The downtube is it seems to me a more direct load path than the top tube for the major stresses commonly fed into to a bicycle frame- headtube, BB, and rear DO- and I'd thus expect beefing up the down tube, all else being the same, would have a greater effect on useful rigidity.
Kurt Sperry Bellingham WA
On 6/14/06, Philcycles@aol.com <Philcycles@aol.com> wrote:
>
>
> In a message dated 6/14/06 9:05:44 AM, heine94@earthlink.net writes:
>
> >I am not qualified to answer that, as I never have ridden two
> >otherwise identical bikes with just different diameter top or down
> >tubes. However, I doubt anybody else alive today has had that direct
> >comparison, either.
>
> I have some thoughts on this subject. While I haven't made identical bikes
> with oversize top tubes and 1" tubes, I have made identical bikes-my own
> are all
> built to the same plan-with .9/.6 and very light-I think a .6/.4-top
> tubes.
> The result? No difference in the ride BUT these bikes are not ridden with
> a
> load. I have made touring bikes with 1 1/4" downtubes and 1 1/8" top tubes
> and
> they felt quite ridgid. While I'm not calibrated the frames did not feel
> as if
> they were twisting under load-30 lbs front and 30 lbs rear. I also believe
> that
> cast BB shells made a big difference. They also steered nicely under load
> but I build touring bikes in the French style with a lot of rake resulting
> in a
> low trail solution. These bikes steer well with a lot of load in the
> front.
> Just my 2 cents.
> Phil Brown
> San Rafael, Calif.
> _______________________________________________
>
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