general bike sizing question
 

im looking to buy a two new bikes this winter, a road and cross bike, but seem to fall between sizes in almost every bike I look at (either a 58/59 or 61). My question is, which of the two sizes (either getting the larger size frame or smaller) would give me a more 'upright' riding position? If I went with the smaller frame, I would have a shorter top tube and have to reach less, but would need to raise my seat higher. The larger frame would mean a longer top tube and more reach. I am aware that you can basically make the bikes fit the same if you mess with the stem length and height, etc but am cusious what others have to say.

thanks

Depends. I could fit a small but my LBS mechanic says to go with a medium.

but what was there reason for saying that?

They know my height and build what fits me best. Over a period of time, a bike shop is going to be aware of what suits a rider's needs.

Between sizes is kind of a fallacy. There is no uniform sizing convention from one bike maker to another. If you know bikes, then this will make sense. Size to size, different manufacturers size their bikes differently. Futher, most top makes offer comfort bikes with different top tube to head tube ratio. Even some that are similar here across brands will have a different sta which changes things as well. A newbie needs to make the plunge on something close to what he or she thinks they want. A comfort geometry is generally best to start as few want a racey position to begin with. After 5K miles, thing change and sometimes a lot...you may want that longer top tube and shorter head tube even though your body proportions don't change...only your weight, flexibility and fitness.
For a conditioned rider, generally an upright position is less comfortable than a bit more aggressive position.
Take the plunge, and 2-3 bikes later you will be closed to dialed in if you stick with cycling.

Most often, the head tube length increases much more than the TT length, between any two sizes, so the larger size will give you a more upright position. Going too large will result in an overly short stem, however.

These days, almost every brand has a more recreational line of "comfort" frames with head tubes that are all 20-30mm taller than their racing frames. With these frames, you can have the taller head tube without getting the additional TT length.

As an example, Trek has the Pro fit, performance fit and women's fit in the Madone series. Similarly, Specialized has the Roubaix and LOOK has the Optimum series.

http://www.trekbikes.com/us/en/bikes..._and_geometry/

My rule is to pay NO attention to frame size numbers. I look at the head tube length, with the headset stack height included, the TT length and the seat tube angle to determine the fit. The TT length without the STA means nothing.

what did you mean by this quote

Going too large will result in an overly short stem

did you mean if you bought a bike frame that was too large you would need to buy a shorter stem?

Yes. If you buy a racing frame that is 2cm or more too large just to get the extra head tube length, you might need a 20mm shorter stem. A 90mm stem on all but the smallest frame sizes says that the reach is too long. If you want the bars higher, buy a recreational frame.

Is it necessarily bad to have a short stem, though? One of my bikes started life as my main mountain bike back in the '80s and has been revived as a commuter, loaded tourer and now a singlespeed that lives under the stairs at work for runs to the coffee place. It's had (quill) stems from 150mm down to 70, as I moved the bars around for one use or another. There were differences as they changed, but none of them presented a problem. It takes about 10 seconds to get used to the new feel.
For the OP, I'd be inclined to go with the larger frame. I'm 6'4", which is a little larger than most bike shops can fit with what they have on hand or can order easily. I rode 62cm frames for about 20 years because that's what they had in stock ("We'll put on a longer seatpost for you--it'll be fine"). I rode tens of thousands of miles that way, and thought I was as comfortable as you could get on a bike. When I bought my midlife crisis Atlantis, Rivendell's sizing chart put me on a 65. I was dubious but followed their advice, and it's made a huge difference. Instantly, I could stay on the bike 50 percent longer without being uncomfortable.

The only thing that can be bad about an overly short stem is the lack of knee to handlebar clearance that may show up when pedaling out of the saddle.

In the past there were no head tube length options available, but now there are, so why not be smart and take advantage of a tall head tube model if you need it?

If comfort is the desire, ahead of looks, a flipped up stem can add another 2-3.5cm of height. There is just no good reason to buy a frame with too much reach and then fix it with a short stem.

I've got a short torso, so I use short reach bars to allow a 10mm longer stem.

thanks for the replies people. I guess I will have to crunch some numbers as I still don't really know.

i don't think it is as simple as get bigger is better always or get smaller is better always. the fact you are in between sizes suggests you have unusual proportions. so depending on how you are unusual you might be better going bigger or smaller.

i am odd in that i have proportionately longer torso to legs so i will be better off going with bigger and lowering the seat.

Great idea. You didn't post an actual saddle height, a cycling inseam or your height, so we've got no idea how you are proportioned.

There's a lot of fit info out there. Most always start by measuring your cycling inseam - floor to saddle-like crotch contact in bare feet.

As a ballpark starting point, I set the saddle height so my foot is horizontal with the leg fully extended at the bottom of the stroke. During normal pedaling it then requires a 2-3cm rise of the heel to create the recommended 30 degree bend in the leg while pedaling.

Once you have an approximate saddle height, then the handlebar height can be ballparked and so can the required head tube length.