Originally Posted by
Barrettscv
Hi Dave,
Thank you for the detailed reply. And yes, the chainstays are very important to creating a rigid structure. I agree that the chainstays are also more important than the seattube or down tube in providing a stable support for the crankset and rear wheel. However, even if the downtube is in tension, the lateral rigidity of the downtube is critical to a rigid housing for the crankset. A BB without a rigid downtube would rock uncontrollably.
I certainly think that steel can be as very rigid in the hands of a skilled builder. However titanium can be rigid, I have no doubts about that.
I'll take a hard look at steel for my next bike. If the frame is truly stiff and meets my needs, I'll go with steel.
Michael
Hey Michael,
Thanks for the thoughtful reply. I think we agree on most things but will have to 'agree to disagree' as they say on the down tube's contribution to drivetrain stiffness. I've attached an image of a 'Slingshot' brand bike and while I don't know that I would recommend this bike I do think is serves as a very good example of what a bike can ride like sans down tube. The Slingshot as a steel cable that is in tension working against a fiberglass leaf spring at the rear of the top tube and this cable does nothing whatsoever to contribute to the stiffness of the BB or the drivetrain........ and yet anyone who has spent time on, one as I have, will tell you that the BB is anything but flexi. The vast majority of the energy transfer on this bike is going from the BB, straight through the c-stays to the rear wheel. The set tube does some to keep things stable but it is mostly geared toward having the head tube and seat tube stay in the same plane for crisp handling. It's really hard to believe until you have ridden one but it works. I'm not a big fan of the Slingshot for other reasons (headtube pushing back under hard braking) but BB stiffness and energy transfer are very good.
When shopping for a next bike I would be happy to recommend builders that work in both materials so you could talk with them.
Enjoy the ride,
Dave