Right now I'm looking at lower end bikes, let's just say, under 1000 bucks for sake of argument. And I tend to be a fairly analytical person, so I'm playing around with the published frame dimensions from various makers while I wait for the store to call me when a particular bike-of-interest arrives. It seems that there is actually relatively little variation in geometry among frames. For instance I've looked at three frame sizes across one brand, and they all have the same Reach within a few mm, likewise for my two old bikes from the early 80s.

This gets me thinking. My body is attached to the bike in three places: Seat, crank, and bars. Hypothetically, relationship between those three points determines, to a good approximation, the fit of the bike. The seat can be moved up and down, and front to back, by a fair amount. This leaves the Reach and maybe the stack height as the only two real variables.

Unless I find a particular bike that's remarkably different from the others (and the salesmen have told me that bikes within a category are all sized similarly), there's not much to fit on a bike without being able to vary something else, i.e., "something has to give," and it's the stem. Maybe hybrids have a hinged stem for this reason. If so, then my strategy for fitting a bike is to get within the ballpark on standover height, take what I get for Reach, and budget for installing a different stem.

Does this sound reasonable? Or am I either 1) missing something major, or 2) over-thinking it? Is fit a reason to buy a more expensive bike, if I can correct reasonable fit issues with a different stem?

Fitting inexpensive hybrids is pretty straightforward, and you can generally use the XS-S-M-L-XL-XXL designations that come with the numeric size (which probably doesn't correspond to any actual dimension of the bike, anyway. Just remember that for men, medium means around 5'7"-5'9", for women, it's around 5'5"-5'6". On these bikes the reach to the handlebar is shorter and higher, but you want to keep the same reach from the saddle to the pedals. The riding position is a lot more upright, so issues like athleticism, flexibility, and general fitness are less important.

One thing I see is riders choosing hybrids that are too large for them because they want a higher handlebar. They often end up sitting too far forward to reach across to the handlebar comfortably. The correct way to do this is choose the size that is right for your height and select a stem, whether fixed or adjustable, to put the handlebar where your hands want to find it.

And don't forget saddle setback and leveling. Bike sales guys tend to ignore this on cheaper bikes, but it's important for keeping you balanced and reducing fatigue. Keeping the nose up a degree or two won't pressure the groin because you're not trying to to rotate the pelvis, an a little setback allows you to lean forward a bit with a straight back.

[MENTION=35857]oldbobcat[/MENTION], thanks. This lines up with my general expectations. I'm 5' 9.5", so I'm right on the dividing line on the typical size guides. Right now I have a sort of yardstick -- my old commuting bike is extremely comfortable to ride, after much effort dialing it in. I've always preferred a relatively upright posture, but not bolt upright, so I tend to set my bars to be level with the seat. And I'm fearless with a wrench, so I can change the stem if needed.