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Several factors determine the right bike height for a cyclist, and the accuracy of measuring the right height will largely affect the cyclist’s comfort while riding. Because the incorrect riding position can lead to injury or discomfort, it is important to follow the steps outlined here when determining bike height. Of course, you may go down the more expensive path of a professional fit — which would be appropriate for racers or hobbyists who spend significant hours on the bike, and for those investing in buying custom-made frames — but for the rest of us, determining the best bike height can be relatively easy.
When referring to the size of a bicycle, there are actually several different parts of the bike being measured. The first is your wheel size. Mountain bikes typically come with 26 inch wheels, but a new variant is the 29 inch wheel. These will affect how high the bike frame sits. For example, a 20 inch wheel will come stock on BMX and children’s bikes, which make the bicycle sit much lower to the ground. A road bike comes with 700c wheels, which are larger in diameter than a mountain bike wheel. Generally speaking, if you know what type of bicycle you want, the wheel size will be determined for you. If you’re not sure, ask your local bike mechanic which bike is best for you.
The other measurement in determining the right bike height is the frame size. Frame size is determined by measuring from the top of the seat tube — the tube that your seatpost slides into — to the middle of the bottom bracket shell – or, the bottom part of the frame that connects the crank arms. When standing over the bicycle, the rider should have about an inch to two inches between his crotch and the top of the frame’s top tube. This will give the rider a general idea of the right bike height.
Once the rider has determined which frame size fits him best, he must take one more step in evaluating the best bike height. The seatpost, which connects the saddle to the frame, adjusts up and down so that the rider can customize his riding position. A general rule for the correct seat height dictates that when sitting upon the saddle, with one leg pedaled to the six o’clock position, the leg should be almost fully extended. However, the rider should adjust the saddle so that the knee is bent slightly; this will prevent knee injury, as it keeps the knee from locking or over-extending while pedaling.
Keep in mind that the right bike height is only one measurement of many in determining the right fit for your bike. The length of the top tube, the length of the stem, the height of your steer tube, and several other factors will affect your riding position. See your local bike shop for other measurements that are critical in keeping you safe and comfortable on your bicycle.
I can attest to the fact that an improper seat height can cause some real problems. I had one of those 10 speed bikes with the thin frame and a small seat. I'd ride at least a ten mile loop around town every day and come back exhausted and sore. Other bikes didn't make me feel that way. I took my 10 speed to a local bike store and the manager asked me to mount it like usual.
He took out a measuring tape and measured the distance from my foot in the lowest position to the seat. He told me the problem was my seat was too short and my leg muscles were getting fatigued a lot sooner
than usual. I wasn't getting a full stretch when I pedaled. He raised the seat a good inch or two, and I tried it again. It was twice as easy to pedal and I didn't come home sore. If you're having a lot of muscle pain after a bike ride, it might mean your seat height is wrong.