How do I order the right size bicycle?

Fit, Fitting, Geometry, Sizing -

How do I order the right size bicycle?


How do I get the right size bicycle?


If you are considering buying a bicycle mail-order you probably already have some level of confidence in fitting yourself to the right size bike. This blog is intended to give you some practical insight on how we look at fitting our customer to the optimal size. Given you can’t test ride the bike first that presents a certain level of risk, but we think being aware of a couple geometry numbers can’t easily make this risk manageable, where you feel 100% confident you are getting the right size on the first try. 


What really matters in fitting a new performance bicycle?


I have been fitting bicycles for 20+ years- The number one most important number to me in bicycle geometry is the “effective top tube”. The “effective top tube length” (“L” in the chart above) is a measurement from the center of the top of the headtube to the center of the seat-post on a hypothetical horizontal line- This gives the truest sense of how long a bike is - This gives the truest sense of how long the rider’s coqpit is and allows the simplest and best comparison across different brands of bicycles. I would say 99% off brands publish this number and it is often easy to find charts online for older models. 


The benefits:

Very, very good for comparison of bicycle models across different brands with same or similar application. The effective top tube often does a very effective job comparing “Brand A”’s cyclocross bike to “Brand B”' s cyclocross bike. It may not do a good job comparing “Brand A”'s cyclocross bike to “Brand B”' s road bicycle or “Brand C”’s track bike. Get it?   


The limitations: 

Geometry nerds and purists are quick to point other parts of the frame’s geometry can affect the effective top tube length’s meaning. Head and seat angles, headtube length, headset spacers, bottom bracket height, and differences in reach. These people will argue reach is perhaps a better number for judging coqpit length, but we tend to feel this is just adding needless complication when the customer is almost always comparing 2-3 bikes that are the same application often are very very similar in these other geometry dimensions.     


The adjustments:

Sometimes we may fit a bike and the new model’s effective top tube is 5mm longer or shorter than the customer’s old bike. There are also some additional steps we can take to further fine tune the fit of the bicycle's coqpit including:

1) moving the saddle forward or back on it's rails

2) changing seatposts to one with different head offsets 

3) adjusting the stem length

4) different bar heights or raising or lowering the stem and bars with spacers will affect how much you have to stretch out in the coqpit - One hot brand’s “road racing” model and “road comfort” model may have the exact same effective top tube but the “comfort” model just brings the handlebar/stem up 40mm with spacers to put less strain on the lower back and ride more upright. The key trade off being the upright position is less aerodynamic. 


Common Issues: 

  1. Fixed gear rider is 6’ tall but prefers a 55cm bike frame - We have observed that some fixed gear and track riders go down 1cm in effective top tube. Having a slightly smaller bike is often easier to "muscle" the bike around in racing. If you know what frame size you love we won't talk you out of it
  2. Traditional geometry vs modern geometry - older road racing frames have horizontal top tubes in literal frame construction - they often have a center to center length equal to the center to top of the seat tube - Modern bikes often have sloping top tubes to increase stand over and shorten seat stays - The actual center to center length of a traditional frame is often a good proxy for the effective top tube for comparison purposes. 


How will changes in “effective top tube length” or “head angle” affect my ride?


Relatively speaking, the bike with the longer top tube will also have a slightly longer wheelbase. This lends itself to being slightly more stable at speed and carrying more momentum. The bike with the shorter top tube will generally have a shorter wheelbase and will feel a little bit more nimble and easy to turn into tight switchbacks or corners. It will also feel a little bit easier to control in the air (for those looking for airtime). We are talking about only 5mm to 1cm in overall length so the difference is subtle, but you would be able to feel it if you rode both bikes back to back. 

The head angle - (A1 in the chart) This gives you the truest sense of how fast a bike is meant to be ridden - slacker head angles imply higher speeds - Generally I would check this against the customer’s intended usage type - All things being equal most sizes of the same model will have very similar head angle, but sometimes smaller sizes are specced with slightly slacker angles to created less wheel / toe overlap- Trends change geometry overtime also, many early gravel specific models had road like 73 or 74 degree head angles, but we are starting to see progressive gravel models going as slack as 70 degrees. Head angle can also be moderated by fork offset and stem length.  


Troubleshooting: The new bike vs old bike paradox 

Sometimes the most difficult customer to fit, is the one that is certain their old bike fit perfectly. We sometimes find this customer has been riding a frame that is a centimeter too short or too large, but has been on it  for so long it “just feels right” to them. When this customer gets a bike correctly fitted they often feel “that something is not right”. We think if we did our homework on the original fit (we did) the right solution here is to give it a little time and keep an open mind. The customer often comes back and tells us after the break-in period is over they find the bike now “turns better than it should” or “is more maneuverable than I thought possible”. 


Are we right? Are we wrong? Looking to debate some of the details? Looking to confirm your frame size? Message us

Leave a comment

Please note, comments must be approved before they are published