Measuring bicycle frame sizes / bike fitting.
How to measure a bike frame:
Bicycles are measured in several different ways. The usual sizing measurement relates to the seat tube length, given in centimetres for road bikes and inches for mountain bikes. The best way to measure the seat tube is from the centre of the bottom bracket shell to the centre of the top tube. Centre to top seat-tube measurements are often quoted (like in the diagram shown here), but in my opinion they aren’t as useful as centre-centre measurements because they often overestimate the size of the frame. This is especially the case with modern frames which now utilise top tubes with humongous outer diameters.
Unfortunately, with the advent of compact sizing, sizing has become even more difficult. As you can probably tell, I’m not a big fan of compact geometry bikes. The main reason for their introduction by the Giant bicycle corporation was to reduce the number of frame moulds required for the construction of their new composite bikes. Increasing frame stiffness, reducing frame weight and improving fit certainly weren’t the first considerations when the idea of compact frame sizing was conceived. I’ve come to loathe them even more when people don’t know how to quote their effective top tube & seat tube lengths. [Read more →]
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