Here is my take on crank length. I don't think crank length matters much except for triathlon or tt-ing. The difference between 170 and 175 is about 3%. Such a change is easily within the normal range of motion limits of the joints so should not account for much of a mechanical leverage difference in the legs or joints. Only when the cranks get way too long or way to short should this be much of a problem for most people.

What seems to matter most from an overall efficiency point of view is pedal speed. To keep pedal speed the same if we change crank length 3% would simply require changing the cadence 3% or changing a 75 cadence to 77.25 or 72.75 (depending upon whether you went shorter or longer respectively). This is hardly a problem to deal with in racing as the difference between a 14 and 15 tooth cog is over 6%.

So, we see shorter cranks provide almost zero "leverage" difficulties and even if we went very short this could be easily be made up for by different gearing to keep pedal speed the same for the same power. So, there is nothing lost in climbing by going to shorter cranks if we gear the bike appropriately. But, shorter cranks offer other advantages.

1. It will take less energy to make them go around one revolution as the up and down excursion of the thigh is less by twice the crank length difference. This means one can achieve higher rpm for the same energy expenditure so one is less likely to "spin out" on the down hills. So, higher top end speed on the downhills.

2. The lesser thigh excursion means that we will be less cramped when we are in the aero position. This should allow the rider to either generate more power in their aero position or get lower without losing any or much power. So, higher speed on the flats.

Any or all of these differences should allow the cyclist to race better.

The only question for me is how short is too short? It is why I have recently extended the adjustability range of our basic PowerCranks to go as short as 155 to allow the user of any size to experiement with this some.