Sizing your bike
Bikes come with different sized frames. These are normally measured from the centre of the bottom bracket (the centre of your pedal crank arm spindle) up to the top of the seat tube (the point where the seat stem is inserted), although some manufacturers measure to the middle of the top tube where it joins the seat tube.
There is a simple calculation to work out the size you need. Stand flat footed on the floor and measure your inside leg. Subtract thirteen inches (33cm) for a mountain bike or eleven inches (28cm) for a road frame. That's the biggest frame size you would need. However since most bikes have quite a lot of adjustment, you can go slightly smaller. So if you're borderline, round down.
