gmason

I must have fallen asleep lately, because I just noticed for the first time today that people are building frames that have Al tubes and C lugs.

Has that combination been around for a while? I have seen many using C tubes and metal - Al or Ti - lugs, but never the other way around. I wonder what that says about the frames' characteristics, assuming that the tubes contribute more to things like flex than do the lugs.

Interesting stuff.

roadwarrior

Not sure I understand your comment...BUT, Cannondale took carbon OUT of the Six/13 in the seat tube to make it stiffer and lighter. They expanded the circumference of the tube to 35mm (I had to get a new front derailleur for mine) and it is noticeably stiffer when riding...so if the inference (I think) is that carbon is stiffer than al, not necessarily so...

gmason

I am making an assumption or two:

1. Lugs, no matter what material, are more compact, and usually thicker walled, leading me to think that the lugs don't flex much in comparison to the tubes.

2. Aside from marketing - no doubt a large factor in many cases - there are probably valid reasons why these various material mixes occur.

Therefore, if my assumptions are correct, then the tubes would seem to account for most of the flex in a frame, and perhaps other characteristics. My interest is in what the thinking is - beyond marketing - behind the various combinations.

Along with the reviews I saw re C lugs and Al tubes, I also read a lab review of the Cervelo Soloist C. Much to my surprise, the BB and shell flexed much more than the rear triangle. [N.B. Much is obviously a relative term - not excessive in either case, I think.] Perhaps not a surprise to an engineer, but that seemed counterintuitive to me. Thence my question.