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Frame size changing when going to aluminum ?(5 posts)

Frame size changing when going to aluminum ?Dave Woof
Jul 6, 2001 12:54 PM
I'm moving from a 57 c-c steel Colnago (58 c-t)(fits very well) to a Dream Plus which is aluminum/alloy. What size should I get in the new frame - I know sizes change 'cause aluminum tubes are bigger and all that.

Here's what I would do..Cima Coppi
Jul 6, 2001 1:27 PM
Assuming Colnago's frame geometry is the same between the two frames. If your current 57cm c-c frame fits you well, then measure it from center to top and use that measurement on the Alu frame. This is usually due to the seat tube on alu frames rising >1cm above the top tube, so a c-c measurment will throw you off.

Good luck!!

colnagos all measured the same....C-40
Jul 6, 2001 4:27 PM
Colango only has one geometry chart that applies to all models. All are measured from the center of the bottom bracket to the bottom of the seat post clamp. For all practical purposes, it's the the same as c-t measurement. If in doubt, measure the length of the head tube on your current bike. The head tube length is listed on the Colnago geometry chart. On a 58cm it should be 155mm or almost 6-1/8 inches long. For reference, the head tube on a 57cm is 147mm and a 59cm is 165mm.

With the use of threadless stems, the head tube length has become more important. I won't buy a frame if the head tube is too short, because I hate the look of spacers and high rise stems.
measure the top tube!merckx56
Jul 6, 2001 8:04 PM
make sure the top tube lengths are the same! the seat tube isn't as important because the alu colnagos are measured to the top of the collar. a steel 57cm colnago has a 56 top. the alu colnago with a 56 top is the 58cm. it has exactly dick to do with the bigger tubes.
maybe measure all the tubes...C-40
Jul 7, 2001 10:17 AM
Can't imagine why colnago would measure to the bottom of the seat tube clamp on a C-40 and the top of the clamp on a Dream Plus.

My 55cm C-40 follows the published geometry chart almost exactly. 55cm to bottom of seat tube clamp, 54.3cm TT, setback is 147mm, the head tube is 133mm, which is 4mm longer than the stated 129mm, but this may be due to extra thickness in the carbon fiber lugs.