choosing bike size when between sizes?

[alpinerabbit]

OK, let's put it this way: if you can get the correct knee over pedal axis position on either frame, with saddle positioning/seat post, get the smaller.

If you can't, then don't - but I've learned to err on the side of small, all I'z sayin'.

[indysteel]

OK, let's put it this way: if you can get the correct knee over pedal axis position on either frame, with saddle positioning/seat post, get the smaller.

If you can't, then don't - but I've learned to err on the side of small, all I'z sayin'.

You just took the words out of my mouth. You ideally want a bike that allows you to get your weight properly centered behind the cranks and your knees somewhere either above or slightly behind the pedal spindle. You might want to read the "fore aft" part of the following article on bike fit: http://www.peterwhitecycles.com/fitting.htm

To figure the above out, the shop has to be willing to put you on a trainer and to make the necessary adjustments.

From there, check your reach, keeping in mind that reach can be shortened or lengthened to some degree by changing the stem length and rise. Your choice of bars may also help.

I, personally, think it's easier to make a small bike bigger than to make a bigger bike smaller--within reason.

[lunacycles]

The seat angle issue is important, but only once you know what seat angle is ideal for you.

It is impossible for anyone to really recommend the better bike for you, given how little we know about the bike, and know about you. What may be a benefit about the larger bike is it likely has a longer head tube, which will allow for a less aggressive drop between saddle and handle bar. Depending on what kind of cycling you are going to do, that may or may not be a good thing. Women often like a slightly less aggressive position as far as that dimension goes.

Forums are a terrible place, imo, to get this kind of advice. Too little info, too much subjectivity. Get fit locally--it is worth the expense if you are investing in a nice bike--and go from there.

[Biciclista]

The seat angle issue is important, but only once you know what seat angle is ideal for you.

It is impossible for anyone to really recommend the better bike for you, given how little we know about the bike, and know about you. What may be a benefit about the larger bike is it likely has a longer head tube, which will allow for a less aggressive drop between saddle and handle bar. Depending on what kind of cycling you are going to do, that may or may not be a good thing. Women often like a slightly less aggressive position as far as that dimension goes.

Forums are a terrible place, imo, to get this kind of advice. Too little info, too much subjectivity. Get fit locally--it is worth the expense if you are investing in a nice bike--and go from there.

This gal does it for a living. Good advice!

[ilima]

With a shorter stem and short-reach bars, you could decrease the reach by 40mm quite easily.

With your long legs, you are correct to be thinking of the taller head tube on the larger size.

I ride a 49cm bike with a 80mm stem and short reach bars. Rides great and no handling issues (i.e., not twitchy).

[celerystalksme]

If you're truly between sizes, the rule of thumb is to always go with the smaller frame. What size bike is best for you should be toptube dependent...not stem dependent. A quality shop should be able to take all your measurements and give you the best toptube length for you. If their figure or range falls between two bike sizes, you go with the smaller frame.

Of course, this is mostly assuming you want to be fast and aggressive...