Front or Rear Cog Change?

[lemmy]

Spring time comning up and I fancy a bit of messing about...

Reading through Flecc's highly clear and informative web pages, it would seem interesting to change the gearing on my 8 speed hub geared Kalkhoff.

The best bet seems to change to 9 tooth front motor cog for an 11 tooth rather than the rear 23 for an 18 or 19. I say this partly because the increased cadence would put me closer to what I am used to on my non-powered bike as well as up the gearing a bit.

Has anyone done this and can give practical observations on the effects on rideability and range?

 

[Polar753]

If you can find a front one could you let me know where you got it from.

I'm looking to do the same.

I have changed the rear to the smallest, 16 I think. assist is now up to about 21ish, you can keep peddling until 30 or so. Climbing 10% hills you are down to 2nd at approx 7-8mph medium effort. Overall I think its better but the bike doesn't feel quite so lively, but it obviously depends on the type of cyclist you are. I like to pedal all the time so found the standard gearing a bit frustrating forcing me to freewheel on every downhill. I would recommend giving it a go as its not expensive and reasonably easy to do. I'm sure lots of others have much more detail. I find the range has now dropped to probably less than 20 miles i'm in a reasonably hilly area.

Thanks.

 

[flecc]

A few have changed to the 11 tooth sprocket Lemmy so hopefully they'll give their impressions. The range will probably drop by around 15% whether you change sprockets at the front or rear, since power will be used over a wider range of road speeds.

This varies quite a lot with rider input ability of course. If the higher gearing leads to more use of the high power mode as could happen with a less strong rider, the loss of range will naturally be greater.
.

 

[flecc]

Polar, the 11 tooth sprocket is available because it's the standard one on the "S" high speed version of the Panasonic unit.

The "S" bikes that use this are made by Kalkhoff and BikeTech, so if Kalkhoff agent 50cycles don't hare them at the moment, try the UK BikeTech agent, Vita Electric. It appears their website has currently been hacked by Electric Bikes Direct, so phone or email:

email: mckeownace@aol.com

Phone: 020 7794 3373

Tell them you need an 11 tooth motor sprocket from the THS or S series Flyer bikes and ask if they have one in stock.

Another agent for Flyer models is Bicicletta Limited in London, so worth a try. Here's their contact page

Otherwise you could try a German agent on the off chance there's an English language communicator there. Here's one in Hamburg:

E-bike Store Contact Page
.

 

[Polar753]

Polar, the 11 tooth sprocket is available because it's the standard one on the "S" high speed version of the Panasonic unit.

The "S" bikes that use this are made by Kalkhoff and BikeTech, so if Kalkhoff agent 50cycles don't hare them at the moment, try the UK BikeTech agent, Vita Electric. It appears their website has currently been hacked by Electric Bikes Direct, so phone or email:

email: mckeownace@aol.com

Phone: 020 7794 3373

Tell them you need an 11 tooth motor sprocket from the THS or S series Flyer bikes and ask if they have one in stock.

Another agent for Flyer models is Bicicletta Limited in London, so worth a try. Here's their contact page

Otherwise you could try a German agent on the off chance there's an English language communicator there. Here's one in Hamburg:

E-bike Store Contact Page
.

Thanks flecc, I'll get onto that tomorrow.

 

[lemmy]

I'm being thick here but I'd appreciate a little guidance.

Changing the front cog from 9t to 11t will leave the gearing the same but raise the power band it seems to me. Is that correct?

But presumably, since the chainwheel and rear sprocket stay the same, for any given speed and gear the cadence will remain the same?

So if the cadence is 40 at 15mph with 20% power assistance, with the 11t cog the cadence will remain 40 at 15mph but the power assistance will be 40%, all these being illiustrative rather than actual figures, of course.

As far as I can tell, 50Cycles have the 11t cog in stock, by the way.

 

[lemmy]

Still trying to raise this query. Any thoughts, any kind person?

 

[Straylight]

From what I understand, you're correct that the gear ratios for your actual pedalling will remain the same, and that changing the motor sprocket will simply change the amount of work that the motor's doing for a given cadence.

As I believe that the panasonic system uses a special freewheeling chain-ring to allow you to back pedal, it seems to me that your easiest option for altering your cadence for a given speed would be to change the sprocket at the hub gear, smaller to reduce cadence, larger to increase.

Hope this helps

 

[flecc]

So if the cadence is 40 at 15mph with 20% power assistance, with the 11t cog the cadence will remain 40 at 15mph but the power assistance will be 40%, all these being illiustrative rather than actual figures, of course.

That's it. The cadence at a given road speed is set by the chainring size and rear sprocket for the gear in use and these are not being changed.

The 11 tooth motor sprocket substituting for the 9 tooth must therefore run slower by the percentage difference in those sizes for the same chain length passing at that road speed.

That slower chain speed fools the unit into seeing the road speed as that much slower and it therefore allows a higher percentage of phase down power than previously.
.

 

[Polar753]

I'm being thick here but I'd appreciate a little guidance.

Changing the front cog from 9t to 11t will leave the gearing the same but raise the power band it seems to me. Is that correct?

But presumably, since the chainwheel and rear sprocket stay the same, for any given speed and gear the cadence will remain the same?

So if the cadence is 40 at 15mph with 20% power assistance, with the 11t cog the cadence will remain 40 at 15mph but the power assistance will be 40%, all these being illiustrative rather than actual figures, of course.

As far as I can tell, 50Cycles have the 11t cog in stock, by the way.

One 11t cog on the way. Thanks, if it stops snowing hope to get it fitted and try it this week.

 

[lemmy]

Got it.... and thanks!