Originally Posted by
Salubrious
Even cranks 100 years old do not have that kind of variance. Ask me how I know.
The issue here is torque of course- and with longer cranks you have more torque. But since the issue is torque, how much torque can your knees handle before they cause you to stop riding? When you run shorter cranks, its easier to spin faster, so when confronted with a headwind or hill you might have to gear down a bit. I've gone from 175s to 170s and not found that I had to mess with the gearing on the bike. If you went to 155s its likely a different matter.
I was being deliberately hyperbolic to make a point, and you just helped me.
I have five single bikes, four tandems and two recumbents. There is every length of crank on them from 165 through 175 and I couldn't tell you what has what. It is simply a non-issue, that small a change. Well, if it isn't costing anything, why not. But to remove a perfectly fine set of 170mm cranks. Pay ... what, $100? $150? More? You'd better, if you want something decent. Or find them used. Now, can you make the swap yourself or do you have to $$$ to have it done by the LBS? For 5mm? I don't think so. That is all I'm saying and all I ever will say about it. A 3% change just isn't worth three figures to try out.
We have a
double recumbent tandem built for Dutch people. At 5'10" I can 'just' reach the pedals with the 170's that are in the Captains spot. At 5'6" my wife can 'just' reach her pedals. There isn't any way to fix that. Theoretically my wife should be alright but she would like some shorter cranks. The rule is "the Stoker is always right" so I am duty bound to make it right for her. I'm pretty sure her cranks are 170's just like mine. Taking my own medicine, I am not going to swap a full out tandem crankset. I will find some
crank shorteners. Happiness begins at 155mm. Go big, or go home. YMMV.