Titanium vs aluminum?

[ian.stockwell]

The elastic or Young's mudulii (?) for the three materials being discussed will vary slightly according to the alloys but they are roughly:

Aluminium 70GPa
Titanium 110GPa
Steel 205GPa

So for a tube of the same size aluminium will deflect or flex 3 times as much as the steel one under the same load.
ali bike frames are stiff because of the tube sizes are so much bigger than steel, double the diameter of a tube and its stiffness will increase by 16 times (I think) easily overcoming the fact that the material is more flexible.

[Niko]

Thank you for those interesting replies. It's good to hear some well founded arguments instead of just speculating.

Would a heavily ovalized tubing be an option for Ti unicycle frames (increasing stiffness at least in some directions)? The whole tubing diameter can't be increased by much.

[johnfoss]

Originally Posted by Niko

Would a heavily ovalized tubing be an option for Ti unicycle frames (increasing stiffness at least in some directions)? The whole tubing diameter can't be increased by much.

I don't know if ovalizing helps any against twisting (torsion?). It probably helps some, but perhaps not enough to justify a higher cost in materials or build?

The second axis of force through a unicycle frame is probably stress from pushing-pulling on the seat or handle. This would tend to bend the frame to the front or rear, starting from wherever the bottom of the seat post is inside the frame. That's another reason why you want a comfortable amount of tube inside the frame...