johngwheeler

I am about 177cm (5'9.5) tall and often seem to fall right between two frame sizes for many models, e.g. Trek 54cm & 56cm, Giant M & M/L.

I have chosen the smaller option on my two bikes (Trek Crossrip 54cm & Giant TCX Medium), but am wondering whether I should have gone for the larger size, particularly for the Giant CX bike, which has considerably shorter seat tube (525mm vs 540mm) and top tube (about 20mm shorter than the Trek).

The Trek feels good, but I was able to test ride the 56cm frame without too much discomfort, just a little bit stretched. The Giant now feels a little bit on the small side having ridden it for a few months, and I'm constantly adjusting things to find a "sweet spot". (Note that Giant's sizing charts show the Medium TCX as being suitable for up to 183cm - which seems too much).

So....what are the pros and cons of going larger or smaller for a new rider?

A few things that occur to me are:

1) Smaller frame will weigh a bit less
2) Small frame may be a bit more responsive - no idea if this is true!
3) Large frame could become more comfortable over time as the rider's body adapts and becomes more comfortable stretched out
4) Less (or no) toe overlap on the large frame
5) Less standover clearance on the large frame (e.g. Giant M/L frame only has a about one inch over my inside leg measurement)

Any other considerations?

I really hope I haven't made the wrong decision, because it's an expensive one to fix (new bike :-( )

John.

gsa103

Other consideration:

6) Headtube length:
The handlebars will be higher on a larger frame (assuming same spacers & stem). If you want an aggressive bike, then a smaller frame let's you get the handlebars lower without crazy inverted stems. Alternatively, if you want a more upright position, the larger frame and smaller stem can give you a good position with a horizontal stem.

DrIsotope

You're only talking about 2cm in frame size difference, so the reach and stack are likely about 20mm smaller as well. A longer stem, some spacers under it, and a setback seatpost (if necessary) can easily make a smaller frame fit like one size up. If the frame is too big, your options are more limited.

The problem is, we want to be comfortable, because riding shouldn't be torturous. Guys whose only job is to go fast eschew such concerns-- there are 6' tall guys on the Tour riding 54 and 52cm frames.

nycphotography

^ this. And if you're between sizes, then it's only 1cm. 5mm stem, 5mm seat slide back, same same same.

the main difference is going to be head tube length. the larger frame will have a taller stack height, and may not be able to get low enough w/ zero spacers. the smaller frame will be 1cm to 2cm shorter in the head tube, which creates more drop. this you can't create as easily with stems and spacers, unless you want a stem w/ negative rise.

SkyDog75

You're likely already aware, but height isn't the sole determinant of frame size. It's one of many important numbers, but arm, leg, and torso dimensions also play a part. So do flexibility and personal preference.

That said, you and I are almost identical in height. (I've got you by about a quarter inch. ) I can generally ride 54's or 56's comfortably. I tend to like my frames slightly on the smaller side, which explains why my most comfortable road bike is a 53 with a 53.5 cm effective top tube.

CX bikes can have higher bottom brackets, which means a shorter seat tube length while other frame dimensions remain the same. What's the effective top tube length on your CX bike?

I've seen it suggested (I wish I could remember where) that CX bikes should typically be sized about 2-3 cm smaller than your road bike. I know my own 53 cm CX bike feels considerably bigger than my 53 cm road bike.

Toe overlap on a road bike is pretty much a non-factor. Most of my bikes have some toe overlap, so I have to keep my feet out of the way when turning at very slow speeds. But at any normal riding speed, it's not an issue at all.

johngwheeler

Good point; I forgot that one. This would be one reason for going a bigger frame on the Giant. I've flipped the stem and used all of the spacers and my saddle is still 5-6cm higher than the bars, which puts me in quite an aggressive position.

It sounds like it's easier to correct a frame that's slightly too small (longer stem, setback seat post) than vice versa.

I'm not very flexible yet, and find having bars about level with the saddle (or just below) to be most comfortable, but a 5-6cm drop (as I have on my Giant) is bearable. I'm hoping I'll adapt to the lower position with exercise and increased core strength.

Good points made - thanks!

John

johngwheeler

My BB drop is only 60mm and ETT is 545mm (my Trek is closer to 560mm) so the bike feels tall but short. My inside leg is 845mm (33.25"), so I have long legs for my height. Even so, I find I am on tip-toes when I stop because of the high BB.

Agreed; in practice this isn't much of a problem. Just something to aware of when negotiating a tight turn at slow speeds. I instinctively pedal "heel down" to reduce my toe overlap (I have large feet), or even back pedal to avoid getting my outside foot at the 3 o'clock position when the front wheel is at maximum deflection.

jefnvk

Sizing guides are just that: guides. They work reasonably well to get you in the zone, but fit is very subjective, even more so if you aren't normally proportioned like myself. I personally go towards the bigger bikes, with a long torso it is easy for me to just run the seat lower for my short legs to fit, but it is harder to make a small bike longer.

For recreational riders, there is only one real consideration: comfort. If you aren't comfortable on the bike, you aren't going to derive any benefits from a wrong sized frame that a racer concerned solely with speed might. It seems you may be realizing that already, but you could verify it if you could take a bigger bike out for a bit.

GamblerGORD53

I would get the bigger size and shorter stem every time. I am 5'8" and have been riding 58 / 59 cm bikes my whole life. But these are roadsters with swept bars. More slope makes the fit a bit smaller.
Longer bikes roll along far better. Very seldom am I straddling the TT. Solid as a rock going 45 mph.

gilpi

I'm 6'2" 34 to 35 inch inseam. Currently riding a 58cm and I feel fine with it but my next set of wheels will be 60cm.