Panasonic 1t motor sprocket clarification

[andyh2]

I'm sure I've read in an 11t motor sprocket thread that swapping from the 9t to an 11t gives a proportional decrease in power output, but I don't understand how that can be the case. I've written my understanding below. Am I missing something?

Panasonic system gives power according to;
1. Which mode it is in high, med or low.

2. Rider input to pedals through torque sensor.

3. Cadence. But it doesn't actually measure cadence rather it measures motor speed, which is directly proportional to cadence. The actual proportion being determined by the motor sprocket size with 9t as standard.

With 9t max power output is at a cadence of 39 RPM and it reduces to cut off at 60 RPM cadence.

Swapping for 11t will move max power output and final cut off point up the cadence RPM by 11/9. ie max output at 48RPM tailing off to cut off at 73RPM.

If the top gear of the bike remains the same then this will result in an increase in the speed at which motor will assist. ie up from around 15mph to 18mph.

Complete legality could be restored by reducing top gear, but would result in reduced ability to ride above assist speeds.

I take it it's the motor assistance at higher speeds which reduces battery range as it does when changing the gearing to higher than standard?

I don't see how the power of the motor is affected other than as stated above.

 

[andyh2]

Er.....that should be Panasonic 11t motor sprocket, but I can't edit the title!

 

[flecc]

It doesn't cut the power, but it does shift the power amounts in relation to road speed. It gives you higher amounts of power at any given road speed between 9.4 and 18 mph since it shifts upwards the power phase down slope.

The range loss is as you've said.

 

[andyh2]

Would that power increase / range reduction be same if the rear sprocket was reduced by the same ratio?

I can see how battery range would be affected quite severely as 9.4mph to 18mph is right where the majority of riding is likely to be done.

It'll never happen as it would be open to abuse, but if we could input the cadence range we like and the gearing we're using, with the system adjusting the power output to suit, but keep legal it'd be great.

I expect they put quite a lot of thought into balancing the range and power and of course we only get to change either max gearing or motor sprocket but without being able to make the other changes which would maintain the balance between power output and range.

Bit like the Bank of England setting interest rates and money supply, but not having control of all the economic subtleties!

 

[flecc]

Yes, the rear sprocket change alone would have the same result.

As you've guessed, the balance chosen by Panasonic is a very clever one, squeezing out the maximum range with acceptable motor power within the legal speed range. Any change loses out in at least one way.

 

[andyh2]

Thanks Flecc, much appreciated.