16 tooth Sprocket on Nexus hub

[oriteroom]

Hi all,

Just got Mrs 'O' a new Kalkhoff Tasman, which comes fitted with a 21 tooth sprocket and 38 tooth chain ring which gives her low gears she'll probably not use, and it would be better to have some higher gears to allow input at speeds over about 18mph e.g. When she's downhill with a following wind . The gearing is lower than on her 2008 ProConnect and I plan to change the rear sprocket. I've put a 19 tooth one, years ago on my original ProConnect and basically got an 'extra' higher gear. Anyone have experience of putting a 16 tooth sprocket on a 8 gear nexus hub and what change she might experience (e.g. like what was gear 6 becomes gear 4?. Are there any downsides to a small sprocket re gear wear etc. ?

Thanks

 

[Artstu]

Have a play on here http://sheldonbrown.com/gears/

I can pedal to 39 mph on my bike. I've forgotten the sprocket sizes I have.

 

[JohnCade]

I’ve got a Kalkhoff with the same gearing as you, and I was thinking of and still may change to an 18 rear sprocket. That effectively pushes all the gears up one. So top becomes 93” and 7 becomes 82” which is a little higher than the existing top. With that sprocket all the gears just more or less go up one. So bottom becomes 30” which is close to the standard gearing 2 of 32”.

The standard gearing 1 is 26” and I’ve never used it. I live in a hilly area too but I doubt I would ever use it. I don’t go all that fast in the lanes I mostly ride in though and can keep a high cadence when I need to so I haven’t bothered to change the sprocket as yet.

Just to add with the 18 sprocket the cadence at 25 mph is 90 rpm and 70 rpm at 20 mph. Standard gearing is 105 rpm at 25 mph and 84 rpm at 20 mph.

 

[flecc]

The similar Pro Connect with the almost equally restricted-speed Panasonic unit had a 21 tooth rear sprocket. Changing it to a 16 tooth increased the assist speed to just over 20 mph.

Since the Tasman with the Impulse unit has a slightly less restricted top speed, you should get 22 to 23 mph with the 16 tooth sprocket, though at that, wind resistance might knock off 1 or 2 mph.
.

 

[JohnCade]

The similar Pro Connect with the almost equally restricted-speed Panasonic unit had a 21 tooth rear sprocket. Changing it to a 16 tooth increased the assist speed to just over 20 mph.

Since the Tasman with the Impulse unit has a slightly less restricted top speed, you should get 22 to 23 mph with the 16 tooth sprocket, though at that, wind resistance might knock off 1 or 2 mph.
.

I’m not sure the Impulse will do that if you mean increasing the assist speed. I was under the impression that unlike the Panasonic models the software prevents that changing with different sprockets. Although putting the sensor magnet on the crank and moving the sensor close to it has been said to possibly work and dongles are available I gather....

 

[flecc]

Thanks John, perfectly true, I was forgetting about the necessity of moving the speed sensor on these. There's some illustrated information on doing this on my Panasonic support website which could be adapted to the Impulse unit bikes, this link refers.