Helix shaped tubes?

[Blaster1200]

Originally Posted by vulture

I wonder if the direction of the twist is specific to the northern hemisphere? I mean whats that thing gonna ride like if it conflicts with the Coriolis force when it is in say, New Zealand or some other southern hemisphere location? I love the bike industry.

I believe they offer two versions: One for the northern hemisphere and one for the southern hemisphere. However, in the southern hemisphere both versions are available and marketed a bit different. The NH version is actually designed for right handed people who are presumably stronger with their right leg. As a result, the twist is designed to counteract the forces applied by the stronger right pedal. The SH version is actually designed for left handers who are stronger with their left foot, and it is designed to counteract the forces applied by the stronger left pedal. If the wrong application is use, the rider risks turning the frame into a pretzel.

[dr.welby]

Originally Posted by vulture

I wonder if the direction of the twist is specific to the northern hemisphere? I mean whats that thing gonna ride like if it conflicts with the Coriolis force when it is in say, New Zealand or some other southern hemisphere location? I love the bike industry.

You have to twist the head tube and the down tube in opposite directions so they cancel out (of course accounting for the different outside diameters with the amount of twist angle).

[dpugh5]

Originally Posted by dbohemian

Just because I was curious.

I modeled two tubes. Made it real simple and FEA is only as good as the info in and this is a simple beam bending example. Not very fancy.

One was a .6 wall 1.5 tube round and the other was a helix tube same size, same thickness.

I applied a 100lb load in one direction while fixing one end. Tubes weigh the same within a few grams.

Bottom line as far as displacement is concerned. Round tube flexes 12.35mm and helical tube flexes 15.08mm. Helical tube is not as stiff as a round tube. At least in pure sideways loading. I also ran some torsional scenarios. Round tube is stiffer again by a fair amount and overall peak stresses are less for the round tube.

The helix tube began to show points of failure at 1.5 times a factor of safety and the round at 1.75. The round tube is superior here also.

I would say though, taking a queue from Mythbusters........This myth is BUSTED....

I do not believe your model is accurate to the shape of the tubing that lynskey uses in the pro 29. if you look closely you can see within each segment of the helix there are large radii . So what your looking at is a regular round tube twisted and then in between each twist the tube being pushed inward ... creating a strong inner radius. i may be wrong but it seems like your model is a square tube twisted ?