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In my experience, linear pull brakes (v-brakes) have more stopping power than other types of cantilever brakes (let the flames start ;). Modern road bikes always come fitted with dual pivot brakes. There isn't a massive difference in weight (Similarly priced XTR v-brakes @ 400g (F&R) VS Dura-Ace dual pivots @ 314g (F&R)) so I'm wondering if there is another reason why road bikes don't use linear pull brakes?

  • Is it to do with 'feel'?
  • Are my road brakes rubbish, and most sets are actually as powerful as v-brakes?
  • Obviously, current road levers wouldn't work (well) with v-brakes.. Is it a pure legacy reason that v-brakes aren't used?
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I think your premise is backwards. Dual-pivot road brakes have more stopping power than v-brakes. Road bikes use dual-pivot because they work well, mountain bikes use v-brakes because long-reach dual pivot brakes that could clear knobby tires would have excessive arm flex. –  lantius Jun 14 '11 at 7:24
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Again erroneous. V-brakes were introduced because the direct pull cantilever action allowed more braking force than a traditional cantilever. They are far more powerful brakes. –  zenbike Jun 21 '11 at 20:07
    
I think there is being some confusion between dual-pivot road brakes and cantilever. –  heltonbiker Oct 26 '11 at 12:14
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The same is true of a dual pull road cantilever. The leverage is so much shorter, because the length of the arm is shorter, that actual braking force applied to the rim is significantly lower. A road bike doesn't typically need a great deal of force, and they are more than adequate for the purpose. But that is why touring bikes, which carry much heavier loads, generally use canti's, which allow greater braking force, and are still compatible with the cable pull length on a road brake lever or STI lever. A v-brake requires a different pull ratio, and so is not used. Or, lately, disc brakes. –  zenbike Jan 6 '13 at 8:23
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@DanielRHicks: I realize they can be made. But I was discussing what is actually on the market. And what I was pointing out is that v-brakes, because of their design, have a greater mechanical advantage than cantilevers or dual pivot brakes. What they could make, but don't, is irrelevant since I can't put it on my bike. –  zenbike Jan 6 '13 at 17:38

8 Answers 8

up vote 7 down vote accepted

A v-brake has too much stopping power for a road bike, and too little modulation. It requires significantly more contact patch, the rubber area of the tire which is in contact with the road at any given time, to maintain traction in a braking operation. A v-brake has too much power, and too little control of its power because of the linear design of the compression mechanism of the brake. If you managed to get the brake adjusted to work at all, it would cause the bike to skid immediately when the brakes were applied.

In addition the traditional lever pull on a road brake lever uses a different ratio of lever throw to cable pull (1:1). A V-brake (or cable disc or cantilever) uses a 2:1 ratio, which means the lever would have to travel twice as far for the brake to touch the rim. The road brake lever would have to be redesigned.

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What? Narrow-tired bikes with v-brakes and disc brakes are capable of stopping just fine. Also, the Diacompe 287-V, Tektro RL520, and the Cane Creek SCRV are all drop-bar levers designed for linear pull brakes. –  lantius Jun 21 '11 at 19:47
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Try again. Disc brakes appropriately redesigned to use a road lever, do stop fine. And are generally in use on cyclo-cross, tandem, and touring bikes which do not use the fairly standard 23c or 25c tire found on most road "racing" bikes. They can be used because there is appropriate modulation in the brake. meaning you can control the braking force applied to the wheel at the lever. As any experienced mechanic will tell you, V-brakes do not have fine enough modulation control to allow this. IMHO, they don't have any. The contact patch on a 23c tire at 120psi is on average 8mm across. –  zenbike Jun 21 '11 at 19:58
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The size of the contact patch has no effect on braking friction, at bicycle energies. The amount of rubber on the road really has nothing to do with the ability of a bike to skid on asphalt. Seriously, check out Amonton's laws of friction: en.wikipedia.org/wiki/… –  lantius Jun 21 '11 at 20:02
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There simply is not enough rubber on the road to counteract the braking force of a V-Brake applied with the on/off modulation they possess. Those bars, BTW are designed for a lever shaped like a v-brake lever, but not. A canti lever uses the same 1:1 ratio as a road lever. Which is why canti and V-brake levers aren't interchangeable. I'd like you to cite a bike available on the market with 23c or 25c tires which comes stock with V-brakes. –  zenbike Jun 21 '11 at 20:02
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Restating again, now that this is an accepted answer: 1) The size of the contact patch has no relevance for either static or kinetic friction, though in this case we're talking about static friction - kinetic only applies once the tire has begun to skid. This is why sprinters can use 20mm tires and don't worry about slipping when they hammer yet you can still skid a Pugsley. You can verify this counterintuitive fact yourself at home with a brick and a spring scale. 2) Multiple linear-pull (1:1) levers already exist for drop bars, but if you don't need the tire clearance, why run v-brakes? –  lantius Jun 27 '11 at 20:17

It may be tradition, and it may be aerodynamics. Note that some roadsters do... Touring bikes have gradually been switching from the traditional cantilevers to V-Brakes. It's for tire clearance mostly. "Good" caliper roadster brakes are very powerful; A set of high-end Shimano jobs (105 or above) will lock your wheel and they are routinely used by pro road racers. They have a minimal aero profile and contribute little drag. They also look good on a sleek roadster. Also, you don't have to weld or incorporate lugs onto your snazzy carbon-fiber fork legs and seat-stays, which results in a "cleaner" appearance and less weight as well; high-end roadsters are all about weight, as you likely know.

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+1 - good point about the aerodynamics and lugs. –  ninjaPixel Jun 26 '11 at 16:23
    
I'm certain that weight and aerodynamics do play a part in the commercial calculation made when a frame is built. And there are some cyclocross and touring, and tandem machines that have started incorporating disc brakes. I haven't seen any that use V-brakes. But if they did, it would not be good design. –  zenbike Jul 4 '11 at 5:00
    
Also, dual pivot don't create fork- and frame-flex while braking, as V-Brakes do (remember Brake Booster?) –  heltonbiker Oct 31 '11 at 13:48

Couple possible reasons. Note that I don't have sources for these.. some of this is based on what's happened to bikes I've owned with both brake types, but I don't have long term data for the designs.

Service life. V Brakes require separate tensioned springs in the left side and right side of the brake. If one side's spring gets weaker with age, the spring on the other side pulls the whole brake out of alignment with the wheel. This forces you to tighten the spring on the weak side, which causes it to get weaker even faster, until you run out of adjustment room on the brake. When that happens, the whole brake needs to be replaced. (Speaking personally, the brake pads outlived the brake)

Traditional brakes use a single leaf spring, rather than two independently adjusted springs, to control the brake. This means that you never have a case where one side ends up being "stronger" than the other.

Next, mounting hardware. V Brakes require mounting lugs relatively low on the fork, or a separate piece of metal on which the actual brake arms are mounted. On most road bikes, carbon forks are used, which makes providing these mounting lugs difficult.

As for your road brakes, on most plain road brakes I've seen locking both wheels up is relatively easy to do in dry conditions, and plenty of stopping is possible in wet conditions. The only cases I've seen where you can't stop well is in oily conditions, and V Brakes don't handle those any better. (Disks are the only brake type that handles "oily" well)

If you're having issues stopping, consider that the brake handles have some affect on how much force you can apply to the brakes. Really short levers do better with V Brakes simply because V Brakes provide more leverage. However, you pay for that leverage with more cable travel. I've been told (though have not verified) that V Brakes can't be used with most road brake levers simply due to cable travel.

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Single pivot road brake calipers, with matching traditional road bike drop bar levers ("aero" levers) will require more hand grip force to stop, compared to common v-brakes and compatible levers. A lot of road bikes have the standard, older stuff, because it's "good enough" and cheap to produce or aquire and assemble. V-brakes also turn off some road bike buyers who don't like "mountain bikes" or "touring bikes".

Dual pivot road brakes are much more powerful, and can work with your standard aero levers.

If you have a v-brake compatible frame, you can use old style levers with the v brakes by using "travel agents" or similar pulley accessories for touring bikes (travel adapters).

You can also buy v-brake compatible road bike aero levers.

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Wow, no one has really answered this properly. I will keep it short. First at the design stage, any lever, with any brake, can be setup to produce an identical pad force given a hand force. You can go wrong either direction, too much leverage or not enough leverage. Too much leverage, aka a too powerful of brake can result in running out of lever movement or one needs a very true wheel to prevent brake rub. The brake can feel spongy.

Anyway, the big advantage of linear pull or v-brakes has to do with cable and housing,arms,etc stiffness and the force in these components. With Linear pull the cable force is roughly half that of road brake cable. This then means the flex is roughly half. This result in a much "stiffer" brake action given equal component stiffness, or it can mean a weight savings by making the linear components less heavy/ less stiff. So by design they are simply a better brake. But of course setup and other factors can always be the more important factor. And of course since front brakes need such a short cable, it doesn't matter as much on a front brake.

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Except that since the cable travel is twice as much, this means that the cable arms on the levers and brakes are twice as long and have 4 times as much flex. –  Daniel R Hicks Jan 21 '13 at 3:54
    
And that, while what you say is true in that if you were redesigning a v-brake from the ground up, you might be able to make one work, that would be a new brake. Not the existing design under discussion. –  zenbike May 17 '13 at 2:33

V-brakes and dual pivot brakes each have an advantage over centerpull designs like cantilevers: less braking force lost to cable flex. With V-brakes and dual pivot brakes, cable flex is minimal if not eliminated outright.

Road bikes do use linear pull brakes; that's what all sidepull brake calipers (like dual pivot) are. The main difference between dual-pivots and V-brakes is not stopping power (they are equal in that regard), but the amount of cable pulled. V-brakes require more, caliper brakes require less; and so each must be matched with a brake lever that pulls the correct amount of cable.

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Any brake design can give all the stopping power you need. It all comes down to efficiency and mechanical advantage. There is the issue of predictability. The thing that doomed the old Campagnolo Delta brakes was their lack of feel and predictability. Braking into a corner on a road bike you need to be able to decelerate as quickly without locking up. On mountain bikes we often intentionally skid the rear wheel to get the bike around. I tend to finess road bike brakes but toggle mountain bike brakes between on and off. Personally I find modern dual pivots to be harder to modulate than the old single pivots but that is probably because I have many more miles on single pivots. In any case, rim bikes on bicycles are long outlived their usefulness. All serious mountain bikes have disk brakes and I'd wager that within a few years all serious road bikes will have disk brakes as well. Disk brakes are better in every way than rim brakes. More power, better control, less maintenance (for good ones anyway).

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More cost, more weight, harder to maintain, a PITA when fixing a flat... –  Daniel R Hicks Mar 5 at 16:43
    
-1 for the propaganda at the end - it's not as clear cut as user10482 might like it to be. Other balancing factors, less aerodynamic, heating problems, require heavier wheels (many more spokes required to transmit breaking power from centre of wheel to the tyre contact) . –  7thGalaxy Mar 6 at 9:34

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