For anyone looking to sell a bicycle on eBay, not knowing how to correctly represent a bike's size can be particularly frustrating for buyers. Many sellers, and even some retailers, provide the size of the wheel or tyre, however, there are a lot of bikes for all shapes of people that use standard wheel sizes. For example, a short person may buy a bike with 26" wheels and a short frame so they can touch the pedals, but this would be an inappropriate purchase for a much taller person or someone with long legs. In cycling terms, measuring the wheel size gives as much information to a buyer as measuring the shoes you wear with the dinner suit you are selling.
We're Measuring The Length Of The Seat Tube
The internationally accepted method of determining the size of a bicycle is the measure of the length of the seat tube. Or more precisely, it is a measurement taken from the centre of the hole the crank goes through to the top of the tube into which the seat post is inserted.
In the diagram above, the measurement is labelled Fs for frame size.
On some new bikes there is often a label towards the top of the seat tube indicating the size of the frame in inches and letters, while on other bikes this sticker could also be on the head tube (the tube the forks go through). An example of a size is 22.5" XL for an extra large frame.
Unique Or Suspension Frames
On some mountain bikes with a unique frame geometry, such as the one pictured above with a suspension set-up, the frame size is taken in a straight line from the centre of the crank to the top of the seat tube, ignoring all the extra tubes and suspension. When taking this measurement, the tape measure doesn't follow the seat tube or any components of the frame, it is just as if a piece of string is placed between the two points being measured.
That's it. It's very simple.
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