found this info -
I have the following presumption:
First of all chain ring is a part of Bafang Ultra motor kit. first this kit was delivered with a 44t chain ring by Bafang (I took the original Bafang 44t chain ring of my AM1000 motor for my EX). now it seems to be a 40t chain ring.
Bafang Ultra motor runs best & cooler at high rpms and low torque (low amperes) - resulting to the same wattage as low rpms and high torque. in fact you will kill your Bafang motor and/or it gets very hot when using low rpms and high torque (also applies to Bafang BBSHD motor - where the plastic gear just melts - but Ultra motor has no plastic gear -anymore- !).
If I would be a manufacturer and I would have returns with problems caused by that - what would I do ? = yep, I would provide a smaller chain ringproblem solved. benefit would be lower temperatures and a longer motor lifespan which is not a bad thing at all.
of course it is not nice if you have to ride your Bafang motor at 11 teeth cog and 35 km/h or 20 miles/hour at highest possible rpm giving by the voltage and your human speed of being able to pedal the crank… when you are not offroad.
my solution: I use larger chain rings (44t with Frey EX and 50t with Frey AM) but also higher voltages with my own built batteries (up to 80 volts). right now I am building the 2 new batteries for my Frey EX. my Frey AM1000 is btw problem free with this large chain ring since around 3500-4000km. of course I take care of the right gear at hills etc. without my personal care of choosing the right low gear, yes, I would have destroyed or damaged the motor...
but of course this is not the solution for everyone…
only a presumption…
anyways, yes, you can change it to a nice 44t Wolftooth or RaceFace 130 BCD chainring.
I have the AM1000 with the SRAM EX-1 gear set. Since the chain is wider would the chainring matter? I am looking to go to a 44- 46 tooth chainring. Which would work for my set up? Thanks