What Size Bike do I Need?

DRUMROLL PLEASE...

Answer: it's complicated...

 I received a question from a reader in the comments section this summer and I've finally written an article in response as I promised.  (Keep using comments, folks - I do read them and respond when I can - but I have a family and a full-time job; so this "hobby" of blogging sometimes takes a back seat).  Here's the question; my responses; and the article.  Enjoy!    

Greg G said...

Matt, I'm beginning to shop for a new bike, but there's so much to choose from, with barely perceptible differences really. Can someone get fitted for a new bike without knowing precisely what brand they're going to buy? Since no single shop carries all the possibilities, it makes this a much tougher process.  

Matt Magee said...

Greg- Excellent question. Something I should probably answer in more detail with a dedicated post. Thanks for the inspiration. Now, the short answer is: This is actually where you should start! However, we must clearly define that there is a difference between "fitting" and "sizing".

What you're actually referring to is sizing - finding out what "size" or more properly: frame dimensions work best. Fitting is then taking that bike and making it work for you and your individual physiology and riding style. So; start with sizing - because you'll discover then if there are any bikes on your list that will not work ideally for you.

The most common example from my experience is a customer who might be looking at a Specialized Tarmac or Roubaix. While these are close in size or dimension; the head tubes are different enough that we sometimes discover that one is a better fit than another. Often you can reduce the number of bikes that will work ideally simply by establishing a starting riding position first. This is sizing (but is often what stores incorrectly refer to as "fitting") and should be your first step.

It can be hard to find a place or person who will take the time to "size" a bike competently to a potential client - as this is not the "slam-dunk" route to a bike sale. It is however the correct route to a happy, comfortable, cycling experience which a shop worth doing business with should be willing to provide.

After you have been "sized", you are now ready to start testing potential bikes and making a decision on what you like. Then, buy your bike, ride it about 200 cumulative miles, then come back for an exhaustive fitting. I hope this helps and look for a more detailed post on this topic soon!

With a reputation for pursuing excellence in bike fit; I get this question a lot. I figure that there are more of you out there asking that same question - so if I can help; here's some thoughts on the subject:

• Bike size can be a complex issue as different bicycle brands can use different sizing methods. A 56cm in one brand could be considerably larger or smaller in another brand depending on the standard of frame measurement the brand uses. There are at least 3 common standards for seat tube measuring which can each vary by over 1 cm on the same frame yet still denote the relative "size" of the frame.

• Most bicycle frames consist of up to 8 separate tube sections welded or bonded together. A bike with a 56cm seat tube could be made to fit a variety of body sizes depending on the lengths chosen for the other 7 frame tubes yet the 'frame size' based on the seat tube length for all possible variations would still be called a 56cm.

• The length and relative angles of the 7 tubes not included in the "size" description are as critical to the correct fit of a given rider. The dimensional variations of the other tubes can result in geometrical changes to the overall frame effecting specific riding characteristics along with rider positioning. It's possible to get the right "stand over" size but the wrong geometrical specification for your intended use and physical needs. Additionally, some bikes are intended for competitive or high performance riding while others are designed for comfort over the long haul. The right size in a bicycle intended for a different application than you aspire to will result in an improper bicycle purchase.

• Comparing one brand to the next can become the source of a splitting headache at times. Considering all of the variables outlined above; while it is difficult, a few assets make it more manageable. Accurate frame geometry data, a good grasp on your ideal riding position, and an expert in the applied science of bike fitting and "fit transfer" (adapting a riding position from one bike to another as best as mechanically possible). However, a simple sizing can occasionally help narrow the herd by discovering what collection of the above outlined characteristics will best lead to your ideal riding position.

• Your comfort on your bicycle is tantamount to enjoying your riding experience. Given the variables in sizing of the modern bicycle; consulting with a professional is far more accurate than assuming all sizes are similar across multiple brands.  Even when comparing brands within one store; small differences can be found which may mean that a different size in brand "a" fits better than the size which fit best in brand "b".  The best method of determining correct size is to first conduct a fitting and establish the ideal riding position so that data can be applied to the bicycles being considered. Bike shops will often require an appointment and should charge for this service; but as those who have experienced an expertly performed fitting will attest - it is the best money you can spend on your cycling habit; no matter how serious you are or want to be.

I am in the business of discovering who you are and what you need, then matching the perfect bike to you based on a variety of factors. I can do this best with the bikes and brands I stock and sell.  Every bike I sell includes a "Sizing" as a part of the purchase allowing me to insure that you will end up on the correct size. There is no substitute for a complete bicycle fitting performed after you have ridden your new bike a few times - which we always recommend.

While the answer is not a simple one; we hope you find this helpful.  Contact me and let me help you discover your new bike!

Thanks for reading.
Matt.