A very hypothetical frame size question.
 

Suppose you're about to bid on two classic Italian road bikes. Both are in excellent condition, both are priced the same. One has a frame size of 56 cm and the other 58 cm. Your frame size is 57 cm. Which do you buy and why?

TSapp

depends on top tube length :)

The one you like better.

^ This.

But, assuming your 57cm bike and the other two are more or less square, I'd choose the 56cm. Going down one cm is easier on me than going up one cm.

I would lean towards the 56 cm frame because of the stiffness advantage of smaller frames. You would surely have enough saddle height and bar reach adjustability to suit your metrics with just a 2 cm difference.

-G

Will you be using the bike for the same purpose as your current ride? Assuming that it isn't for touring/rando, I'd go with the smaller size.

It really depends on your fit. I think C&V bikes look a little silly if they are too small. Then again, 1cm is not going to be particularly noticeable. It would be important to know the TT length though.

What is the effective toptube length of both bikes?

If the 56 and 58 numbers are the actual measurement, I'd go 56. It's whole lot easier to gain cockpit distance (with a longer stem, longer reach bars, and setback seatpost) than it is to try and shorten it.

Gee! Since it's hypothetical, the answer is easy!

Buy them both. Ride each of them until you decide which you like better. Then sell the other one for a profit.


All the items raised above are correct, which suggests that what you posit as known simply isn't adequate to decide.

One cm in seat tube length is rarely a significant difference. I have one bike that is 3 cm smaller than my "normal" frame size, but I've set it up to compensate thru use of a setback seat post and longer stem. For several reasons, I really love to ride it.

Having bikes with slight variations keeps you attentive to fit & feel. Changing wheels & tires does that, too.

:D

I'd get the blue one.

What length stem do you have on your 57?
If they are both square, and you can run a shorter stem I would probably go with the larger.
Theoretically, the larger will offer a lower seat height to bars distance without having to raise the bars too much.
(I prefer the look of a lower stem)

I'd go with the smaller one for the same reasons stated above. It is easier to stretch a size to make it fit than to shorten a frame.

This is a pretty good question, actually.

I used to ride 54cm seat tube, but these days I ride a 56cm. As I got older, I found it increasingly difficult to get into and maintain a road bicycle crouch while riding. With this in mind, I tried larger frames and found the comfort factor to improve considerably.

So, think about your comfort and how it will impact your enjoyment. For my money, I would go slightly bigger, but that is because I am old and liking relaxed riding positions more than I used to.

Also, two Italian bikes means little to me. I would need to know what makes, conditions, components fitted and lots more. Size is, indeed, an important consideration but so are the other things.

I found going to a smaller frame helped me with balance and stability,
Pedal choice makes a difference, too, as does crankarm length .
All things being equal, slightly small frame .

This thread is pretty pointless without more info. You need to tell us top tube and seat tube measurements on all bikes + stem size on your "57 cm" if you want to get an answer that is any more than a guess. For example my colnago has a 58cm seat tube and 56cm top tube, my bianchi is 57x57. If you go too small it might work dimensionally but there may be too much saddle to bar drop, that's why I can't fit on a 56cm square bike. All else being equal for the best handling I would go with whatever allows a comfortable amount of drop as well as a 110-120mm stem.

The one with the nicest rack.

+487 top tube length. Then, the one with the best paint.

Also, if it is fleece-bay, seller reputation becomes important.

And unfortunately, don't be surprised if the seller has the size wrong. The last bike I bought on eBay was sold as a 58, it was actually a 55. Fortunately, that's what I needed (I ignored seller's sizing). The one before that, sold as a 56, was a 53 (not so good). It moved to another home anyway. I really can't remember a seller getting size right. Part of the reason is I am looking at the deals, which usually means sketchy info, seller who is less experienced, or whatever.

In this hypothetical case i would buy the one that could get rid off easier than the other in the future...if you pay a lot for something you finally dont like ,after all its only photos until it arrives,then your only option is to sell it to someone else without loosing 50% of your money...