152 mm cranks is like adding a bigger chainring

[hillslayer@]

Was doing a lot of ghost pedaling on climbs that where in the 7% range with my mid drive hub combo and 46t was as big as would fit do to chainstay design so put some 152 mm cranks on and now gearing seems perfect. I am putting these on all my bikes.

 

[ebike4healthandfitness]

Yes, one of the benefits of shorter cranks is that it can make a bike with too short of gearing operate as one with gearing that is more ideal. For bikes with max size chainrings but still too short gearing (e.g. small diameter tire bikes) this can also help avoid the use of 10T or 9T cogs which are less efficient than 11T cogs. Then there is also a possible aerodynamic benefit to using the shorter cranks:

The Benefits of Reducing Your Crank Length

Shortening your crank length can have some major benefits in terms of speed, aerodynamics, power, and comfort. Here's a deep dive into the subject.

www.trainingpeaks.com

"Going to a shorter crank will allow you to ride at a lower back angle which minimizes frontal surface area improving aerodynamics."

This benefit applicable even to recumbents:

9 Reasons to Upgrade to Short Cranks

If you want maximal power when climbing or sprinting, there is no crank length better than 145mm. If you need more reasons to upgrade, keep reading. Below are nine reasons why you should upgrade to short cranks. Many of these benefits also apply to standard (legacy) bicycles, not just your...

cruzbike.com

"Short crank arms make the bike more aerodynamic (they actually make the RIDER more aerodynamic on the bike).
With shorter cranks, your knees don’t pop-up as far into the clean airflow, nor do your heels drop as low into clean airflow; thus reducing turbulence and drag."

Another benefit as you mentioned is the reduction in the amount of ghost pedaling with your bafang mid drive. This because, for one reason, you are trading torque for rpms with the short cranks and this meshes better with the high Kv of the BBSHD.

 

[neptronix]

For me.. they hurt my legs when i actually pedal, which is all the time, and i also put out crappy power.
All experiments for me have lead me right back to the 175mm crank.

 

[hillslayer@]

Rode 20 miles today tomorrow doing 80 miles, so if they cause a problem will find out then.

 

[neptronix]

I think it doesn't matter because you're ghost pedaling.... not applying force

 

[Chalo]

I used 152mm cranks on my BBS02 so I could pedal usefully up to the motor's efficiency peak. When I switched that bike to a hub motor, I switched to 215mm cranks. Then I switched to a smaller rear wheel and I put on 185mm cranks for better ground clearance.

They all work for me, but when I'm the prime mover, I prefer long cranks.