Road Frame Size
 

What Height should a 48cm c-c road frame fit ?
Is it possible to use certain Seat Post/Stem combination in order to fit to a smaller size bicycle ?

Smallest frame I've ever ridden comfortably is a 50cm. I am 5' 7 1/2" with a 29-30" inseam. That's with the saddle back all of the way and a 130mm quill stem at it's highest extension. Seat Post/Stem combination can be used only to an extent. I couldn't ride that 48cm, but my 5' 2" wife could. Really depends on the rider, but if you're 5' 9" then forget it.

Slope top tube frames are a bit more forgiving of rider size than frames with top tubes parallel to the ground. Leg length variations can be accomadated with longer seat posts and seat to bar distance adjusted with various stem lengths, rise/fall and by using seat posts that bend forward or aft and allow the seat clamp to work in either direction. It has become fashionable among the pros to ride frames 2-4cm smaller than would be expected by classical criteria with these methods. Classical criteria for sizing can be obtained from such sites as www.coloradocyclist.com and other mailorder bike/frame suppliers. 48cm parallel toptube frame is intended for riders in the sub 64" height range, down to cerca 56-58" height, though it might be a stretch for 56".
Steve

I stand 5'8" / 173cm and wear trousers with a 30" / 76cm inseam. Depending on top tube length, I can comfortably ride traditional (horizontal top tube) diamond frames in sizes 54 to 57cm C-T, but 55cm (both Capos and the Bianchi) definitely feels right to me.

It's worth repeating that the "inseam" measurement used to fit bicycle frames is NOT the same as your trouser inseam.

The bike inseam measurement is best taken by standing with your back against a wall in your bare feet and your feet a few inches apart. Place a moderately thick book, spine up, between your legs and raise it until the spine is FIRMLY against your crotch. Mark the wall where the top of the book is located and that distance to the floor is you bicycling inseam.