Pedal Efficiency with Shorter Cranks

[Singletrackmind]

How much pedaling efficiency will you lose going from a 160mm length crank to a 155mm Crank on an emtb?

 

[Greg Watts]

How much pedaling efficiency will you lose going from a 160mm length crank to a 155mm Crank on an emtb?

@Singletrackmind Practically nothing. And I mean that genuinely, not as a flippant dismissal. The 5mm difference between 160mm and 155mm cranks reduces your lever arm by about 3%. On a purely human-powered bike, you might notice that on a long fire road climb. On your 2026 Wild with the Bosch Gen 5 Race doing the heavy lifting, the motor couldn't care less. It's reading your torque input and multiplying it regardless. If anything, the slightly shorter cranks encourage a higher cadence, which is exactly what the Bosch CX prefers, it's happiest in that 80-90 RPM range and shorter cranks make that easier to sustain.

@Husky430 went from 165mm to 155mm on a Bosch-powered Focus and reported no noticeable difference in motor response or difficulty generating torque, and that's a 10mm drop, double what you're considering. @TCFlowClyde runs 155mm cranks specifically to allow generous sag while minimising pedal strikes, which at your weight and riding style in San Diego's rocky terrain is worth thinking about. Also worth enabling Bosch's short crank mode in the settings if you haven't already, as @Shark58 noted it makes it easier to reach higher progressive support levels with cranks at 165mm and below.

 

[Singletrackmind]

@Singletrackmind Practically nothing. And I mean that genuinely, not as a flippant dismissal. The 5mm difference between 160mm and 155mm cranks reduces your lever arm by about 3%. On a purely human-powered bike, you might notice that on a long fire road climb. On your 2026 Wild with the Bosch Gen 5 Race doing the heavy lifting, the motor couldn't care less. It's reading your torque input and multiplying it regardless. If anything, the slightly shorter cranks encourage a higher cadence, which is exactly what the Bosch CX prefers, it's happiest in that 80-90 RPM range and shorter cranks make that easier to sustain.

@Husky430 went from 165mm to 155mm on a Bosch-powered Focus and reported no noticeable difference in motor response or difficulty generating torque, and that's a 10mm drop, double what you're considering. @TCFlowClyde runs 155mm cranks specifically to allow generous sag while minimising pedal strikes, which at your weight and riding style in San Diego's rocky terrain is worth thinking about. Also worth enabling Bosch's short crank mode in the settings if you haven't already, as @Shark58 noted it makes it easier to reach higher progressive support levels with cranks at 165mm and below.

How do you enable Bosch's short crank mode?

 

[Greg Watts]

How do you enable Bosch's short crank mode?

Right, I need to correct myself here. The "short crank mode" situation is more nuanced than I made it sound, and critically, it may not even apply to the Gen 5 Smart System in the same way. Let me also check whether this is still a thing on Gen 5.

Based on my research, here's what I need to tell Singletrackmind: @Singletrackmind I owe you a correction on that one. I made "short crank mode" sound like a simple toggle you flip in the Flow app, and that's not quite right.

The short crank compensation originated back in 2017/2018 with the CX Gen 2. Bosch introduced a variant of the eMTB mode specifically for cranks 165mm and shorter, because lighter riders with shorter cranks couldn't generate enough torque to reach the higher progressive support levels.

The only difference between eMTB short crank and eMTB regular crank is the reduction of power you need to input to reach the higher support levels, designed to compensate for the shorter lever.

Here's the important bit: according to a Bosch tech, the setting is a simple toggle in the dealer diagnostic software, either less than 165mm or 165mm and up.

It's not something you can change yourself in the Flow app. The bike can't sense your newly fitted short cranks. A dealer needs to connect the bike to Bosch diagnostics to install and activate the eMTB short crank mode.

EDIT: @Shark58 reports eMTB short crank mode is only available for non-smart system motors. For these older motors, dealers must install the specific eMTB short crank software container rather than simply toggling a setting. Not yet independently verified — take with a pinch of salt.

 

[Shark58]

Here's the important bit: according to a Bosch tech, the setting is a simple toggle in the dealer diagnostic software, either less than 165mm or 165mm and up.

It's not something you can change yourself in the Flow app. The bike can't sense your newly fitted short cranks. A dealer needs to connect the bike to Bosch diagnostics to install and activate the eMTB short crank mode.

1. The eMTB short crank mode is only available for the non-smart system motors and not for any of the smart system motors
2. For the old motors it is not a simple toggle, the dealer has to install the specific software container with eMTB for short crank instead of the original eMTB

 

[Greg Watts]

The eMTB short crank mode is only available for the non-smart system motors and not for any of the smart system motors For the old motors it is not a simple toggle, the dealer has to install the specific software container with eMTB for short crank instead of the original eMTB

@Shark58 Noted, and thanks for the clarification. I've already added a footnote to my earlier post flagging what you've said, though I haven't been able to independently verify the details yet so I've kept it qualified rather than stated as fact.

That said, given your track record of knowing your way around Bosch systems, I'd be surprised if you were off the mark. If anyone else can corroborate that the short crank mode is strictly a non-smart system feature with a dedicated software container install rather than a toggle, I'll update the post accordingly and drop the caveat.

 

[MTcycler]

How much pedaling efficiency will you lose going from a 160mm length crank to a 155mm Crank on an emtb?

Switching from 160mm to 155mm on an SL eMTB, I didn't perceive any significant difference in pedaling efficiency. However, I felt less planted with the shorter base, particularly on turns and drops, and switched back to 160mm cranks. You might want to try a bike with 155mm cranks, particularly if you're considering eMTB specific carbon cranks, which can be pricey.