It's easy to tell a bike's frame size if you are buying one new from the store because it's either printed on the tag or you can ask a sales person. If you are buying a used bike, it's up to you to make sure you are getting a bike that fits you. One of the most common mistakes people make is to think that the tire size tells the frame size. It doesn't. Learn two simple techniques to tell a bike's frame size.
Lean the bike onto its kickstand or against a wall so that it will not move while you measure it. If the bike frame you are measuring is considered to have a traditional "men's" frame (with a straight bar at the top from the seat to the handle bars) use the method of determining frame size in step 2. If the frame has a slanted bar or "women's" frame, skip to step 3.
Measure and locate the center of the top tube that runs from the seat post to the handle bars. Measure down from the center of the top tube to the center of frame where the seat post and the lower tube come together (where the sprocket is). That measurement is the size of the bike's frame in inches. Most big-box stores will list their bike frame sizes in inches (26 inches and so on).
Measure from the top of the seat hole (not the post, but the hole the post goes into) down to the center of the frame where it joins the lower support tube over the sprocket. That measurement is the size of the bike's frame (in inches).
- Don't buy a bicycle frame if you don't understand its size. You could wind up out of a great deal of money with a frame that doesn't fit you. Many advertisers (particularly professional cycle stores) use metrics to describe the size of frames. Use a calculator to multiply the frame size you need (in inches) by 2.54 to find your frame size in centimeters.
- No matter what size bicycle frame you think you need, always try riding the bicycle as well. Some of the newer sport models have such different forms of suspension and construction that you might be surprisingly comfortable on a bicycle frame outside of your expected frame size need.
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