Most bicycle brakes are activated by a set of cables attached to the brake levers, and most brake problems can be solved by adjusting the tension on those cables. They will also need periodic adjustments to keep them working properly.
To test the tension of the brake cables, squeeze the brake levers. If they touch the handlebar grips or get close enough to crush a finger slipped underneath, you need to increase the cable tension. On the other hand, if just the slightest pressure on the levers causes the brakes to squeeze, or if the brake pads rub when you spin the bike wheel without squeezing the brake lever, then you need to decrease the cable tension. Cable tension can usually be changed by turning the barrel adjuster located at the point where the cable meets the hand lever. There are tons of easy to follow Youtube videos that show you how adjust brake cables.
There are a few types of brakes, but most likely you will have rim brakes or disc brakes. The most common rim brakes (V-brakes or caliper brakes) squeeze both sides of the tires from the top of the wheel. Disc brakes don’t touch the rim at all, and instead use small calipers to squeeze CD-sized discs mounted in the center of each wheel. Disc brakes offer superior braking performance, but can be difficult to maintain.
The most sophisticated disc brakes use hydraulic mechanisms to pinch the discs. While hydraulic brakes aren’t impossible to maintain at home, they are a bit more than most people want to tackle. Remember to periodically check the lines and fill them with fresh fluid at a local bike shop. And if your handlebar brake fluid reservoir seems low, take it to a bike shop soon.
Less common are coaster brakes, which don’t use levers and are instead activated by pedaling backwards. These are difficult to adjust yourself and are dangerous if not adjusted correctly, so take your coaster brake to a professional.
Brake pads gradually wear out as you use your bike and are easily replaced. You just need to know what size or type of brake pad to buy. The writing on the worn pads should give you a clue as to what to buy. Brake pads are largely universal, although their mounting systems vary. The beginning of this video explain the differences.
Swapping worn out V-brake pads for new ones takes no more than a few minutes, and usually all you need is a properly sized hex key. We recommend Park Tool Hex Wrench ($14) with the three most common key sizes. It will take you a little longer to replace disc brake pads because the brakes are smaller and more complicated; this video shows some ways to approach pad replacement. In both cases, you must readjust the cable tension after putting on new pads.
You will also need to clean those brake pads periodically. Use an old toothbrush or a towel shop ($3) to get into the gap between the brake and the rim or disc, and use a little brake cleaner ($10) to remove any buildup.
