how do i measure a frame?

[Fiona N]

There's another complication with compact frames (sloping top tube). Conventional frame sizes were measured BB to top tube but with a compact this gives much smaller numbers as you're expected to have more seat post showing. As a result, the frame sizes for a specific person could vary by 5 cm or more, depending on how sloping the TT is on the compact, compared to the conventional frame size. So now some frame sizes are 'virtual' i.e. BB to the virtual extension of the seat tube until it meets an imaginery horizontal TT. This gives the frame size equivalent to a non-compact frame so, e.g. 54cm is the same size of frame whether it's compact or conventional, even though the seat tube is several cm shorter in the compact case. In the same way a 'virtual' top tube length will often be given for a compact - this is the horizontal distance between head tube and seat post.

You get the idea - e.g. Specialised (link below) have a frame size 54cm for which the actual seat tube is only 48cm

http://www.specialized.com/bc/SBCBkModel.jsp?sid=09Dolce&eid=117

Fun eh!

 

[mickle]

Nicely explained Fi!

 

[jimboalee]

+ 1, Fiona N

But go and read Ribble's sizing guide.

 

[Fiona N]

+ 1, Fiona N

But go and read Ribble's sizing guide.

Oh no, I don't want to spoil my evening

 

[youngoldbloke]

+ 1, Fiona N

But go and read Ribble's sizing guide.

Just looked at it - whats wrong with it?