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If I would pay for a professional bike fit right now for a road bike, and I get a new road bike after a while, can I somehow translate the fit from my current bike to the new one (either by myself, or at a mechanic)? Or would I need to pay for a complete bike fit again to get a comparable fit?

Comparing to e.g. glasses: is the result of a bike fit like a prescription that holds value on its own, and can be re-used when getting new glasses?

I am asking this as I have pain in my neck and shoulders during cycling. I am considering getting a bike fit on the short term, but on the longer term also expect to get a new bike. Depending on the answer to this question the order of these two things might change.

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    Do you wear a helmet with a visor/brim ? If so, try removing that from the helmet. They can make you crane your neck on road bikes.
    – Criggie
    May 26 at 19:37
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    Thanks for the suggestion. Iwear a helmet, but without visor, so no easy fix there. May 27 at 13:04
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    I'm lucky and privileged and have a physical therapist that can bill bike fits to my insurance (yay, America /s). It's surprising how different all 5 of my bikes are (two drop bar bikes, two flat bar MTBs, and 1 drop bar bike converted to flat bars).
    – Paul H
    May 27 at 23:43
  • @SaaruLindestøkke, it might be that the bike shape itself is not right for you, some people will never be pain free on a road bike (or mountain bike or whatever they selected.) It might therefor be a good option to try out different bikes. (I went so different that I am on recumbents most of the time now.)
    – Willeke
    May 28 at 20:49

3 Answers 3

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In the abstract, yes - unless something changes in your body (joint mobility, upper body strength and mass, power output etc), then for a given discipline of riding and with a given set of goals (all day recreational road ride vs racing, say), the fit should be able to translate between bikes.

Where things can go wrong or get murky has to do with the methodology of the fitter in a given situation. And, even if they do the best possible job, the new bike may not position you the same as the old one.

A fitter can use either a fit machine (aka sizing cycle and some other names) or an existing bike. A fit machine is a dimensionally adjustable stationary bike where all the contact points between you and the bike can be adjusted infinitely and independently. They could use either measurements from your body or an existing bike to get starting parameters, and then they'll adjust things until they like the result (hopefully you like it too). The best fit machines have resistance like a trainer and can also swap cranks and handlebars, so the pointed-forward position is virtually identical to what it feels like on a real bike.

With a fit machine, once you've achieved perfection there, you get a set of numbers that describe the spatial relationship of the contact points - handlebar geometry and angle, horizontal and vertical distance from saddle to bars (which is best done in reference to a specific saddle), saddle angle, saddle vertical and horizontal relationship to cranks, crank Q, crank length, etc.

Fitting in this way is good at conceptual purity and ideal for building a custom bike. It's also good at giving you numbers to go bike shopping with, since you can then use the manufacturer geometry charts to ensure you can get your ideal fit on a given bike, i.e. the top tube won't be too long or the highest achievable bar height won't be too low. (Using the numbers in this manner to their maximum extent can sometimes mean modeling the prospective new bike in CAD or on paper, especially if it's an edge case or if you're ordering a stem or other fit-related parts at the same time). In the same way, you might find that compared to your theoretically perfect numbers, the achievable fit is compromised on your current bike.

However, fitting with a fit machine is elaborate and time-consuming, and is not the only valid way of doing it, depending on the client needs. A lot of people want something more casual and inexpensive, which leads to the type of fit work that's done by adjusting parameters on an existing bike. If you do it this way, then no, there is no guarantee that what you come up with can be carried over to another bike. Some fitters who do it this way may have a method for being able to say or not say that the parameters attained are perfect and they wouldn't change anything even in the abstract on a fit machine, which is conceptually possible as a way of doing it but isn't what you'll typically find. Some will spell it out for you if they've found a limitation to what's possible on your current bike, but some may give you the best possible compromise and send you on your way. Doing it that way is practical for a lot of riders and situations and isn't a lazy method per se, but has major limitations when it comes to riders who are having fit issues they're having a hard time solving or have outlier/unusual circumstances.

If one way or another you do get into a fit on an existing bike you want to emulate on a new one, you can use those numbers in much the same way as a fit machine fit to go shopping for another bike based on whether the same fit is achievable.

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  • Just to illustrate the type of fit work that's done by adjusting parameters on an existing bike... there is no guarantee that what you come up with can be carried over to another bike. - I had trouble just trying to carry that type of fit to a new (superficially similar dimensions) saddle on the same bike!
    – Chris H
    May 27 at 15:23
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Yes, bike fitting is valid, assuming the type of the bike is the same so you're not comparing a drop bar bike to a flat bar bike.

However, different handlebar dimensions can mean that not all riding positions are equivalent.

That's how I set up my new bikes. I set up the saddle to be at certain height from a pedal in the bottommost position. (This ensures that if the crank lengths are different, I can still reach the bottom pedal.)

After that, I raise the handlebar to the correct height. This is usually measured as "handlebar drop", how many centimeters the handlebar centerline is below the saddle. However, if you ride on the hoods often, it may be more useful to calculate "hood drop", how many centimeters the top of the hoods are below the saddle. For example a traditional style handlebar has larger "hood drop" than "handlebar drop", but a modern style handlebar may have both "handlebar drop" and "hood drop" as equal.

Then I swap stem to one of different length or adjust the saddle forwards or backwards to ensure the handlebar reach, the distance from the saddle to the handlebar, is optimal. Usually it's best to do major adjustments with stem length and minor adjustments by moving the saddle fore or aft. The saddle movement is restricted by the range specified on the saddle rails, going past that range can break the saddle rails. In theory you could get a seatpost with different setback, but it's usually more expensive than a new stem, and can mess up the relative positions of the saddle and bottom bracket; frames usually have a well-designed seat tube angle intended for a certain amount of setback.

If you want to decide the stem length more carefully, it might be more ideal to choose the stem length only based on riding standing, and then set the saddle to a known distance from the handlebars to make riding sitting natural. In that case, you would measure the horizontal component of distance from the bottom bracket to the handlebars or hoods (standing position) and then place the saddle at a known distance from handlebars (sitting position).

Some factors to consider: handlebar widths and crank lengths may be different on different bikes. You may adapt to the different component dimensions, or you may choose to change the component to have equal dimensions. I have 2cm difference in handlebar widths on two bikes and it doesn't annoy me, also I have 5mm difference in crank lengths on two bikes and it doesn't annoy me either. Larger differences might be annoying.

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An endurance fit isn't the same as a race fit. And a bike built for endurance won't have the same geometry as one built for pure speed.

So I suggest that if you've got a race bike and a distance bike the fit will differ not just because of your different posture, but because of differences in the bike.

As an extreme example, a fit based on the aero bars on a TT bike would position the saddle differently to a fit for touring (and it would probably be a different saddle). The toptube length and stack height will also be so different that just changing the stem wouldn't make the fit match it, and trying to do so would spoil the handling

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  • Thanks for the addition, I'm talking about same-style-bikes where one bike replaces the other, not where one bike compliments the other in a different role. May 29 at 15:12

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