There's bound to be a time when you find yourself stranded beside the road or bikepath with a simple yet crippling problem -- a flat, for instance. You can avoid a long walk or an expensive taxi ride home by carrying a repair kit and knowing how to use it.

Your kit should include a can of aerosol sealant, available at department stores and most bicycle shops. Find the puncture and remove any imbedded nails, glass shards or similar holdmakers. Then follow the sealant directions closely. This is a temporary solution; as soon as you get home, have the tire properly repaired.

If the tire is too damaged for the sealant to work, you'll need to change the innertube, not hard if you've read the repair section of any god bike book. Most will tell you how to remove the wheel and use a bicycle tire iron to pry one side of the tire out of the rim. Once this is done, the damaged tube can be maneuvered out of the tire. To complete the do-it-yourself flat-tire rescue, you'll need a spare inner-tube and a pump.

Push the tire aside so you can get the spare tube's valve stem into the rim's valve hold. Then work the tube into the tire. The side of the tire is now ready to go back into the rim. Try to do this using just your hands; a tire iron may pinch the tube.

Once the wheel is back on the bike, the pump will get you on the road again. A pump is an important part of your road-repair equipment since a gasstation pump can blow a tire off a rim.

A basic repair kit that will get you through most common breakdowns can be assembled for about $20. It should include: five-inch vise-grip pliers with cable cutter for replacing broken brake and gear-shifting cable; a set of small bicycle wrenches and a six-inch adjustable crescent wrench for turning almost any nut on your bike; and a small screw-driver for making gearshift adjustments.

Another common problem is a snapped spoke. You can ride on a wheel with a broken spoke but may have to accommodate the wobble by spreading the brake calipers.

If your brake and gearshift cables are old, they probably should be replaced. If you don't master the art of cable replacement, you'll have to allow for diminished stopping ability or fewer gears once a cable breaks.

Chain problems occur infrequently if your bike is well tuned, but they can bring your pedaling to a clunking halt. If the chain has flown off the front chainwheel (the gear teeth that are turned by the pedals) on your 10-speed bike, you'll need to release some of the tension on the chain to get it back on. Push forward an inch or so on the tension wheel of the rear derailleur. The chain can also jam in the rear wheel. Loosen the wheel slightly in the frame and move it forward; unjam the chain and replace it on the gears; return the wheel to its former position in the frame and tighten.

You might want tomake a pre-emptive strike on your tires if they're worn and cracking from dry rot. Try to spot potential breakdowns at home and take care of them before you set out.

Even if you have a one-speed, 1939 Sears clunker, you should still be able to cope with a flat tire on the road. But no matter what kind of bicycle you ride, change for phone calls and extra money for a cab -- carried in your kit -- could become your ticket home if bested by a breakdown.