I have an OT bike built up of a standard Columbus SL tubeset that has a pretty agressively ovalised seat tube above the BB. I think it seems harder
to cause chain rub on than an unovalised iteration of the same tubing, and
of course there's no weight penalty. Kurt Sperry Bellingham WA
On 8/4/05, Mark Bulgier <Mark@bulgier.net> wrote:
>
> Martin Needleman outed his eBay Zunow
> http://ebay.com/
>
> In the entertaining and accurate auction description, he describes the
> various decals and what they mean, all but one: "There is also a decal
> which reads 'Zunow Horn System' and I haven't the foggiest idea what
> that means."
>
> Horn System refers to the special seat tube. It is normal 28.6mm
> (1-1/8") over most of its length, except just below the front derailleur
> it flares or "tapers up" to 31.7mm (1-1/4"). Actually that's the
> dimension it would be if it were left round - it is ovalized such that
> the front-to-back dimension stays about 1-1/8", increasing the
> side-to-side dimension to about 35mm (1-3/8").
>
> This is an excellent design, which I have used on lots of frames. (Used
> to be, any framebuilder could buy this tube from Tange - don't know if
> it's still made.) On most any normal diamond frame, (i.e. not counting
> Rigi, Thanet and other "funny" bikes), the sides of the seat tube at the
> BB shell see a very large stress, as evidenced by the frequency of
> fatigue failures there, and the flex that causes the noticeable chain
> rub on the F. der. cage. So adding the minimal extra weight of this
> flare is grams well-spent.
>
> Other brands (notably Serotta) took it further, making the large part of
> the seat tube larger still, and running the large part farther up the
> tube, but this adds more weight and prevents using normal clamp-on front
> derailleurs (talking period equipment here). Also I think it is out of
> balance, if the other tubes are normal - I like stiffening up the seat
> tube just enough to bring its stresses more or less to the same levels
> the rest of the frame. My gut reaction is the Horn System is a balanced
> design with few drawbacks.
>
> Mark Bulgier
> Seattle WA USA
>
> _______________________________________________
>
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