I recently sprung for a pro fitting from a reputable shop in New York. The guy was knowledgeable, helpful, informative-- a real pro. A week later he emailed a draft of measurements for a custom fit, along with a fit diagram. He also made drafts for a few stock bikes, ie, how to make a Cannondale Synapse get close to the custom fit.
My question has to do with the measurements for the Handle Bar Horizontal Distance and the Handle Bar Vertical Distance (measured from the Bottom Bracket).
On the fit diagram these measurements are: 41.7 cm and 66.2 cm.
On the custom draft they are: 41.2 and 66.8.
When I called to ask about the difference he said that when drafting a custom bike he can use any size tube, and therefore the target measurements are factored differently than on the fit diagram, which is used to fit a stock bike, in which the tube size is always the same. That makes some sense to me. But on the couple drafts he wrote up for stock bikes, he used the Horizontal/Vertical target measurements from the custom draft, not the fit diagram.
I'm a bit confused. This is my first pro fitting, and I'm probably going to spring for a custom frame. But I want to make sure I'm doing this right. The fitter seemed like a stand up guy, so I want to give him the benefit of the doubt. But something doesn't feel quite right. Could this be a problem of a pro jotting down the wrong numbers during a busy week? 7's looking like 2's and 2's looking like 8's after a few too many cups of coffee?
I totally agree. Doesn't seem to matter; a couple millimeters here or there. Especially when there is a fair amount of subjectivity in a fitting in the fist place. But if it really doesn't matter, why would fitters bother measuring down to the millimeter at all? I'm still curious to know the answer to my question mostly so I know more about the process and the individual fitter. Thanks again.
Terraferma 650b, Mondonico SL and ELOS, Masi Gran Criterium, Trek 610, Breezer Liberty, Georgena Terry Classic
I've found that for some discomforts moving my saddle or bars just 3 millimeters can help, or adding a half-degree tilt to my saddle. So I think in fine-tuning it can matter.
I'd assume the goal of this custom fit process is first to identify your best fit, then to show how to implement it in a custom frame, then show how to approximate the ideal in off-the shelf frames with off the shelf fit items, such as seatposts, handlebars, and stems.
I don't see why the dimensioning of the custom frame implementation would not match the ideal. The tube lengths and angles can be fine tuned on paper or in software to any degree necessary, as long as its a lugless frame. Lugs can impose constraints on joint angles.
It's easy to see how the dimensioning of the practical frame implementations will not match the ideal. It's mainly due to the fixed dimensions of available parts, starting with the frame and extending through all the other parts.
I think that ultimately it does not matter, because once you get even your custom frame delivered, the settings will have to be made, and then you'll see if the ideal was correct. You may have to fine-tune the custom frame once you get it.
I don't really get what he is saying either. But it seems to me that the handlebar centroid is going to vary. The seat slides up and out with infinite adjustment, but the bars fit based on the thickness of the spacers, and the length of stems. And the starting point for various frames will not be the same so the addition of those items will create some variable numbers.
I like my seat just so, I can feel an 1/8"/3mm bigtime, but with the bars I can ride the drops or tops or hoods, and many positions in between so there is more flexibility at that end. If I want to adjust the bars, the increment of adjustment is relatively coarse.
FWIW, in my (grumpy old) opinion, the "fit gurus" measure down to the millimeter because it enhances their aura of being, well, gurus. This business of paying an "expert" to wave a dead cat, mutter an incantation, and adjust your seat height by three microns is nonsense, IMO, and with few exceptions, the stories of "...and I was then four MPH faster and felt like I was sitting on a La-Z-Boy!!!" are brilliant demonstrations of placebo effect.
Take a good look at Sean Kelly. The number one pro cyclist throughout most of the 1980s. One of the worst positions I have ever seen from any racing cyclist.
Thanks SixJours, Road Fan and Peterpan for your comments. My former bike probably gave me a position akin to Sean Kelly's. But I'm coming back to cycling after a serious knee injury so now have to be super careful about alignment etc., so I'm thinking those 3 or 4 millimeters are probably gonna matter. It seems like most things can be adjusted after the bike is built and miraculously comes out of the box (one day). The only thing I'm worried about is that these two different measurements make me think one of them is the correct custom fitting and the other is not, but it's not clear which is which. It'd be a shame to throw all these ducats on a pro fitting and custom build if the fitting was off to start with. I'm going to check out the workshop of the builder later on, so probably the thing to do is bring the two drafts to those guys and get their read on the sitch.