Are you looking to get a new bike.  New for you.  Could be brand new, or used.  Woo hoo!  That’s exciting!
You may be shopping in stores, or online or both. You have different styles, brands, models, and SIZES to choose from.
And you want to know, WHAT SIZE SHOULD I BE ON?

It’s a great question, because this will affect how the bike fits, feels, rides, handles. i.e your riding enjoyment.
The answer to the question is, “it depends”. It depends on a lot of factors:

  • What style of bike you are going to be riding
  • How far, hard, fast
  • What your existing riding experience is like E.g. new to cycling, haven’t biked for years, regular, devoted enthuiast
  • If you have any physical conditions from accidents or surgeries, that will affect your riding position and comfort
  • What your end fitted position will look like for comfort and performance
  • Your overall and relative proportions E.g. height, inseam, torso and arm length.
    • Note that frame sizing based on inseam length alone is rarely sufficient for an accurate sizing.

There are two key things to understand about a bike size:

  1. There is not a uniform, consistent, agreed way to express a bike size, and so the same frame label size between different brands can vary significantly.
  2. Two bikes the same size may be a very different shape, and therefore feel quite different. i.e the geometry of the bike has a big influence as well.

Size is a one dimensional measure that typically relates to the height of the bike, as an actual or theoretical seat tube length.  It may be expressed in inches or centimeters, or as a small, medium, large, etc.

Size does not take into account the length of the bike, or where the handlebars can be.  Length is important because this affects your reach and drop from the seat to the handlebars which determines your upper body position.

Shape is two dimensional, and is defined in the frame geometry charts for each model.
Shape (geometry) is important because this includes not only the bike length, but the proportions of the bike and where the handlebars can be in relation to the seat, and how the bike will steer.

Shape can be expressed descriptively.  For example:

  • for road bikes as race, competition, sports, endurance, recreation
  • for mountain bikes: XC race, trail, all mountain, freeride, jump, gravity

Shape can also be expressed as frame “stack and reach” co-ordinates, which is a great metric for comparing different bikes.

So to answer the question:

  • You can use an existing bike you are comfortable riding, and measure its frame dimensions
  • You can use online sizing guides: which do vary widely in thoroughness and accuracy
  • You can visit a bicycle retailer or independent bike fitter for a sizing

 

DiFit Kit for bike sizingfferent stores offer different services.  Sizing can be a short simple process, like that provided by bike stores using the Fit Kit System.  This may have no or minimal cost.

Or it can be an hour long process on a size cycle (bike simulator) to determine a final fit position, and therefore suitable bikes. This will typically have a higher cost because of the time and technology involved.

Size Cycle for bike sizing

A bike sizing process should involve questions about your riding history, intentions, style, physical issues and tangible measurements of you on or off a bike to determine either body proportions or joint angles.  If a bike size recommendation is based solely on a quick eyeball assessment, then look for additional evidence to support (or alter) that recommendation.

If you are wanting to get a custom frame built, then the frame builder will have a comprehensive list of questions and measurements, the responses to which will factor into the frame design.

A bike fit is important, but that can only be satisfactorily achieved on a bike of an appropriate size and shape for YOU.  Sizing precedes Fitting.