performance, especially in wet riding conditions, and oils can accumulate on the rim from handling, road spills and chainlube overspray. Wipe rims clean with a fresh rag and an oil-free solvent to remove deposits and debris. Rim walls wear away over the miles, and at a given point require replacement even if the wheel is otherwise straight to prevent a potentially sudden rim wall failure. Some rims have dots or wear lines to indicate replacement when they are worn away, otherwise rims require replacement when the sidewalls feel concave between thumb and forefinger.
Brake Pad Placement - Brake pads should contact the middle of the rim surface to prevent contacting the tire and causing a flat or diving under the rim and locking up the rim without warning. Particularly on cantilever brakes the brake pad contact patch moves down the rim wall with use and may need to be adjusted before the brake pads require replacement.
Brake Pad Toe-In - The brake pad should be set so that the front of the pad contacts the rim just before the rear of the pad (see image page 74). Toe-in helps to prevent brake squeal, and when set up correctly wears flat with use. Every brake system accommodates toe-in differently—some have conical pads, some have adjustable arms, other older models require the brake arms or pad posts to be bent.
Cables and Housing - New, clean and unkinked cables and housing is an inexpensive upgrade that ensures your brakes are operating as they should. Rust, kinks or broken strands call for cable or housing replacement. Gritty feeling cables can be removed from the housing and cleaned with a light degreaser and rag but you should resist lubing the housing as it attracts dirt in the long term.
Rim brakes vary in quality and construction, and sometimes no amount of adjustment can quiet a squeal or overcome poor stopping power. Every brake has nuances in setup that can drastically affect brake performance. Stopping is important, when in doubt consult your local bike shop.