Takes place (ideally) before you buy a bike

Bike Sizing is intended to assist you select a bike that has a frame size and shape that is appropriate for your anatomical proportions, riding style, and physical condition - including flexibility and any relevant injuries. A bike of an appropriate size is a precursor to establishing a good bike fit.

There is more to bike sizing than having enough stand over clearance, and there is more to bike sizing than fixating on a frame size. Frame size is commonly an expression of the seat tube length. Manufacturers differ in how this is measured, so two or three bikes from different brands, each with the same published frame size may actually be significantly different in actual size. Or it might be expressed as a generic Small, Medium, Large, leaving the actual size even more open to interpretation, and difficult to compare brands or models.

More important than the seat tube length is the top tube length, as this has a big influence on the seat to handlebar distance, which is a major factor in riding position and comfort.

In addition to the frame size is the frame shape, or geometry. Some bikes are low and long. Some are "square", some are high, but short in length. Some have a lowered front end for more aggressive aerodynamics (and looks), but may be a pain in the neck to ride. So two bikes with the same frame size but a different shape will feel different to ride. And one is likely to be a better fit for you than the other.

Bike Fitting is the process of fine tuning the position of the bike - body contact points in relation to each other for your riding comfort, efficiency and performance.

THE BIKE - BODY CONTACT POINTS ARE:

FEET TO PEDAL  -  BUTT TO SADDLE  -  HAND TO BARS

A bike the wrong size or shape does not allow for an optimal fit position to be established. A bike that is suitable size and shape for the rider will allow an optimal fit to be achieved.

A bike fit is all about adjusting the bike to suit your body, not adapting your body to suit the bike. The bike wont complain about an adjustment, but your body will complain if you are asking it to adapt to a poorly fitted bike. Although some riders have a high tolerance for a poorly fitted bike, the further, faster or harder your ride, the more likely issues of mis-fit are likely to arise, even on a bike of a suitable size.

An initial bike fit involves using the information from the sizing process to establish a sound bio-mechanical starting position for the rider to experience. Initial adjustments result in a seat and handlebar position within normative ranges for the rider, and these can often be established and set up by an experienced rider. But who is normal, or average? A comprehensive bike fit requires an experienced third party to interview, measure, observe, assess and interpret the myriad factors that influence an optimal bike fit, and work with the rider to achieve a happy relationship.