One of the most common brake styles found on road bikes today are called caliper brakes (also 'road brakes' or 'road caliper brakes'). Like the medical instrument, a caliper is a tool that hinges and allows two arms to adjust to various widths, either to measure the distance between something or -- in this case -- to provide an adjustable system for pulling brake pads against the rim of a bicycle.
This article will describe the basic function of caliper brakes and help you with some of the basic repairs you will likely encounter if you have these brakes on your bike.
Types of Caliper Brakes
While all caliper brakes are broadly the same, there are three separate types of caliper brakes that vary in style. You should know what these look like to reduce confusion when working on your brakes.
The first type is the single-pivot side pull. These brakes consist of two curved brake arms that pivot, as the name implies, from a central bolt that mounts onto the front fork or the rear of the frame.
The second type of caliper brake is the dual-pivot side pull. Like the single-pivot style, the brake is activated by the brake wire descending along the outside of the brake. However, instead of both brakes pivoting around a central bolt, in this design the cable pulls only one arm of the caliper. The second brake arm is activated by an internal cam, which makes these brakes "center" quite well.
The third type of caliper brake is the center pull design. Not to be confused with two-piece cantilever breaks commonly found on cyclocross and commuter bikes, these brakes are much less popular now than they were in the 1970s but are still around. As the name implies, center pull brakes rely on a brake cable descending towards the center of the mechanism. Here, the cable splits in two and connects to each of the brake arms.
Sizing Caliper Brakes
Before we get into the adjustments, let's make sure your caliper brakes are the correct size for your bike. This can be measured easily. Using a ruler, measure the distance (in millimeters) between the mid-point of the mounting hole and the mid-point of the rim's braking surface.
This distance can then be used to check the brakes themselves. Measure the distance between the mid-point of the mounting bolt to the mid-point of either brake pad. Since the springs are holding the brake pad tight, this is the minimum distance that the brake is compatible with. Flex the spring outwards and away, then re-measure this distance. Now you'll have the range of distances that your brakes are compatible with.
Centering Brake Pads
One of the biggest tricks to adjusting caliper brakes -- like most cycling brakes -- is centering the brake pads so that they engage the wheel at the same time. This is largely determined by the strength of the springs that return the pads to neutral, but can be caused by other issues as well.
Brake pads that are off center can cause strange braking, throw a wheel out of true, or lead to other issues. Caliper brakes tend to have at least two different ways to adjust centering.
Return Spring Adjustment
The first is with the small springs that return each brake arm. If these springs don't have the same tension, each arm will return to a different starting position and result in uneven brake pad application.
Different types of brakes have different methods for adjusting these screws. Keep an eye out for different mounting holes that allow for different tensions on this spring. Other models use small screws to increase or decrease tensionon the return springs. Tension should be the same on both sides of the brakes.
The second method for centering brakes involves the friction on the bolt(s) that the brake arms rotate around. To reset this friction, use an Allen wrench (hex wrench) to loosen the bolt that holds the brake cable in place. Manually rotate each brake arm and assess the friction on each.
If it seems that one arm has more friction that the other, unscrew the bolt that holds this arm in place and gently remove it. Inspect for grit, rust, or lack of grease around the pivot point. Clean out any grit or rust, then re-apply grease and bolt the arm back in place. Check the friction again. Each should have even friction.
Re-tighten the brake cable.
The most common cause for squealing brakes is dirt and brake pad residue on the rims of your wheels. To deal with this, simply take some rubbing alcohol and a clean rag, and wipe down the braking surface of the wheel.
Squeaking and squealing can also be caused by something as simple as new brake pads. If the sound is new, give it a few rides and see what happens. Make sure, as well, that your brake pads are properly "toed in" as described below.
Brake Pad Adjustment
Adjusting brake pads is the same for just about any type of brakes, but we'll include this information here so it's handy if you're conducting some general maintenance on your brakes.
Brake pads should be mounted so that they don't contact the rubber of your tire and don't overlap the inner edge of the rim. The pad should be slightly tilted to the front, or "toed in." This reduces any squealing, increases the lifespan of your pads, and gives more power to your braking.
Before You Ride Again
After any substantial repair to a bike, make sure to test that you have normal function before riding again. This goes doubly true for break repairs. You may find that your brakes seem to work fine on a normal ride, but problems become apparent when you go down a steep hill. Make sure that everything functions ok before you ride more than a single block.