I’ve ridden various sized unis on cranks down to 75 mm but try as I might I can’t get comfortable on my 36 on 125s. I can ride it for miles, but I never have the same confidence as on 150s.
As a general rule I find that if you can idle, there is no speed and control advantage to riding on cranks shorter than you can comfortably idle with.
Yes, that was my reason for the question - big leap between sizes. I can not just try them - I have to grow my “home inventory” of spares 
Thank you for advice, I will order 125s and try them in action.
Awesome… I have to learn idle first… All my tries failed - just can’t get how to do that but I keep on learning.
145s are comfy for now but I want to try something more (I bet you know that feeling 
).
Thank you very much!
How short is too short…well, if it feels too short then it probably is 
I dropped from 165’s to 137’s the other day while riding single track. I was able to do it, but it was wierd, I loss all of my torque and had to rely solely on momentum. Balance wise it was not all that different, same wheel, high seat position, easier spin, but it was not as controlled and ultimately I switched back to the 165’s for the rest of the ride.
I’m contemplating 150’s for this weekend, just to see if my increased experience on the 36er has grown my skill enough to manage off road on shorter cranks. My reason for reducing crank length is not efficiency, but an effort to smooth out my spin when riding through turns on single track; I seek the flow 
As to riding 114’s on a 36er, sure, it could be done, but I’d want to ride something smaller than 145’s before dropping to such a short crank. It’s not that the total decrease is such a big deal (165 to 137 is the same reduction) but having so little leverage on such a big wheel would require a very fine sense of balance that can only come from some short crank experience.
See if you get some used Moments 150/125, that would be a nice way to switch back and forth depnding on where you’re riding.
Now I really think that I will not be able to move 36er with 114s because of momentum lack
Actually I planning to purchase 127/150 Spirit for my 26er and I think that putting them on 36er will be more rational then buying another 125s…
This is really hard to find used parts with shipping to KZ 
No, I have to stop first, lol! But yes, I change to 110’s for the ride back down.
Terry, you change cranks on the side of the road before riding back down, really?
I’m not saying it’s impossible, but I’m pretty fast at swapping cranks, and even on a stand it takes fifteen minutes, more like twenty on the side of the road; been there, done that.
You’d better off with dual position cranks.
With square taper cranks and all my tools readly available, it’s a 5 minute job to change cranks. 10 minutes including getting out and clearing away the tools. With splined, it’s slightly faster.
Moving the pedals from one hole to the other on dual-length cranks takes about 1/3 as long, assuming that the hole isn’t full of mud and grit from your ride.
To carry on with the off topic discussion… 
Guess I’m in the opposite mind camp from Terry on this. I’ve always ridden double hole cranks on my 29er, have never changed holes during a ride, and doubt I ever will. I’ve also settled on 152 cranks for my Coker, and never change them - they work OK both in and off road but probably not the “best” for either. Changing stuff around is a PITA, and adds risk if something going wrong (stripped threads etc.). Not to mention having to carry extra stuff. I prefer to just pick the best overall setup and ride.
Of course, I’ve ridden waaay less than Terry, and admittedly at a different level, so maybe it’s just because I’m not to the point of wanting to maximize performance.
-James