Riding the wrong size bike is like trying to play basketball in Shaquille O'Neal's size 22 shoes-when you've got size 9 feet. You can do it, but it will be awkward and not a lot of fun.

Shopping for a bicycle is a lot like shopping for clothes-it's best to go to the store and try one on. To figure out which size bike you need for yourself or your child, just look below:

Fitting the rider to the bicycle

1. at least 1" of clearance 2. minimum leg length dimension 3. highest part of the top tube

Choosing a bike for yourself
If you're a man, you'll want at least 1-2 inches of clearance between your crotch and the bicycle's top tube, when you stand straddling the bike flat-footed. If you're going to be doing some more aggressive riding, 2 or more inches may be better. Make sure the handlebar is within easy reach-you don't want to have to stretch, or feel too cramped.

If you're a woman, the amount of standover clearance will be the same as it is for a man. But since women's bikes often have sloping top tubes you'll want to measure the clearance from an imaginary top tube-pretend the top tube extends horizontally from the front of the bike, and measure from there. Again, you'll want to be sure you can reach the handlebar easily, without feeling "crowded."

Choosing a bike for a child
One of the most common mistakes people make when buying kids' bikes is getting a bicycle that's too large, so the child can "grow into" it. This might sound like a good idea, but it's not. A child will have a hard time controlling a bike that's too large, and won't feel confident as a result. A properly sized bike will be safer because it will be easier to control, and a lot more fun.

You size kids' bikes just as you size bikes for adults, meaning you are looking for 1-2 inches of crotch clearance over the top tube. Give at least 2 inches of room if the bike is going to be ridden over rugged terrain, as you would with a mountain bike or BMX bike. It's best if you can bring the child with you to the store to size the bicycle. If you're shopping for a bike as a surprise, you can use a tape measure to measure the child's inseam (distance from the crotch to the ground, when standing), subtract an inch or two and then use that as the standover height (distance from the ground to the top tube) for the bicycle. Make sure you measure to an imaginary, horizontal top tube on girls' bikes, just as you do for women's bikes.