Becky: “I bought an old bike from a garage sale, and I want to know what size it is. I have no clue how these things are measured or where to find this out. Can you help me?”
The answer is Heck Yes! Measuring a bike frame is actually super simple. Generally, bikes are measured in centimeters. To find the frame size, grab a tape measure and place it in the center of the crank bolt (basically, the hole where the cranks are connected to the frame, i.e. the bottom bracket). Then, simply take it to the top of the frame at the seatpost (stop where the seat post starts). That measurement is the frame size. Yup, it’s pretty simple!
Of course, if you have a bike with a sloping top tube, you’ll need to do a little more work to find the frame size. For that, you’ll need a level that’s long enough to reach from the head tube to the seat post. Place one end of the level at the top of the head tube, and let it tell you when you’ve got a level line to your seat post. The point where it meets your seat post is the high point of your measurement, so mark that with a piece of masking tape or something similar. Then, simply measure from this mark to the center of the crank bolt as above. Et voila!
Thanks for the question, Becky! Hope you get plenty of miles out of your garage sale find!
Got a burning question? Send it over to me, and I’ll answer to the best of my ability. Because it’s important to remember, there are no stupid questions. And anonymity is really cool too.