A Roadie Forever
Join Date: Oct 2014
Location: Portland, OR
Bikes: (2) ti TiCycles, 2007 w/ triple and 2011 fixed, 1979 Peter Mooney, ~1983 Trek 420 now fixed and ~1973 Raleigh Carlton Competition gravel grinder
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Are you riding on a track or on the road? I have never ridden the track. It is different from the road and there may be reasons for a different fit than on the road, but if you are riding a track bike on the road, you want that bike to fit for road riding.
Good fit is a big question. It starts with having the seat in the right place so your hips are the right distance both above and behind the pedals. This MUST be right before you even think about the handlebars. Next you want to establish the lean forward you want. This varies a lot from one person to the next (and for the same person as he goes from beginner to a trained rider or young to old). Now you want to place the handlebars in a location to achieve that bend. (Note I said "a" location, not "the" location. I find I can place my handlebars on a line that rises as it goes forward; that anywhere along that line for about 4" will work with each location being a little different but all being similar in terms of aerodynamics, comfort and power.)
If you can vary your stem height, you can probably adjust the stem height to bring your handlebars to a position that intersects that line. Cool. Bike fits!
The services of a fitter can be invaluable in finding the seat location to start from and a handlebar position (and therefor a point on that line). Having a bike that is a sweet ride can also provide that information.
You can see that the line between your eyes and the hub will intersect the line I have been talking about that runs from somewhere close to the furthest forward and up position it is possible to get you knees when out of the saddle (this may be along the top tube behind the head tube) to the height of the seat and forward of the front wheel. (You want to be on a short portion of that line roughly in the middle.) So that rule of thumb (eye to hub) isn't worthless, but it gives you "a" point and no more. And obviously, if you play with the bike's front end geometry (head tube angle and fork rake, you are going to move that point even though your body and eye location hasn't changed.
To get back to your questoin regarding the 90 and 110 cm stems. If that line I described is for you as it is for me, the 90 and 110 mm stems can give you nearly identical positions if you set the 110 1 cm higher than you would set the 90. (For me, 2 cm more horizontal reach has almost exactly the same effect as 1 cm lower stem. VERY convenient!)
If through a fitter or any other means, you can locate 1) your ideal forward lean and shoulder location and 2) the best bend of your elbow you can locate that line. Get a photo or draw a picture of you in that positon, looking from the side. Take a drafting compass and set it's radius at the distance from shoulder pivot to handlebar in your hand. Draw a circle or arc with the compass using the pivot of your shoulder as the center. Now you will see that for a short distance, you can draw a line along that arc. Put your handlebars on that line. Done!
Sorry, that was a long answer. But your question was not a simple question. Some of us spend a lifetime trying to get it right.