This post explains cantilever brake adjustment.
Cantilever brakes are unjustly considered to be poor brakes by many cyclists, compared to V-brakes for example. They do have their flaws, but low braking power is not one of those, it is mostly due to poor pad/rim material, and (more often) due to poor adjustment. Cantilever brakes allow the user to choose between stronger braking force, or shorter brake lever travel with weaker braking force. In short, these brakes have adjustable mechanical advantage, which is explained in this post:
Bicycle mechanical brakes – working principle.
- Yoke angle: angle that stranding cable takes from horizontal.
- Caliper angle: angle that brake arm takes from vertical (line from pivot to cable anchor is taken for measurement), at the point when pad touches the rim.
- Cantilever angle: angle between the brake shoe – brake pivot line (D2) and the brake pivot – cable anchor point line (D1).
- Caliper length: ratio of D1 to D2 lengths (how much longer is the brake caliper arm compared to the distance of brake pad from the pivot).
- Anchor angle: angle that brake arm takes to the stranding cable, at the point when pad touches the rim.
- Wide profile: cantilever angle is greater than 90 degrees. Obsolete standard. Has low mechanical advantage and requires brake levers with a high mechanical advantage.
- Medium profile: cantilever angle around 90 degrees. Most MTBs from late 80s and early 90s have such calipers.
- Low profile: cantilever angle below 90 degrees. The main advantage is these brake arms don’t stick out so much, so they don’t catch things (tree branches, or rider’s heels for the rear ones). If not set up properly, these brakes offer good firm feel on a work-stand, but low braking power – that’s why they require special attention when adjusting.
Three factors affect mechanical advantage of a cantilever brake system:
- Brake levers. Lever mechanical advantage depends on the amount of cable pulled and the lever length (distance between the lever pivot and the place where rider pulls on the lever). It is usually around 3.5. For V-brake levers it is around 2.
- Ratio between caliper arm length and distance of the pad from anchor point (D1:D2). This mechanical advantage usually is between 1 and 2.
- Anchor angle – gives mechanical advantage when it is 90 degrees. The further away from that it gets, the less it contributes.
- The main effect on mechanical advantage, especially with low profile cantis, comes from adjusting stranding cable, which effectively alters the yoke angle. The smaller the yoke angle, the more mechanical advantage a brake has, but pads travel less for the same amount of brake lever movement.
The aggregate effect of all the noted factors determines the total mechanical advantage. First factor is determined by lever choice. Second is (mostly) determined by brake caliper choice. The rest can be altered by brake adjustment and this will be explained in the next chapter.
Caliper angle of 90 degrees gives the least mechanical advantage. As the angle narrows, mechanical advantage rises, but pads move less for the same brake lever travel. Up to a point when the advantage starts diminishing, along with decreased pad movement! To make this as close to 90 as possible, with narrow profile brakes the pads should stick towards the rim as much as possible, to make the cable anchors stick out as much as possible. Of course, pads mustn’t be too far from the rim, since the effective angle is the one at which pads touch the rim. It is the opposite for decreasing the angle – pads should stick out towards the rim as little as possible.
Available range of angles depends on caliper type, as shown in the pictures below.
The smaler the yoke angle, the greater mechanical advantage. However, yoke angle of zero would mean the cable passing through the wheel. So the minimal possible yoke angle is one that allows the straddling cable to clear the rim, tyre, mudguards etc.
Yoke angle adjustment has the greatest impact on mechanical advantage of cantilever brakes. Overdoing this can cause problems. Too much mechanical advantage can lead to brake lever bottoming out against the handlebars, before any significant brake force is applied – levers have a limited range of motion. Likewise, too little mechanical advantage leads to weak brake force.
Brake pad distance can be adjusted on most cantilever models. Brake pad distance affects the cantilever angle, caliper angle and caliper length ratio. This is especially important for low profile brakes.
Cantilever angle is rather small with low profile brakes and as the pads wear down, the caliper angle diminishes more drastically, lowering mechanical advantage exponentially. That is why it is good to set low profile brake pads as close to the rim as possible, in order to make the caliper angle as large as possible and yoke angle as small as possible (without the cable rubbing the tyre). In addition, since these brakes have low mechanical advantage, lowering yoke angle will give optimal mechanical advantage – without making it too much (too much mechanical advantage would make the brake levers travel all the way to the bars, without pads reaching the rim).
For wide profile brakes, it is the other way round. Because of the caliper angle, low yoke angle can give too much mechanical advantage. That means too much brake lever travel before the pads even reach the rims. This should be considered when setting up these brakes.
Medium profile brakes are somewhere in between the two extremes.
Changing pad distance from the pivots (moving them closer, or further from the brake caliper arms) effectively changes both cantilever and caliper angle. This is the first thing that should be set up, according to the type (profile) of cantilever brakes used.
After the caliper angle has been set, yoke angle is adjusted by placing one stranding cable end in one side of the calipers, passing it over the hook that is attached on the main cable, then pinching it at the opposite side of the calipers, at the desired length (with models that allow for this adjustment, some have a fixed stranding cable length).
Shorter stranding cable will have a smaller yoke angle, and will require that the hook attached to the main cable be put lower (and longer main cable). Vice versa for longer stranding cable.
As a brake lever is pulled, harder for hard braking, several things happen:
- Pads start moving towards the rim.
- Calipers rotate towards the rim, making the caliper angle narrower.
- Yoke angle increases.
While the effect of greater yoke angle always decreases mechanical advantage, the effect of caliper angle change depends on particular achieved angle and angle change. This can be determined only when tested, feel on the stand can be deceiving. That is why cantilever setup takes some trial and error, and experience can help get it right in less time.
Shimano cantilever brakes of decent quality (clicking on the image below leads to the Amazon on-line shopping – as an Amazon Associate I earn from qualifying purchases):