leovendramini wrote:In my mental image,only the 2 bottom holes are necessary as there would be only one lengthening option.70mm would be total length and comp. riders would have no use for it as their cranks are dedicated anyway.These would be for the non pro who just wants some extra mechanical advantage.Had the design in fig 2 dispensed with all those options it could have been a success.Thanks for the post.
That's going to be some pretty coarse adjustment though. I think that incredibly few riders would want anything even remotely like the thing pictured bolted onto their cranks.
As for "extra mechanical advantage", that's what gears are for. You can use either a smaller chainring or larger rear sprockets to get greater mechanical advantage. Having the optimal length cranks for your height (or more specifically your leg length) can increase your bio mechanical efficiency, but it's not really about mechanical advantage (as that can more easily be obtained in other ways).
Longer cranks put your knee joints though a greater range of angles. Up to a point that's ok, but you can definitely go too far and then you lose both comfort and efficiency. It really isn't just as simple as the larger the better.