choosing bike size when between sizes?

I'm eying a new carbon ride....and I'm finding that I'm sort of between sizes. The smaller size (47) feels a bit short, but currently has a 90mm stem. The larger (50) has a 100 mm stem, but feels ever so slightly long. Those who have seen me on both say to go with the larger, but I'd like to hear some feedback from others who have been in the same situation so that I don't end up with an expensive case of buyers remorse.

I should note that, in either case, a narrower handlebar will be required, and will likely be shorter than the stock bar. The stock bar has a 100 mm reach- the bars I'm looking at have ~80mm reaches.

Thoughts? TIA!

Have the shop change out the stem length on both (make the smaller bike's stem a hair longer, and the larger bike's stem a hair shorter) and see if that makes a difference. A good shop should be more than happy to do this for a test ride.

If they are set up for it they can also mock up the larger bike with the shorter stem AND narrower bars for you on a trainer. They can do this for a trainer test without actually removing the levers, etc. from the stock bars (though it is a bit annoying since someone will have to hold the stock bars). Still it may be enough to give you a feel if you are still uncertain, assuming they are willing to do this.

The other option is to look at other brands that perhaps have a bike that fits right between those two sizes. I'm assuming you are pretty sold on the model you are looking at though?

I tend to go for the larger one, just 'cause larger frames have smaller seat angles... I do better with a 73 degree seat angle. I hate 74 seat angles or above. 73.5's I can manage.

But if I'm on a 74 degree seat, I'm always shoving my butt off the end of the seat to get to a position that my knees & legs are happy with for pedaling... and I don't feel like I'm riding as fast as comfortably.

But then I'm happy with about a 540 mm reach and don't use shallow reach bars either.

If you want to be aero, get the smaller size, if you want to be more upright, get the bigger size.

Maybe see if the bike shop will set up the larger frame for you with a shorter reach & more shallow bars to try on a trainer. Just sticking putting a new stem and handlebars on it while the other handlebar hangs to the side with shifters might work for sizing.

I would love to try the bar thing out, but my shop doesn't stock them. So I'd have to disassemble one of my bikes, or special order a bar for a bike that I may or may not buy. (I probably should just buy the dang bar...I'll need it sooner or later.)

I should add that the larger frame has a taller head tube, which is really appealing to me. I'm all legs, and it's not uncommon for me to have 5"+ of seatpost showing, which can make for an evil saddle-to-bar drop.

Cat, your comment about the seat tube angle is interesting. Maybe that explains some of the moving around that I do on the saddle. The Bianchi has a pretty steep seat tube.

Yep, I'm pretty well sold on this model. It's what I want and an incredible deal.

Thanks for your thoughts- keep 'em coming! :)

I'd go for smaller. You can always adjust via components.

Maybe just have them change the stem and then pretend the bars are shallow to see how it feels.

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Originally Posted by alpinerabbit

I'd go for smaller. You can always adjust via components.

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I agree.

That works, except for seat angle. Very difficult to adjust the seat angle via components.

Even with a setback seatpost and a longer saddle and changing cranks... I can't make a 74 degree seat angle work for me.

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Originally Posted by Becky

Cat, your comment about the seat tube angle is interesting. Maybe that explains some of the moving around that I do on the saddle. The Bianchi has a pretty steep seat tube.

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Try hanging your butt off the end of the seat on your bianchi and see if it feels more comfortable. (not the seat, but just the riding position)

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'.

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Originally Posted by 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'.

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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.

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.

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Originally Posted by 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.

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This gal does it for a living. Good advice!

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).

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...