To test the effectiveness of brakes, follow this procedure.
While sitting on the bike, coast moderately on a flat surface at about five miles per hour (be sure there's no traffic around).
Squeeze tightly on the brake lever that operates the front brake. If the rear wheel feels like it is lifting off the ground slightly, then the front brake is adequate. If not, the brake may need to be adjusted.
Repeat step 1.
Squeeze tightly on the brake lever that operates the rear brake. If the rear wheel skids slightly, brake pressure is adequate (too much skid could mean the tire tread is worn). If there is no skid or you feel a slow response, the brake may need to be adjusted.
If either brake has not performed adequately, check to make sure the levers, brake arms, and cables are pulling properly. Also check that rims are clean and dry.
Brake Cable Adjustment
If the brake is properly centered around the wheel and the brake pads are positioned perfectly on the rim, any further brake adjustments you may need to make will likely involve tightening the brake cable. To do this, follow these steps (see Figure 5-1).
Figure 5-1 BRAKE CABLE ADJUSTMENT
Loosen the locknut where the cable connects to the brake levers.
Turn the adjusting barrel in the desired direction. It will be located either next to the locknut or near the rim brake itself. If the brakes are too tight (the wheels squeak while riding or rub against the brake pads), loosen the cable. If the brakes are not tight enough (insufficient breaking), tighten the cable.
When you have turned the adjusting mechanism to the proper point, the brake pads will be at an optimum distance from the wheels, the point at which they don't rub the wheel when at rest but brake effectively when the lever is squeezed (a few millimeters is good). With perfectly adjusted brakes, the brake levers will only need to be pulled a short distance to stop the bike.
Retighten the locknut while making sure not to turn the adjusting barrel.
If your rim brakes are not properly centered, one brake pad will rest closer to the wheel than the other, possibly rubbing the tire. To re-adjust their position, take the following steps (see Figure 5-2).
Many newer bikes have a small screw on top of the brake arms for centering the brakes. Turning the screw to make fine tune adjustments will often center the brakes properly. If more adjusting is needed, continue to step 2. Note: Cantilever brakes may also have a small centering screw on each brake arm. However, since cantilever brake arms work independently of each other, the problem can usually be fixed by adjusting the distance between the brake pads and the wheel.
Use a flat wrench of proper size to turn the mounting bolt, which attaches the brakes to the fork. Turn the bolt away from the brake pad that is too close to the wheel. The bolt should be tight and difficult to turn, but only a slight adjustment is necessary.
When the brakes are properly centered, test them by flexing them. If they do not remain centered afterward, adjust the mounting bolt further, overcompensating if necessary, until the brakes remain properly centered.
Tighten the mounting bolt so it does not fall out of center.
Figure 5-2 BRAKE CENTERING