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I've been trying to help, but you don't seem to be taking the hint.
Hey I'm just curious and trying to gather information. Nothing personal.
Of course the outside diameter of the spindle is only a very small part of the story. I just found some deflection data that seem to confirm my feelings :)
@danstuff, agreed.
Jaap-
Nothing personal
Ditto, I just thought I'd try to limit your embarrassment by being more explicit, since you keep claiming that 30mm aluminium is noticeably stiffer than 24mm steel
found some deflection data that seem to confirm my feelings
Yes, data which confirms our bias is the best kind. Best to ignore any which doesn't :)
gbj_tester
There's a lot of difference between left and right cranks besides the tube joining them together in the middle. If you want to know how much the spindle winds up when driven by the left crank, you need to measure the spindle wind up, not the total deflection of everything in the load path from chain to pedal bearing.
I've been trying to help, but you don't seem to be taking the hint. Steel is about 2.5 times as stiff as aluminium. A 24mm tube with 2.5mm walls (HT2, pilot bore for M20×1.0 bolt) is about 0.4 times as stiff as 30mm tube with 3.5mm walls (BB30, pilot bore for M24×1.0 bolt) if the material stays the same. I think you can see where this is going (0.4×2.5=?)
The advantage of aluminium 30mm over 24mm steel isn't that it's stiffer, it's that its about 60% of the mass and uses bigger bearings.