Fit Question -- upper arm relative to fork.
 

I went in to have my cleats adjusted. While there, the guy who fitted me tried to tell me my 56cm Trek frame was too large (I am 5'10.5", and 56 is supposed to fit me). Here's how he "proved" his point: With my hands on the hoods, he held up a yardstick, aligned it with my fork, to show me how my upper arm (shoulder to elbow) sat several inches behind the yardstick (i.e., behind the fork). He pointed to a poster on the wall where the guy's upper arm was in line with (or slightly behind) the fork. He claimed that means my top tube is too long.

However, the guy in the poster was gripping aero bars on a tri-bike. Doesn't that move the upper body (and arm) forward? Is there any such rule of thumb that the upper arm should align with the fork...whether in the drops or on the hoods?

So how do you feel when you ride the bike? Do you get aches in your neck or in your shoulders?

Towlie,

After riding my bike for a year, I just got a real LBS fit. Here is what I learned: Most of those rules of thumb that go about are just that, rules of thumb. They will not apply to everyone in every situation because not everyone is proportioned the same. Two people on the same size frame (that fits) can look different on their bikes. For ex. one guy may have a really long torso but short arms, while the other might have a very short torso but long arms. Still they can both get into a good position. At least, that's how it was explained to me. My fitting was one of the best $50 I've spent in cycling, because it really reassured me that I was in a good riding position, and that I hadn't spent money on a bike that was the wrong size.

True that. I've worked on my fit for some time and it's pretty good now from my perspective. I've paid for fittings from qualified fitters before, but their advice has never been complete. For me it's been a combination of personal experiment/adjustment along with fitter advice.

However, my focus on this thread is very specific -- I want to know if there is any basis for this particular rule (regardless whether it's universal or just a guide). Because, it seems to me, top tube size should have no influence on the position of your upper arm (shoulder to elbow segment) with respect ot the fork. Rather, it seems your hand position is the only variable affecting that. Because if I were to shorten my top tube 10 inches, but my bars and stem are the same length, it seems like upper arm wlil be same distance from fork (which is co-axial with the head tube).

Is this true?

I got curious and took a picture of myself, on my bike. Coincidently, my upper arm lines up perfectly with the straight part of the fork. The problem is I don't know how it would look on a modern straight carbon fork. Since forks all have different bends in them, this seems pretty meaningless.

I guess this situation is analogous to driving. Some people like to be closer to the steering wheel, while others like to be more stretched out. The best position is probably somewhere in between. Not too close and not too far-->otherwise it would be more difficult to steer your bike.

Well, I'm thinking it's the axis of rotation in question here, which is central to the head tube, and to the fork as well since the fork is mounted to the head tube.

Being I'm in the market for a new bike, I've been running around getting fitted for a number of different makes and models. I'm 5'10" and like an aggressive riding position. When looking at Treks, I was fitted onto a 56cm Trek Madone 5.2SL.

If that was the case, wouldn't it be easier to say your upper arm should line up with the head tube? This sounds like the whole KOPS theory. Someone noticed that alot of people are setup this way and figured that is the correct way to do it without any scientific evidence to support it. See Keith Bontrager's article on the myth of KOPS
http://www.sheldonbrown.com/kops.html

I just tried it and my arms aren't lined up like that. I'm farther back. Just for fun I tried to align my upper arms with the fork and I seemed way too far forward.

That's just me. I've never been professionally fitted, but I'm comfortable.

Here's one of those classic fit pictures. This guy violates the rule.

Fit's so individual that you can't take a fitter's word as the absolute truth, much less a fitter that's pointing to a TT position when trying to fit you to a roadie.

Which fork is it supposed to align with?
http://www.trekbikes.com/images/bike...edium/1200.jpg
http://www.rivbike.com/graphic/Canti-RomSV.jpg
http://www.gitabike.com/images_cart/paca-redd-l.jpg
http://www.cervelo.com/models/P2K-2003-bg.png
Should your position change that much just because of the rake?

No.

I'll qualify...

I hooked up a friend of mine with a ski lift ticket this morning. He does all the race fits for a few cycling teams in the Denver area. So, I took the opportunity to ask him about fit. He got a bit gruff because as he's said a million times "there's no hard and fast rule for bike fitting, it's a very individual process and that's why I charge $180.00 bones and take anywhere from to 2-3 hours per individual."

I'll add...

Seat height and seat fore aft position are far less subject to rider deviation than top tube length, stem length and drop. The latter three are more about rider preference and flexibility.

Thanks all...this is much closer to where I was trying to end up with this thread. I think the guy at the shop is full of it. And I don't know what irritates me more -- the thought that he gave me the wrong advice unintentionally (ignorance), or intentionally (to sell me another bike).

It also goes to show that you can never take a fitter's advice blindly (someone else made this point above). I have been to 2 or 3 people now who the cycling community holds up as being some sort of fitting experts, and who charge a good deal for advice, and I still haven't found a pro fitter who has correctly devised a grand unifying theory of bike fitting.