Road Cycling - ovalized downtube and seatstays...what are the advantages?

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veganheart
02-15-04, 01:59 AM
The Morgul-Bismark frame I just bought has ovalized downtube and seatstays. What are the advantages of such a configuration? Anyone tell me anything about Morgul-Bismark as a frame builder? At 2.14 pounds this frame is extremely light. It is built with Easton Ultralite 7005 AL tubing. Its so light that I wonder about its strength integrity.

Thanks for your replies :D

bentbaggerlen
02-15-04, 05:45 AM
The ovalized tubes help to control frame flex. The larger a tube is, the less the tube will flex. But on the same hand, the larger the tube the heaver the tube. You can use a thinner wall to save weight but at some point the wall will become too thin to work with or be easily damaged. To save weight builders will use ovalized tubes.

If you look at many tandems you will find the boob or boom tube that runs from the front BB to the rear BB is ovalized, this is to help control frame flex along the length of the frame.

2.14 lb that just scares me :) When your working on your bike do not clamp the frame in a work stand, it will damage the tube. put an old seat post in the seat tube and clamp to the seat post. I watched in horror as a customer clamped his Cannondale into a workstand and crushed the seat tube.
SuperTrooper
02-15-04, 11:34 AM
I watched in horror as a customer clamped his Cannondale into a workstand and crushed the seat tube.


That just made me ill for a moment. :eek:

demoncyclist
02-15-04, 08:45 PM
The downtube on my Bianchi is ovalized for lateral stiffness. It is round at the headtube, and becomes a horiz. oval at the bottom bracket, to maximize stiffness in the left to right plane, which keeps the bottom of the frame from flexing side to side under pedaling loads. The chainstays are ovalized in the vertical plane to keep them from upwards deflection when I hit a bump. This helps keep the rubber on the road when riding on rough surfaces, also known as New England roads.
sch
02-16-04, 11:22 AM
As demon says, oval tubes are stiffer in the long axis
direction, which explains bi oval tubing on some bikes
with the long axis vertical at the head tube and
horizontal at the BB, as on the Bianchi to increase
stiffness vertically at the head tube and horizontally
at the BB. Of course a horizontal axis would also be
hard to match to the head tube. Oval tubes are easy
to make out of round by gentle compression. Steve