Advice on gearing with 2011 Kalkhoff Agattu requested!

[Gregorio]

I have just purchased a new Agattu which has a 19T rear sprocket running an 8 speed Nexus hub. It has a 35T front sprocket and I gather it has a 9 tooth motor drive sprocket. I doubt I will change the gearing but after having read a few postings by Flecc I would be interested to know what the effect (if any) would be of fitting a 17 or 18T rear sprocket and an 11 tooth motor drive sprocket.

 

[flecc]

The 18 tooth would be too small a change to be worthwhile, but the 17 tooth rear sprocket would lift the assist limit from 15 mph to almost 17 mph.

Alternatively, leaving the rear sprocket at 19 teeth but using the 11 tooth motor sprocket would raise the assist limit from 15 to just over 18 mph.

The most useful factor in changing the motor sprocket is for increasing the cadence (pedal spin speed) to suit the more sporting rider. To do this, the 11 tooth motor sprocket is used and the rear sprocket increased to 23 teeth, which leaves the assist at the legal 15 mph limit but increases the cadence by 22%.

If opting for a higher assist speed, bear in mind this reduces the range since the motor is working over a greater range of road speeds.

 

[Gregorio]

Many thanks for your helpful input-much appreciated.

The idea of having a 23 T sprocket at the back is attractive with an 11 tooth motor sprocket. I suspect a longer chain will be needed, but most bike shops should be able to deal with this.

Am I correct in thinking that the 11 tooth sprocket may result in a loss of torque? I don't live in a hilly area but there are a few?

 

[flecc]

There's no loss of torque if you compensate with the 23 tooth rear sprocket Gregorio, the ratio of motor revs to rear wheel revs remains the same.