Best front chain ring size for max speed on 20" BBSHD ebike

djneils98

New Member
Region
United Kingdom
So I have a Tern Verge D9 that I've put a BBSHD on.
Currently I have a 52T chainring on the front.
The smallest rear cog is 11T but currently the bike gets max speed in a higher rear cog.
Would I get any increase in max speed by going for a smaller front chain ring (say 44T or 46T) and utilising the 11T rear or will it not really matter?
 

JRA

Well-Known Member
It doesn't really make any sense that you are getting a higher speed in other than the 52-11? Certainly lowering your chainring size isn't going to help.
 

djneils98

New Member
Region
United Kingdom
It doesn't really make any sense that you are getting a higher speed in other than the 52-11? Certainly lowering your chainring size isn't going to help.
I think the motor just doesn't have the power/torque to hit it's max cadence on 52-11
 

djneils98

New Member
Region
United Kingdom
then shift the gear? :oops:
I don't think you understand what I am asking.
At max throttle the bike hits about 32mph when I have the rear gear on the 13T cog.
Dropping down to the 11T one does not increase the speed. If anything the bikes slows down slightly.
I just wondered if dropping the front cog size would change anything - I think the BBSHD wants to spin at about 160 RPM flat out.
 

mschwett

Well-Known Member
Region
USA
So I have a Tern Verge D9 that I've put a BBSHD on.
Currently I have a 52T chainring on the front.
The smallest rear cog is 11T but currently the bike gets max speed in a higher rear cog.
Would I get any increase in max speed by going for a smaller front chain ring (say 44T or 46T) and utilising the 11T rear or will it not really matter?
the mid-drive motor doesn’t care if it’s a 48 in the front and a 24 in the back or a 24 in the front and 12 in the back - it’s entirely about the ratio between the two. the only situation where changing the front might help if you can’t reach max speed on 52-11 is if the jumps are so big between rear cogs (say the next one is a 14) that the smaller front ring gets you to an in-between sweet spot. highly, highly unlikely!