Speed:Assist calibration error - cuts out 10% under limit

[Beertaco McMountainbike]

The pedal assist cuts out at 23 not 25kmh and that sucks. I’ve noticed that my Garmin GPS is reading about 23km/h when the readout on the Purion shows 26kph and assist cuts out and the dreaded Bosch resistance (feels like a spin bike friction brake applied at low/mid pressure) kicks in. It’s bad enough it cuts out under the limit but the resistance is really unacceptable. I had a Bosch CX 5 years ago and the resistance was minimal and could comfortably ride fast pace over assist speed limit, nothing like this bike.
Anyone else had this on Powerfly?
Is there a remedy that doesn’t require the proprietary software?
How is it recalibrated in field? Please note I would take it to my Trek dealer but they are 3200km away in Adelaide or Perth.
I love the bike but don’t like this speed tax.

 

[thewildblue]

Try moving the magnet position on the rear wheel. Might make a difference.

 

[Beertaco McMountainbike]

Nope but thanks for the idea (which I had previously tried). Moved further and tested but no impact. I suspect the magnet sensor has a wide field but motor output not calibrated on the magnetic field range. It’s gotta be in the software. Today sitting steady on 25kph on Garmin and reading 26.5 on Purion. And then “the wall”.

 

[Lad]

It is in the software - most likely the wheel diameter is not set right.

I had a long chat with a head mechanic of Thok MIG bikes in Brisbane. We were talking about his willingness to change wheel sizes or even put on different tyres if I order the bike from him and he said he will re-program the system for free.

He said not many people realise that when they mount different size tyre, they will in certain cases find that their bike cuts off before 26km/h limit. He gave me and example between some Maxxis and Schwalbes (forgot the details) that caused to cut motor off at 23km/h. I was quite surprised when he said he knows only three other bike mechanics Australia wide that will go and re-program the drive unit (Shimano Steps) according to the type of tyre/wheelset combo.

I know your Trek is a Bosch, but it should work on the same principle.