But I have also noticing the relative danger of "cascading braking" in a tight pack, which can cause severe rear-collisions.

So my question is: are road brakes designed to have less braking power than MTB ones, in order to avoid peloton accidents or whatever? Or is it incidental? Or yet, actually only the lower-end ones don't brake so well?

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    In short, yes - road or caliper brakes are more designed to control the speed of the bike rather than to stop it completely. This is why there is so much emphasis on the "brake modulation" in marketing materials for shimano, sram, campy, etc. – birthofearth Dec 12 '14 at 15:41
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    Note that there is rarely the need for a full "lock the brakes up and skid" stop with a road bike. So the brakes tend to be designed to allow better control over braking. – Daniel R Hicks Dec 12 '14 at 16:46
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    Never had a problem with my road brakes: current Ultegra, and I can still lock up both front and rear at 100kg rider weight. So might be lower end brakes that are not as powerful, and I regularly stop/slow from 80km/h descending mountains. – Andrew Lowe Dec 17 '14 at 23:11
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    Do you mean it's harder to (exert sufficient braking force to) lock the wheels, or takes longer to actually stop? IMO the former is false, unless your brakes are set up badly, and the latter is true and explained by having a smaller contact patch and (as Z. Fechten said) higher speed. – Useless Dec 19 '14 at 11:13
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    When riding on the drops the braking power is much better and usually more than sufficient. (This can cause problems if somebody in front of you is braking hard on the drops and you are riding on the hoods) – Michael Mar 13 '16 at 18:18
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I'm not sure "designed" is the correct word, evolved comes much closer. Current dual caliper brakes actually stop a lot better than previous single caliper sidepulls. There has always been a compromise between weight and braking power. The designers have focused on how light they can make a brake that stops "enough". I don't think there has been any effort to deliberately reduce the performance.

Older centerpull brakes such as the MAFAC Racer actually compare quite well to current dual calipers, but they are much heavier and more complex to install. Designers switched to sidepulls to save weight, but then compromised braking performance.

The problem is that you can only do so much with a rim brake without risking locking up the wheel. You get the most effective braking by stopping just short of the point of locking up the wheel. ( This is called modulation). Given the nature of rim brakes it's very difficult to increase the braking force while still maintaining sufficient modulation. This is the advantage that disk brakes common to MTB provide.

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    There are also materials issues to consider. Carbon wheelsets usually require cork pads that are less effective than regular brake pads so they don't damage the rim. – Deleted User Dec 12 '14 at 17:11
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    Last paragraph is completely incorrect. Prior to disc braked MTB had V brakes which provide significantly better braking force than road bikes, yet were still able to be modulated and control lockup. i.e. It is absolutely nothing to do with discs. – mattnz Dec 12 '14 at 22:41
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    Disk brakes have no advantages over any other brake as far as locking up a wheel goes. Thats a function of your tires and the road surface. – whatsisname Dec 14 '14 at 8:26
  • @whatsisname - No advantages? How about in the pouring rain when rim brakes essentially do not work until you clear the rims of water? How about in wet and freezing conditions? How about better modulation so that you can brake consistently right up to but not over the point of lockup? – Rider_X Mar 10 '16 at 19:23
  • @Rider_X Disc brakes only prevent lock-up insofar as they give you better modulation, which arguably isn't a mechanical advantage. The rest of your comment isn't relevant to wheel lock-up. – Will Vousden Mar 16 '16 at 12:08
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In a comment, you mention that you are using V-brake levers. V-brakes have different mechanical advantage than road brakes and require more cable movement with less force. With levers like this, you can not produce enough force. If you can't use drop bars, switch to levers designed for flat bar road bikes or cantilever brakes.

With decent road brakes, there should be no problem either lifting the rear wheel or locking both wheels. This is the actual limit and there is something wrong with either your equipment or technique if you can't reach it.

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You have to remember speeds are higher for road bikes, and kinetic energy is a function of speed squared. Riding at 15 mph compared to 10 means the brakes have to get rid of more than twice as much energy.

We could get technical and start talking about different wheel diameters and tire weights and all that, but the point is, you have to compare apples to apples. Stopping from the same speed on the same surface, different bike types will have similar braking distances.

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    Only correct if the torque the brakes can exert on each wheel exceeds the static friction of the tire/road surface of the wheel the brake is operating on. Also presumes the operation of the brake is accurate and fast enough to be able to hold the wheels on the point of exceeding static friction. Practically maximum stopping comes from no only being able to lock the wheels, but having the control over the brakes not to. – mattnz Dec 14 '14 at 4:52
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    @mattnz: every respectable brake, rim or disc or other, is capable of locking up the wheels. – whatsisname Dec 14 '14 at 8:29
  • You're right, matriz, but if you understand enough about physics to know that, you know I'm right about speed being a huge factor. By the way, did you know that ABS brakes on new bikes are basically illegal in the US? – Z. Fechten Dec 14 '14 at 18:40
  • Althoug common speeds are higher on road bikes, mountain bikes plus mtb gear wheights significanlty more, thus an mtb has more kinetic energy than a road one, both moving a the same speed. – Jahaziel Mar 10 '16 at 17:21
  • By the way, my current personal descent speed records are almost the same for MTB on dirt and for Road Bike on Pavement. ;) – Jahaziel Mar 10 '16 at 17:23
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No. They are designed to brake as well as possible without being unnecessarily overkill.

The reason why the brakes are a lot less powerful than mountain bike brakes is because they don't require as much force to lock a road bike wheel. That's it. As long as you can lock the wheel, your brakes are powerful enough. You would put the best hydraulic mountain bike brakes on a road bike and it couldn't stop faster. The limiting factor is the grip of the tires. That's because road bike tires have a small contact patch, high air pressure and slick thread. That's all to improve performance moving forward, as road bikes typically don't need performance braking.

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    On slick road surfaces road tires should have similar or even better grip compared to mountain bike tires. – Michael Mar 13 '16 at 18:09
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Your experience differs from mine. I have drop bar bikes with both cantilevers and V-brakes (which are used to clear large tires) and dual pivot side pulls (which manufacturers prefer to use when tire clearance is not a problem, even though there is no particular weight advantage) Using the same shape of brake levers for both, it's the dual pivot brakes that feel the best in my experience.

Here's a question: Are you braking from the hoods, or the drops?

The "aero" lever shape installed on road bikes is a compromise because riders want to hold the bars and access the brakes from different positions. Its fulcrum is on top, and riding "on the hoods" your fingers grip the lever 1-2 inches from the fulcrum, and pull obliquely across the lever.

Because the lever extends down 4 inches, you can get twice as much leverage and finer control by pulling the end of the levers from the drops as you can by pulling from the hoods. I find one or two fingers on the front lever suffices for almost all braking, but only if I am in the drops.

  • Good point on bad mechanical advantage from the hoods. But actually, I am riding a flat bar road bike, so I use V-Brake levers. Anyway, this is a common complaint between fellows with much more experience than me, riding drops and all. – heltonbiker Dec 16 '14 at 11:34
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    @heltonbiker well, that's your problem. Road brakes require different brake levers with more leverage and shorter cable pull. – ojs Mar 9 '16 at 21:00
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The fact a new batch of road bikes (race road bikes at that, not just general purpose road bikes) are now emerging with hydraulic disc brakes, and the UCI has now started paving the way for these types of bikes to enter Grand Tours, would suggest that previous brakes have not been explicitly designed to be less effective. Rather older style road rim brakes actually braking performance was likely considered to be "good enough" with the added benefits of weight reduction and minimal aerodynamic drag and general reliability of the design. Now with major manufacturers producing disc brakes race road bikes it is clear that there is a demand for better braking in road bikes (especially in foul weather conditions - where rim brakes can at time often sub-par braking).

As an aside, road disc brakes have been shown to have higher drag in the real world due to off-angle wind interacting with the rotor and caliper. The increased braking performance was likely viewed as a advantage despite the increased drag in some situations.

If lower braking performance was viewed as necessary for safe group riding (because people are incapable of modulating the brake lever?) then the UCI (which is noted for its slow technology adoption policies) would not have continued to trial disc brakes in professional races. Furthermore, if lower braking performance was a design goal for race road bikes that will be ridden in a peloton, then manufacturers would likely only have only created road bikes with disc brakes aimed at general purpose or "all road" riding.

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From an empirical point of view, I would say YES. Here is my reasoning:

A mountain bike typically has a more "laid back" geometry, which allows the rider to transfer more weight towards the rear tire. This allows to apply greater force to the brakes without going over the bars because:

  1. The rear tire is effective for braking only until weight transfer lifts it and it starts skidding. If your bike geometry puts more weight in the rear tire (proportionally) than another bike, then you bike can be stopped in a shorter distance, for the same speed, surface, (bike+rider) weight, etc. using the rear brake.

  2. The front wheel, is responsible for greater part of the braking action, but then again, if you have proportionally more weight towards the rear, you can apply greater force to the wheel. There is a limit for this though, since putting too little weight on the front tire makes it easier to skid it and loose control.

So, just by changing bike geometry, and assuming normal rider positioning (i.e. not getting out of the saddle towards the rear), the MTB rider can apply greater braking force. Add the psychological factor of feeling that you are less prone to flip over. With this alone, I would argue that an MTB is capable of coming to a stop in a shorter distance, but there is more.

A typical XC mountain bike is heavier than a road bike, so, both being a the same speed, the MTB has more kinetic energy, so to come to a stop it must get rid of a greater amount of energy. But since the MTB is already heavier then there is no problem installing slightly heavier brake systems. Let´s assume then that all that extra weight (in brakes) is exclusively to yield more braking power.

Another aspect is the use mode that MTB brakes receive. For example for DH riding, most of the braking is sharp, hard braking, on planned parts of the course, to the point that intentionally locking the rear wheel to skid it and make a sharp turn is a somewhat common technique. In XC the use is less dramatic, but the general idea is that Mountain bikes, for different disciplines usually have to negotiate technical descents, where it frequently will be necessary to reduce speed as fast as possible.

Road riding on the other hand, needs smooth speed control. I'm not saying that there aren't emergency stops, but they should be rare, and considering that road bikes are built to be lighter, on every part of them where you can shed weight, you should, thus designing an overly capable brake system, at expense of weight is definitely off the table.

From this, I naturally conclude that road brakes offer some minimal braking performance, sacrificing it for the sake of weight savings (And aerodynamic performance).

Putting it all together seems reasonable to think it is easier to stop while riding an MTB than a Road Bike, but to answer the original question, it's not that road brakes are underpowered, MTB brakes are overpowered (when used in the same condition as road ones)*.

From the few times that I have ridden road bikes, I agree that using the levers from the drops yields more braking power and control than riding on the hoods, but no matter if the brakes where top-line or 30 year old Dia Compe, they all felt "spongy" compared to the "solid" feel of a freshly installed v-brake. This "sponginess" I think cannot be other thing than material flexing in several parts or the system. If part of my effort is going towards flexing parts of the bike, that means less braking force.

*I would love to hear from cyclocross riders what type of brakes they use and what kind of descents they travel, I being partly DH rider and used to 203mm rotor disk brakes, get the chills just thinking of descending with drop bars and road brakes...

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A road bike that does not stop quickly & predictably could be very dangerous. Poorly adjusted brakes, an untrue wheel, damaged cables can contribute to poor braking performance. Contaminated braking surfaces can render brakes almost useless. Oil, grease, wax are the usual suspects.

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