Bosch Performance motor "surging"

#1
I recently purchased a Trek Super Commuter 8s with the Bosch Performance motor. I live in a very hilly area and I've been riding it every day. No problems at all, very natural feel. Today I tried a much stepper hill and ended up in the lowest gear on the cassette and in Turbo on the motor. I currently have 125 miles on the bike. At first it was fine but it started surging. I wasn't able to maintain a steady cadence, and if I paused in pedaling, the motor would continue to pull. Then, when I would begin pedaling again, the motor would lag initially before surging again. Once I cleared the hill, it continued this behavior in a number of gear and motor combinations. I immediately took it to my dealer and they said they put it through a diagnostic test. It showed no errors. It feels, to me, like an issue with the pedal sensor.

Any suggestions?
 

slomoshun

Active Member
#2
This may, or may not apply to your situation, but it's worth mentioning. We all have a dominant hand, and leg, which is stronger than the other. You may unconsciously be applying more force with your strong leg which will cause a surge.
 

rich c

Well-Known Member
#3
Not sure Bosch uses a traditional pedal sensor. It will be inside the motor case and I would be surprised that if it has a problem, it didn't show up on the diagnostic. I climb two hills on my usual route. Both require lowest gear and turbo setting. Ride them about 5 days a week. Never had that problem.
 
#4
The other thing is, following that hill, I returned to a portion of my normal ride and the problem continued through that.

When I stopped to push a crosswalk button, the bike pulled forward a couple of extra feet.

On every ride, in every situation before, it felt like the motor responded to me. In other words, I supplied input and the motor responded. Now it feels as if it is trying to get ahead of me. Several times, the bike acted as if self propelled.
 
#5
I've ridden 60 miles since I picked up the bike following the shop trip. Only thing I can figure is that either the bike experienced a (hopefully) one-time error or the combination of the very steep hill and my lack of strength created a situation where the bike was confused. Either way, it's working fine now. Both Bosch and Trek were very helpful and patient.

Love the bike.