Serotta tubing question C4S vs C5S

[phcollard]

I'm considering adding a Colorado III to the stable, thanks to my girlfriend who recently got a CdA with C5S tubing that I find wonderful. Every time I look at her bike I'm really amazed, and I discover new tubing shapes. This frame is swaged, curved, shaped everywhere! A beauty.

So I was offered a CIII with C4S tubing and I'm wandering the difference between the two. Any idea? Do C4S and C5S share the same shapes for instance?

Thanks!

[CNY rider]

I think the number just refers to the number of butted, swaged tubes.
So C5S has one more special tube than C4S.

[cmg]

C5S tubing is triple butted and C4s is double. What that means exactly i don't know. what i do know is that CdA frame will be slightly lighter than a C4S frame of similar dims.

[oliver1850]

I doubt there's much difference. It may have been simply a supplier change. C4S was a mix of Columbus and Reynolds. I think C5S is all Columbus. C4S was triple butted - see the 1999 CSI description. When the C5S tubeset came out (2005), it replaced the C4S in the CSI, CIII, and CDA. I've never heard any discussion claiming late CSIs are a big step up from early ones.