Mechanical Advantage | Squealing | Straddle Cable | Transverse Cable | U-Brakes | V-Brakes ® | Yokes
I have another article on this site which deals with the theoretical aspects of cantilever brakes, with a detailed explanation of their geometry and definitions of various terms. That article focusses on tuning the mechanical advantage of a traditional center-pull cantilever system.
This article has more of a focus on practical setup tips, though I have provided links to the theoretical aspects, for those who wish to understand the theory behind the practical advice.
Rim brakes divide into two basic types: cantilever and caliper.
Caliper brakes are self-contained mechanisms, attached to the bicycle's frame by a single bolt for each brake, front & rear. The arms reach downward from above the tire, and need to be long enough to get around the tire.
Cantilever brakes attach to the sides of a bicycle's frame/fork, separately on each side. They can only be used on bikes that are designed to use them, because they require special brazed-on fittings on the frame. These fittings are commonly called "studs" or "bosses."
Cable IssuesMost brake problems are not caused by poor setup, nor by poor quality brakes, but result from excessive friction or poor installation of the cables. See my article on cables for tips on this topic.
Cable AdjustmentThe most basic brake adjustment is the cable length adjustment. On properly equipped bicycles, fine adjustments may be made without any tools, by turning an adjusting barrel at the end of a length of cable housing. The adjusting barrel for a cantilever brake is normally located on the hand-lever, where the housing exits.
In the case of brake levers which don't have adjusting barrels, the adjusting barrel will be located at the housing stop where the housing ends just above the transverse cable yoke. For front brakes, this housing stop is usually attached to the headset, or to the handlebar stem. For rear brakes, it normally would be fitted to a braze-on near the tops of the seat stays, or would use a bolt-on fitting held by the seat-post bolt.
A very few bicycles are actually supplied without adjusting barrels for the brakes. These are usually bicycles which have frames intended for use with upright handlebars, but have had drop handlebars installed as an afterthought. (Brake levers for upright bars usually contain adjusters; those for drop bars usually don't.) This is not acceptable, and you should not accept a bicycle which does not have adjusters; it is a very minor task to install them, for any competent bicycle shop.
Reach AdjustmentMany brakes intended for upright handlbars feature a reach adjustment, usually a screw or cam. This sets the rest position, and is mainly used to bring the brake lever in closer to the handlebar for easier operation by a rider with short fingers. This adjustment should be as loose as allows convenient gripping of the lever, because if you bring the rest position of the lever in too close to the handlebar, you increase the risk of having the lever bottom out against the bar.
If you change the reach adjustment, you should expect to have to change the cable adjustment as well.
Shoe Adjustment****** smooth/threaded bosses
Toe in to reduce squeal, but not too much or the brakes will become too spongy.
Squealing/SqueakingSquealing brakes is a common problem, and there's no one simple solution to it.
It's caused by the friction of the brakes against the rim flexing the brake arms, which then slip back, grab, slip back, grab, etc. This process happens at such high speed that it often causes an audible vibration.
All brakes do this, but with luck the pitch (frequency) is too high for human hearing.
This is generally annoying, but not a safety issue. Unlike automotive brakes, bicycle brakes that squeal are usually in good functional condition.
Here are some things to try if your brakes squeal:
- "Toe in" the brake shoes, so that the front edge of the shoe hits the rim slightly before the rear edge. Not all brake systems permit this type of adjustment, but most do.
- Clean the rims with a good, oil-free solvent (citrus, alcohol, something like that.)
- If the pivots of your brakes are adjustable, make sure that you've eliminated as much play as possible without causing them to bind.
- Different brake shoes may help. I particularly recommend Kool Stop salmon colored units.
Centering AdjustmentWhen the brake is released, the brake shoes retract away from the rim. Ideally, the shoes on both sides should back off by the same amount. If they don't, the brake is not properly centered. In extreme cases, one of the shoes may not retract, and may rub on the rim even when the brake is not being applied.
If a brake appears off-center, check first that the wheel is installed straight in the frame/fork. If the wheel is crooked, and you maladjust the brake to compensate, you are creating two problems where there was only one before.
If the brake is, in fact, off-center, it is often the result of too much friction on one of the cantilever bosses. Unhook the transverse cable, and try moving each cantilever individually by hand. They should move smoothly and freely, and always come to rest near the same position. If you suspect friction, unscrew the bolt that holds the cantilever to the boss, and remove the cantilever. The surface of the boss should be smooth, free from rust, and coated with grease. If it is rusty, that is usually a sign that the bicycle was sloppily assembled at the dealer who sold it. Use emery cloth or sandpaper to remove the rust, and wipe off the dust and sand. Coat the boss with grease, and re-install the cantilever.
Spring AdjustmentIf your wheels are centered, and your brakes are not, and, if the pivots are properly lubricated and free-moving, the brake shoes should be centered. If they are not, you probably need to adjust the spring tension on one or both of the cantilevers. Different brands of cantilevers feature different systems for adjusting the springs.
- Spring attachment. Most cantilever bosses on newer bicycles have a series of 3 small holes next to the boss itself. These holes are meant to receive and anchor the end of the return spring. Depending on which of the holes you chose to put the spring into, you have a coarse adjustment of the spring tension. The top hole provides the highest tension, the bottom hole the lowest. For most installations, the middle hole is best. (Some bosses only have one hole.) Both sides should use the same position.
- Shimano style cantilevers usually have a small screw on one of the cantilevers for fine balancing. This is usually on the left side of the front brake, the right side of the rear. In the early '90's, this adjustment required a 2mm Allen wrench, but newer models use a Phillips screwdriver.
- Dia Compe style cantilevers often use a totally different approach. The Dia Compe system doesn't use the spring hole in the cantilever boss, but has a separate spring block as part of the cantilever assembly. This spring block is the first part to go onto the boss, and it has a hole for the end of the spring. When the bolt holding the cantilever to the boss is loose, the spring block can turn freely, but when this bolt is tightened, it locks the spring block in place. The spring block has flats for a cone wrench (usually 13 mm) to let you rotate it to provide the desired tension.
Some Dia Compe style brakes have these adjustable spring blocks on both sides, others have one only on one side, with the other side using the normal spring holes in the boss.Note: Brakes which use the adjustable spring block do not use the cantilever boss as a bearing surface; instead, they have a hollow cylindrical bushing (sleeve) which fits over the boss. The outside of this bushing/inside of the cantilever must be greased, as you would normally grease the boss.
- Non-adjustable springs are found in older or cheaper cantilevers. If these need adjustment, you must physically deform them. You can sometimes increase the tension of the spring by unhooking the transverse cable and forcing the cantilever out much farther than it would normally go. If that doesn't work, you may need to slide the shoe in or out of the eyebolt to adjust clearance.
Mechanical AdvantageUnlike most other types of brakes, cantilevers permit different setups which provide more or less mechanical advantage. Mechanical advantage is a key concept, which you must understand before you will be able to fine-tune your cantilever brakes. Mechanical advantage is commonly referred to as "power", when discussing brakes, and it is common for people to confuse this with quality. A brake may be designed for any amount of mechanical advantage, but there is a fairly narrow range that is useable.
Mechanical Advantage-Too Little, or Too Much?People with brake problems often think that they need more "power," when they actually need less! In particular, when modern low-profile cantilever brakes are used with drop-bar type brake levers, the combination produces excessive mechanical advantage. This problem also arises when using direct-pull cantilevers (such as Shimano's "V-Brakes") with levers made for conventional center-pull cantilevers.
Too Little Mechanical AdvantageIf you have too little mechanical advantage, when you squeeze your brake handles, you will feel a nice firm response. In fact, if you just squeeze the brakes of a bike that is not moving, your first impression may be that the brakes are in great shape, because they feel so solid and firm...the problem is, that they don't stop the bike, unless you squeeze very hard on the levers!
A brake system with too little mechanical advantage will push the shoes against the rim quickly, but won't push them hard enough. The levers will feel firm because the shoes are not being pressed hard enough to cause them to flex.
If you have too little mechanical advantage, lowering the cable yoke so that the transverse cable is more nearly horizontal will help. If you have low-profile cantilevers, artificially "widening" the profile will also increase mechanical advantage: set the transverse cable wide enough that the shoes have to be exended inward on their bosses to reach the rim.
In some cases, what appears to be inadequate mechanical advantage turns out to be that the brake shoes are not "grippy" enough; they may be dirty, or dried out, or of low quality. Better-quality shoes can make a real difference. I particularly recommend Mathauser brake shoes, which have good grip and wear slowly.
Too Much Mechanical AdvantageIf you have too much mechanical advantage the lever will be all-too-easy to pull, but it will run out of travel and bump up against the handlebar before the brake is fully applied. Once the lever hits the handlebar, it doesn't matter how much harder you squeeze! If you try to correct this by tightening up the cable, you will wind up with the brake shoes too close to the rim when at rest, which will cause them to rub, especially if the wheel isn't perfectly true.
Excessive mechanical advantage can often be reduced by raising the cable yoke and lengthening the transverse cable, so that it makes a sharper angle around the yoke. Unfortunately, there isn't always room to raise the yoke far enough, especially in the rear of smaller frames.
Shimano makes a special wide yoke that sometimes helps with this. It causes the transverse cable to run at a sharper angle than it would with a conventional yoke.
If you have too much mechanical advantage, as with a touring bike or tandem with drop-bar-type levers, you can, in some cases, use a pulley adaptor to convert your conventional cantilevers into direct-pull units:
Variable Mechanical AdvantageMechanical advantage can vary as the brake is squeezed.
Ideally, it should start out low, so that the brake shoes can be set for generous rim clearance. The low initial mechanical advantage will allow the shoes to move in toward the rim fast, in response to a small amount of hand-lever movement.
As the shoes get close to the rim, the mechanical advantage should increase, so that a small amount of hand force will result in a strong force pressing the shoes against the rim.
Some high-end brake levers, most notably the upper-end Shimano models with the "servo-wave" feature, are designed to do exactly this.
Unfortunately, conventional center-pull cantilevers prouduce exactly the opposite variation! As the lever is pulled, the yoke angle gets sharper and sharper, while, in the case of a low-profile model, the pivot-cable distance decreases. Both of these conditions reduce the mechanical advantage as the brake is applied.
Since the travel increases as the brake shoes wear down, braking performance degrades as the shoes wear, not because the shoes have any less grip, but because the mechanical advantage has decreased.
A form of cantilever brake that works like a centerpull caliper. The "L"-shaped arms cross over above the tire, so the left brake shoe is operated by the right side of the transverse cable. A U-brake uses studs that are above the rim, rather than below the it, as with conventional cantilevers. They use the same type and placement of studs as rollercam brakes do.
In 1986-88 there was a fad for equipping mountain bikes with U-brakes mounted underneath the chain stays. This provided a nice clean look to the seat stay area of the bicycle, and provided a somewhat simpler cable routing. In addition, since the chain stays are larger and more rigid than typical seat stays, the "problem" of flexing of the studs under load was reduced. Conventional cantileves cannot be mounted on the chainstays, because the cantilevers would get in the way of the cranks.
Although U-brakes were cool looking and powerful, the fad died quite abruptly when people actually started using the bikes that were sold with chainstay-mounted U-brakes. They had several serious drawbacks:
In recent years U-brakes have been making a bit of a comeback on freestyle bikes.
- The inaccessible location made it very difficult to service or adjust the brakes.
- They complicated the process of wheel removal.
- They tended to get clogged with mud.
- Due to the high-mounted studs, if you didn't monitor the brake shoe wear carefully, as they would wear, they would hit higher and higher on the rim. Eventually, they would overshoot the rim and start rubbing on the tire sidewall. This is one of the fastest known ways to destroy a tire.
Adjusting U-brakes:First, remove the arms from the studs, make sure the studs are free of rust. Coat the studs liberally with grease (this is VERY important!)
Install the arms with them at their maximum spread and tighten the bolts that hold them to the frame. This is how you set the springs. Only connnect the transverse cable after this has been done.
There is usually a small setscrew on the side of one of the arms for fine adjustment of spring balance.
Set the transverse cable as short as possible for best braking. Check the brake shoe adjustment frequently--due to the location of the pivot studs on these brakes, as the brake shoes wear they hit higher and higher up on the rims. If you don't keep on top of the adjustment, they will eventually start rubbing on the tire sidewall. Many thousands of tires have been ruined by this.
Articles by Sheldon Brown and others Harris
Beginners Brakes Commuting
Frames Gears &
Tandems Touring What's
Accessories Bicycles Parts Specials Tools
Since March 31, 1997
Copyright © 1997, 2008 Sheldon Brown
Back to the Harris Cyclery Home PageUpdated Septmber 15, 2001
If you would like to make a link or bookmark to this page, the URL is: