Newbie question Problem with 8fun 250w mid drive

[Derek M Walshaw]

Hi all. My first post. I have a 8fun 250w 36v mid drive on my MTB. When moving off it's started to judder until I get the crank turning. Once moving it seems ok, The more assist I have to set off the worse the juddering. Also noticed the watt meter jumps between showing power then zero power until the crank has a decent cadence. Any Help appreciated
Thanks

 

[Kinninvie]

Are you setting off in a low gear.
It will judder if the gear is too high.

 

[trex]

make sure that the motor is properly in place and the top of the motor housing should touch the downtube so it does not rotate around the BB when it starts.

 

[Derek M Walshaw]

Are you setting off in a low gear.
It will judder if the gear is too high.

The gearing is a 1 x 8. Even using the rear big cog it still judders. Again the more assist the worse the juddering. Using just the thumb throttle to move off, there is no judder at all. Also there's no judder using the pedal assist. Could it be the crank sensor, what ever that is?
Also what the best size front ring. I will be using the bike off road and where I live it's very hilly
Thanks for the replys

 

[Kinninvie]

Sounds like an internal problem.
Is the motor under guarantee\?
I currently us a 44T front cog which is the smallest standard one.
I have just bought an adaptor and 38T one for offroad riding which I think will be perfect.
http://www.ebikecomponents.eu/webshop/parts/bafang-bbs01-bbs02-parts/detail/257/bafang-chainring-adapter-.html

 

[Derek M Walshaw]

Sounds like an internal problem.
Is the motor under guarantee\?
I currently us a 44T front cog which is the smallest standard one.
I have just bought an adaptor and 38T one for offroad riding which I think will be perfect.
http://www.ebikecomponents.eu/webshop/parts/bafang-bbs01-bbs02-parts/detail/257/bafang-chainring-adapter-.html

Thanks for the advice. As I will be using it mostly off road I was looking at getting a 42t ring. I know top end speed will be sacrificed. Will there be more bottom end torque ?
Cheers

 

[Geebee]

Thanks for the advice. As I will be using it mostly off road I was looking at getting a 42t ring. I know top end speed will be sacrificed. Will there be more bottom end torque ?
Cheers

Yep more torque at the rear wheel, if you are doing serious off road I would do what Kinninvie is and get an adapter to allow smaller rings, it would also allow cheaper and easier ring swapping.
I use a 46 to 11-32 with a drive 20" wheel and the gear inch would be perfect for off road with a BBS01, mine is for steep on road but I have health issues that limit pedalling power.
On a European forum one rider had gone down to a 32 tooth on his MTB due to extreme off road hills.
Bear in mind Kinninvie's is a BBS02 (3x the rated wattage).

I just calculated and my gearing would be equivalent to 32 tooth rear and a 32 tooth up front on a 26" wheel MTB, that was a surprise

The higher the cadence/motor speed the less heat generated and the greater range.