Pre-Purchase Bike Fitting: Bike Buying by Prescription

by | Jan 27, 2023

Most cyclists are mindful of choosing the right bike size when shopping for a new steed, whether you are buying a “screamin’ deal” used bike, or a new dream bike.  But there are some bikes where knowing the right size is not quite enough to guarantee the bike will be a good fit for you.  You need more than a frame size. You need a prescription for selecting not only the model and frame size but also components like the handlebars, stem, and crank length for example.  Bike sizing deals in generalities and averages, but bike fitting focuses on specifics, and a pre-purchase bike fitting helps identify the specifics. Beyond helping choose components, the specifics can also define the saddle-handlebar position in space in relation to the frame.

This is more important for some bikes than others.  Buying a “regular” bike from a bike shop?  No major need for a pre-purchase fit, although it can be helpful.  However, in the following situations going shopping for a bike without a more detailed pre-purchase bike fitting (buying prescription) ignores the wisdom of the proverb:  “measure twice, cut once.”

  • Buying a triathlon “superbike” with a brand-proprietary front end that can’t be adjusted up/down, in or out without hiring, marrying, or becoming your own personal and proficient bike mechanic
  • Buying an “aero” road bike with an integrated handlebar/stem combination
  • Buying either of the above through an online, direct-to-consumer channel

Why might these bikes present an issue, and warrant a pre-purchase bike fitting?

  • Proprietary and/or integrated bar-stem combinations are usually composite (carbon fiber), expensive, and not easily swappable like a regular stem and bar due to the internal cable routing. This makes it hard to test out
    • different equipment choices
      • longer stem
      • shorter stem
      • narrower bar
      • wider bar
    • or different positions (more or less reach and stack to the bars or aero-pads), to find out what works best for you.
  • There are limits to both the interchangeability and adjustability of these front-end parts and your riding position for optimal comfort and performance may not fall within those limits. Meaning you will have dumped a lot of cash into a bike that is not fun to ride and may even be painful!
  • Aero road bikes and triathlon superbikes are more likely to have both the brake and gear cables (or electronic leads) internally routed through the handlebars and stem to reduce aero drag. This makes for a clean look and enhanced performance but comes at the cost of ease of position adjustability.

Triathlon Super Bike P3X with Internally Routed Cables

Triathlon Super Bike P3X with Internally Routed Cables

  • Both triathlon and road bikes have adopted hydraulic disc brakes, which adds time and cost to adjusting brake hose length if needed when the handlebar position is changed. In some designs, the brake hose has to be removed even if you want to move one spacer under the stem.

Aero Road Bike with Disc Brakes

Aero Road Bike with Disc Brakes

For some bikes the handlebar/stem size can be selected at the time of purchase if you know what you need.  In other cases it is pre-determined.  If you don’t know what is going to work best for you, the fate of your riding experience is being left to the brand product manager.  Who do you want in control?

Integrated Bar/Stem Considerations

Triathlon Integrated Bar Stem Combination

Triathlon Integrated Bar Stem Combo

There are a couple of other things to consider with an integrated bar/stem.  The stem is not “flip-able”, meaning it cannot be taken off and turned over to increase or decrease the angle, like a regular stem.  That significantly reduces the height adjustment of the handlebar position to what is available with the underlying spacers. That also limits the height adjustment of the handlebars to say 30mm (a little over an inch) compared to 3 times that by being able to change both spacers and stem angle with a regular bar/stem combo.  If your body doesn’t like where the handlebars are there isn’t much you can do about it.

Another factor is that the handlebar cannot be rotated up or down (there are some exceptions) to find the sweet spot for pressure distribution and ergonomic optimization, which is tech talk for hand comfort.  It is what it is.  If you don’t like it, tough.

There is a saying in bike fitting that “big changes can make small differences and small changes can make big differences.”  However, the change and perceived differences are not always predictable.  Let’s take handlebar width.  For some people the small change between two sizes is profound.  For others, “meh.”  But the reach to the bar might be the difference that makes a difference, and a 10mm stem length change is very noticeable to most cyclists.

Aero Road Bike Front End Examples

Let’s look at a couple of examples from the category of online Aero Road bikes, as far as front-end options go.

  1. Aeroad from Canyon Bikes.  This well know direct to consumer brand offers a svelte aero road bike. The integrated bar/stem is available in 3 widths (39, 41, 43 cm), but only one stem length for each width except for the 41cm bar, which is available in 2 lengths. The choice of bar/stem is allocated to a specific bike size, and you get no say in which one you get other than by choosing the bike size.  Will this specification work for you? Depends on your riding (fit) position. What if it doesn’t?  You may be able to change bars if Canyon has a better size available.  It will also set you back an extra $399 + time and labor to change it out. Or you can return the bike within 30 days.

Canyon Aero Road bar - Pre-purchase bike fitting

Canyon Aero Road Integrated HandleBar – lacks adjustability

2. NS1 from Ventum Racing, who now call Utah home.  The NS1 is a lean mean racing machine that also offers 3 handlebar widths.  But the company empowers the consumer to decide which one, AND they offer 4 different stem lengths for each width.  That is 12 choices in the integrated bar/stem.  Now we are getting some genuine customization options so the bike will suit more people.  But will this bike still fit you and which bar/stem do you choose at the time of order?

Ventum Integrated Handlebar

Integrated bar/stem on the Ventum NS1 Road Bike. Photo by John Higgins

These questions (and more) can be answered through a pre-purchase bike fitting session with a reputable bike shop or bike fitter, but it requires special equipment like a “size cycle”, a selection of bars, and frame finder software to help get the answers.  If you have a strong interest in a specific aero road bike or triathlon superbike, the bike can be mocked up so you can see how it feels to ride on the simulator, or your riding position can be worked out and then the fit co-ordinates can be compared to the bike candidates.

Size Cycle for bike sizing

 Using a Size Cycle to prescribe a bike choice. Photo by Derek Israelsen Photography.

John Higgins

John Higgins

John is an elite level bike fitter who works with non-elite cyclists - although a few have won races! Many don't race at all, but ride for fun, fitness, or to compete against themselves. John has worked with 18-80 year olds (and younger and older), novices, age groupers, masters racers and all levels of weekend warrior. These include road riders, mountain bikers, triathletes, tandem riders, tourers, commuters, bike packers and gravel riders and racers. All share a love of cycling and just wanted to ride more comfortably, and in many cases faster. John is the owner of Fit Kit Systems, and provides bike fitting services through BikeFitr (bikefitr.com)

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