[bill]

I am thinking about one of these, SLX, supposedly NOS. The guy says that it's a 54 -54, and that it is definitely measured cc in both dimensions. The geometry charts I have been able to find, however, say that Colnagos (recent Colnagos, anyway) with a 54 cc tt have a 52 c-c seat tube. I can live with a 54 seat tube as long as the tt isn't some other kind of size.
Does anyone have insight into Colnago 90's geometry?

 

[colker1]

I am thinking about one of these, SLX, supposedly NOS. The guy says that it's a 54 -54, and that it is definitely measured cc in both dimensions. The geometry charts I have been able to find, however, say that Colnagos (recent Colnagos, anyway) with a 54 cc tt have a 52 c-c seat tube. I can live with a 54 seat tube as long as the tt isn't some other kind of size.
Does anyone have insight into Colnago 90's geometry?

ask him to measure the head tube length. that plus what you already have will give you all the info you need.

 

[tmluk]

Old and New seatpost collar clamp.

Yes, Colnago has changed geometry slightly ... or should I say the way he spec'ed geometry. And I own Colnago's from the 80's and a recent one.

Early steel version: seat-tube 57-cm (center-top) has a top-tube of 55.5-cm (center-center)
In the late 80's and early 90's, Colnago steel frames do not have seatpost collar clamp. So the center-top measurement is near the top of the top-tube. Therefore, a 57-cm (center-top) would have a 55.5-cm (center-center).

Recent steel version: seat-tube 57-cm (center-top) has a top-tube of 55.6 (center-center).
However, the 57-cm is measured to the top of the seatpost collar clamp for recent Colnago's. Thus the center-top measurement is about 0.5-cm above the top of the top-tube. Therefore, a 57-cm (center-top) would have a 55-cm (center-center)

The best way is to stick with seat-tube (center-top) measurements, not center-center.
I have catalogues from 1990 and a recent one that illustrate the difference.

 

[bill]

this isn't making sense, though (if I try to extrapolate for the 54). Well, I'm not sure that I need to extrapolate anything from what you said. It still doesn't seem to apply, because no one is measuring c-t. I don't think so, anyway.

The seller says that the frame is definitely 54 x 54, c-c in both dimensions. The c-t measurement is not an issue, whether it's measured one way or another way. What I see on recent geometry charts are also supposedly c-c measurements, where a 54 tt is mated to a 52 tt. So, either headtubes have become smaller, with some additional change in geometry somewhere -- it hurts my head, but assuming that the sta and hta have remained the same for the new and older bikes, with a Colnago sta a little steeper than the hta, then the tt is bound to have been lowered for the newer bikes. The result, again assuming that the sta in a new 54 is steeper than the hta, is that the tt is going to be effectively a little teensy eensy bit shorter for the newer bike. a teensy eensy bit.