RE: [CR]Help ID Colnago

(Example: Books:Ron Kitching)

From: "Mark Bulgier" <mark@bulgier.net>
To: 'Mark Poore' <rauler47@hotmail.com>, Classicrendezvous@bikelist.org
Subject: RE: [CR]Help ID Colnago
Date: Wed, 8 Aug 2001 22:47:39 -0700


Mark Poore wrote:
> Just bought a Colnago on ebay that came from Italy. The
> seller said it was an '82. The top and down tube have a groove
> on both sides of the tube running the full length of the tube.
> The chain stays have a groove as well on the inside of the stay.
> This was done to increase stiffness I guess.

My cynical take on this is it was done purely as marketing, to differentiate the product from all those other frames with round tubes. I'm pretty sure they know it decreases the stiffness to weight ratio (unless they have no educated designers or engineers there).

Colnagos are very nice bikes regardless, and have a wonderful history and tradition. The reduction in structural efficiency is slight, and if the tube shaping makes the frame more interesting to the rider, and therefore more fun to own and ride, then I'll grant it has its purpose.

But nerd that I am I just can't warm up to it myself. I still respect the builders who resist the market pressure and continue to build 'em the boring ol' way they know is still best.

Some shaping here and there can have an advantage over round for certain loadings, but I almost hate to open that can o' worms because the exceptions are so few - a little ovalizing or indent in the chainstay for tire/c-ring clearance, a bit of sideways oval at the bottom of the seat tube, and of course oval fork blades for road bikes. Tandems have some places ovalizing makes sense too. Not much else though.

Having aligned over a thousand frames myself by hand (if you'll allow a cheaterbar as still "by hand"), I got a very good feel for how stiff (the initial deflection) and strong (the permanent "set") a lot of frames are - as well as how straight they come from the factory. The goofy shaped tubes are almost always noticeably more flexible than round tubes of the same weight. (you can also prove it mathematically but I prefer the hands-on empirical method) Yes I know road and pedaling stresses don't exactly mimic the stresses applied to align a frame, in direction or magnitude, but the lessons learned are valuable nonetheless. Combined with some basic engineering, reading others' research, inspecting lots of broken frames, and just lots of pondering over the years, builds a pretty good mental model of real stresses in frames.

Scariest frames I ever worked on were the Colnago Bi-Titans with the "Master" shaped top tube and twin teeny downtubes, just amazingly flexible. Never rode one - can anyone tell me, does the rear wheel try to pass the front wheel?

Goofiest tube shaping I can recall was the "Ditchex" (I'm not making that name up either!) top tube on some Zunows - the groove was so deep that the rear brake cable housing snapped into it and was almost internally routed. Columbus made a top tube like this too, held one in my hands, but never saw a frame made with one. Way heavier, weaker and more flexible than a plain top tube, but what a cool gimmick! 80s Zunows made Colnagos look sedate: "Horn System" seat tubes, "Pentagla" chainstays, and the immortal Ditchex - is the Zunow marque still alive?

Well enough ranting, only masochists are still reading at this point.

Tailwinds,

Mark Bulgier
Seattle, Wa
USA