Obese people often look to bicycling as a way to lose weight. Bicycling will help shed excess pounds, but only if combined with healthy eating and other weight-loss techniques. Some slightly overweight people who try long-distance biking to cut down often find they actually gain weight, because the strenuous exercise increases appetite. An obese person's first challenge is finding the right bike; your average 10-speed won't support 300 or 400 lbs.
Shops and Websites
Check local bicycling stores and look at websites to find bicycles made for extra large people. Some companies specialize in bikes for very heavy people. They typically have strong steel frames, far heavier but far sturdier than the light weight carbon or other metal used on general purpose bikes. Some companies will guarantee bikes for up to 550 lbs. many offer bikes for 300-pounders.
Fat Tires and Rims
Get a bicycle with fat tires and strong rims and spokes. Super-thin tires with 1/4-inch or less of rubber on the road are fine for racing, but not for heavyweight people. Wide rims and big tires support weight better but must be on heavy-duty rims with strong steel spokes. Many mountain bike tires and rims work well for oversized people because they are built to withstand jumps and bounces on hard rocks.
Big Saddle and Pedals
Find a big seat. Even many regular-sized touring bikers look to alternatives to the traditional thin bike seat, but a wider seat is imperative for a big person. Find the strongest seat post you can get and make sure it can be fastened securely so it won't slip under pressure. Get bigger pedals, too, wider and thicker than normal pedals. Use metal pedals, not any made from some lightweight composite.
Cruiser or Trike
Buy a cruiser style, with a lower bar for easier mounting. Many heavy people opt for a frame more like the old-fashioned "girl's bike," with a top frame member sloped sharply down to the seat post. Consider a tricycle -- a number of manufacturers now produce three-wheel cycles, which are more stable for overweight riders.
Look at recumbent styles, where the rider sits at a more normal sitting angle rather than mounted atop a saddle. A recumbent can afford the same amount of exercise but with less strain on back and other muscles. Recumbent bikes also are easier to mount and are less prone to tipping over, an important consideration with overweight riders.
Size the Bike
Have any bike sized to fit the rider. Saddle height, handlebar placement, pedal crank length, even the height and length of the frame all affect the comfort of the rider and ability to ride easily. A person's body is in contact with the bike in three areas: handlebars, seat and pedal. If those positions are not comfortable, the rider will not be comfortable and will not ride as well, as far or as often. Someone 6 feet 5 inches tall will not fit properly on a bike built for a 5-foot person.