It seems pretty reasonable to assume that a pedal based power meter would work fine on an E-bike but has anyone ever tried/proved that crank arm power meters work on mid-motored e-bikes?
The reason I ask is that I have an emtb (that I cannot access the internal power/torque data) and I don’t want to clip in but I’d like to have a power meter as I often ride with my wife and it can be quite relaxed so I’d like to be able to maintain either Z2 or maybe even target certain power on the climbs etc.
I’m sure this seems a bit of an odd question but I couldn’t find anything on google about it. I’m a noob so I don’t fully understand how crank power meters work but I assume they can isolate the effort from the rider and motor.
I have a HRM and always use that, in case anyone suggests this as an alternative.
Alex - I did some research on this several months ago and found no data or experience with power meters on the web. I have a set of Assioma power meters on a road e-bike and a set of Garmin rally 200s on an e-mtb. I find the setups work very well for outside structured workouts, turning off or down the e-bike motor during intervals allows me not to blow up on some relatively steep climbing rides. It remains unclear how accurate these setups are because I have no way to compare the output being measured. The power output by me and the motor are reported separately on my Trek fuel exe LCD display but is wildly inaccurate c/w what is reported by the Garmin pedal meters. I could find no reported experiences with crank-based PMs and e-bikes. Hope this helps. - jke
The physics of how a crank arm power meter works remain the same regardless of e-power added (mid or hub drive doesn’t make a difference).
The power meter detects the deflection in the actual crank arm to calculate the force,
Then it adds the RPM (velocity) to estimate the power (left side doubled).
So you will get the power data from the LS PM that is your actual power, regardless of e-bike assistance. Think of the e-bike assistance like a tail wind, that gives you more motion but the effort you put into the crank remains the same system, even if you get a “boost”.
I have an eMTB that reports both total power and the power I am generating, so I don’t need power pedals, but having said that, if you’re just doing mostly Z2 rides, I would just use my HRM and save the money.
We don’t necessarily do Z2 rides but waiting for the wife, and/or using the assist can mean that my HR drops out of the training zone. I could probably maintain a more consistent workout if I knew how much power I was using. Then of course we do some pretty serious climbs so I could use the power meter to stay in whatever zone I was targeting, whether that was VO2 or Zone 2.
Mostly I’m absolutely happy to use the HRM but I’d like to do some outside rides that I can record in TR.
Long shot here - and probably on the expensive side. I’m not overly familiar with eMTB drivetrains, but would it be possible to replace the left crank with something that is compatible with the 4iiii factory install? Not sure what motor you have, but as an example it looks like you can get a left FSA crank for a Bosch Performance Line motor, and 4iiii do deal with FSA cranks.
That’s the point though, having power means I can change the assist and gearing to keep it nice and constant, which is almost impossible on normal MTB riding. Also it means doing the same on the climbs to do intervals.