(by Mikedabaker and his sources.... mike sent me this info when I was shopping
for my first mtb)
Try It On For Size. The correct frame size is critical. Riding a bike that is too large or too small can be more than uncomfortable. Your safety may be compromised, you can develop back problems, and even do damage to your knees and ankles in extreme circumstances. Besides that, the wrong size bike simply isn't as fun! Thankfully, all of this can be prevented by following these six easy tips!
1. Clearance. You want to have a certain amount of clearance between the top of your inseam and the bike's top tube when you straddle the bike. You must always have enough room to step off the bike and stand over the top tube flat-footed. Straddle the bike and stand with your back against the front of the saddle; you should have at least 1-3 inches of clearance if you are on a road bike, 2-3 inches of clearance on a fitness bike, and 4-6 inches of clearance on any bike that will go off-road or onto trails. This "crotch clearance" is crucial for safety reasons, as well as how the bike "handles." It also influences the overall comfort of a bike.
2. Comfort. Being comfortable doesn't just mean that the saddle is soft. It's also about how your body feels in relationship to the bike and controls. If you feel too stretched out or cramped, you're very possibly looking at the wrong size bike. Try a couple of sizes for comparison. You may be able to eliminate one immediately. Let the salesperson help you find the right size bike.
3. Arm Stretch. Your arm reach to the handlebar is very important since it affects how comfortable your back, neck and shoulders will be while you're riding. Sit on the bike and reach for the handlebars. On a properly fitted bike, you should be able to reach the bars with a slight bend in your arms. If you have to fully extend your arms or lock your elbows to reach the bars, the bike is too long. It may also just need a shorter stem or a different handlebar, which a dealer can change for you. Again, use comfort as your guide. If your back feels strained or begins to hurt, you're probably reaching too far forward and you're on the wrong sized bike.
4. Hands. Sitting on the bike with your hands on the handlebar, you should be able to reach the brake and shift levers easily. Levers can be moved, but this is a good way to make sure your arms aren't stretched out too far. If they are, you'll feel additional strain in your hands, and just reaching for the brake levers may be a problem. Everything should be within a comfortable reach. (Please note that the "reach" on some levers can be adjusted. Ask your dealer for details.)
5. Legs: Top of the Pedal Stroke. Sit on the bike and have someone hold you up so you can put your feet on the pedals, or prop yourself up with an arm by sitting on the bike right next to a wall. Pedal backwards, rotating your legs for several crank revolutions. Your knees should never bend to the point that your thigh is fully horizontal. It should be just below horizontal at the very top of the pedal stroke. This will help ensure an ergonomically correct pedaling position, and reduce the likelihood of leg injury or discomfort. If your leg does go to horizontal or beyond, the saddle is too low or the bike may be too small.
6. Legs: Bottom of the Pedal Stroke. Here's the second half of the leg-sizing process. Still sitting on the bike, pedal backwards again. As your foot reaches the very bottom of the pedal stroke, make sure that your knees and ankles are not fully extended. There should always be a slight bend at the knee and ankle joints. This will help prevent knee and ankle injuries and maximize your leg power. FINE-TUNING Even if you did all your shopping and got the bike you wanted - perfect fit and all - it's not unnatural to want to fine-tune your bike for even more comfort or performance. Once you start riding more, something on the bike that initially felt comfortable might not be as comfortable. Just because your saddle felt fine for 10 miles doesn't mean it will feel good after 100! All you need is to "nudge" things a little bit. This process can really make a difference in comfort and performance, as well as your overall enjoyment of the bike.
1. Seatpost. You can raise or lower your seatpost for perfect saddle height. If you have to raise the post higher than the "limit line" stamped on it, you'll need to get a taller seatpost. If you want to go lower than the post allows, the bike is too small (this should be caught at the fitting/test ride phase). Seatposts are adjusted up and down very easily on most bikes, thanks to the little quick-release lever found on the frame at the very top of the seat tube. If it doesn't have a quick release lever, usually all it takes is a five millimeter Allen (hexagonal key) wrench to loosen the bolt and raise or lower the post.
2. Saddle. For some, the saddle is the most important part of the bike. Thankfully there are lots of different shapes, contours, and padding densities. There are padded covers with high-tech "gel" materials that add support and softness. However, in a lot of cases, no amount of padding will ease the first-time soreness that many novice riders experience. After a while the soreness does go away, but, unfortunately, it takes a little time. Several companies now make saddles specially designed for a woman's anatomy. (Many bike shops will swap comparably priced saddles or let you make up the difference if you want to change saddles when you buy the bike.) As for fitting, saddles can be adjusted forward and back, or tilted up and down. This is done usually by a simple clamp, or on better saddles, by a single "micro-adjust" bolt. Both clamp and micro-adjust bolts are found underneath the saddle, and usually require an Allen wrench to adjust. Others require a 13 millimeter open end wrench or similar to loosen a nut on either side of the clamp.
3. Handlebars/Grips. Handlebars are very easy to change or swap. There are lots of different widths of handlebars, plus there are also lots of different bends and "sweeps" (rearward angle or bend). Some even have different "rises" (how high they go). The most common changes are for bigger or smaller riders who want a wider or narrower handlebar. If your handlebar put your hands significantly more or less than shoulder width, consider changing your bar. If the bar is too large, you can even cut it down yourself. As far as adjusting your bar, it can be rotated by loosening the clamp that holds it in the stem. If it is a flat bar (no rise), the sweep should be horizontal. That is, the sweep should not be pointing up or down, but directly rearward on a horizontal plane. Grips are very easily and inexpensively changed. Once again, personal preference is the key. Some people like big, fat, padded grips, while others like a thinner, more direct connection to the handlebar. See your dealer if you think you'd like a different handlebar or set of grips.
4. Stems. Once referred to as "goose necks," this is the part that holds the handlebar onto the bike. Most stems have some sort of height adjustability, and also come in many different heights, lengths and rises. Combined with the handlebars, you can dramatically change the feel of the control center of your bike by utilizing the adjustment features your stem. Changing your stem is one way to bring your bars closer to you or farther away if you're feeling too stretched out or too cramped. Once again, your dealer can advise you.
5. Levers/Shifters. Brake and shift levers generally are adjustable. The key is to position your shifting and braking controls into a position that is comfortable and easy for you to reach. On "drop" handlebar bikes, such as on the famous 10-speed, there is little adjustment. On mountain bikes and cross/fitness bikes, there's a lot of room for adjustment. You can rotate controls around the handlebar at different angles; plus they can be moved closer to or away from your hands and the grips. On mountain bikes and hybrids, the reach to the brake lever can also be adjusted. The lever can be brought in closer to the bar if need be. Your wrists should be relatively flat when resting on the handlebar. Adjust the controls so that there is as little bend as possible to the wrists, after having set the proper seat and handlebar height.
6. Tires. The tires that come on your bike may not fit your riding style and terrain. In any case, they'll be among the first parts on your bike to wear out, so you'll have to replace them sooner or later. Tires come in many different sizes, widths and tread patterns. One will surely meet your needs. If you have a hybrid bike and find you do most of your riding in the dirt, you may want to opt for a more aggressive "knobby" tire. On the other hand, i f you find that you do almost all of your riding on pavement, you might opt for a faster, smoother tread pattern. Talk to other riders in your area and find out what tires have worked for them.
* differences in top tube slope,bottom bracket(crank) height and front suspension preload heights between manufacturers....a basic good rule of thumb for proper sizing would be to stand with the bike between your legs and pull the bike up to your crotch......measure the amount of space below the front wheel....minimum of 2 inches needed so a 16" bike from 4 manufacturers could have 4 different standover heights. a good but small bike shop is the "bike junkie" in bethpage.....family owned by bikers "bicycle planet" in syosset is a good place to see a huge variety of bikes and accessories
Mikes other tips:
you need about 4-6 inches stand over clearance......
it could be better to get a $1000
entry level bike used for $300-$400 you will get a durable frame with high quality