Kalkhoff what cog?

[lemmy]

I have a Kalkhoff Tasman which has the 8 speed Shimano hub. I'm planning to fit a rapid fire change instead of the twist, which tends to be a bit awkward to use under the constant gear changing needed in London.

I thought I might try a gearing change at the same time. I find the gearing a little too low but I don't want to lose powered range.

For the Agattu 7 speed, many people recommend a 19 tooth rear cog. Would a 20 tooth perform a similar function on the 8 speed?

I'm using the bike in west London and environs, Epsom Downs and so on, so I don't want to lose too much hill climbing ability. Essentially, when the power cuts out at 15mph, by 18mph the old lallies are spinning too fast for comfort.

Any experiences anyone - specific to gearing on the 8 speed, of course?

 

[flecc]

The 8 speed needs to be lifted more really, since it's greater gear range is all added lower on the Panasonic equipped bikes. A 20 tooth will raise your motor assist limits by 1.5 mph and the change in the bottom gear climb ability will barely be noticeable.

A 19 tooth will raise the assist limits by 2.4 mph which I think is more useful and I can't imagine not being able then to climb a hill in those areas in bottom gear on the 8 speed hub.
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[Barry Heaven]

I fitted a 19 tooth sprocket on my 8 speed Alfine hub Pro Connect and it feels just right now. It did lop about 1/3rd off its range though.

 

[lemmy]

Thanks for that. It's a bit of a headache, I want the higher gearing but not to lose the range - something for nothing, in other words.

 

[Barry Heaven]

So do I, but no free lunch I guess.

 

[flecc]

Thanks for that. It's a bit of a headache, I want the higher gearing but not to lose the range - something for nothing, in other words.

With maximum power at up to a cadence of 40 which corresponds to 9.4 mph in top gear on the standard 8 speed setup, in bottom gear that's just under 5 mph optimum climb speed at a 40 cadence, though you can climb slower still with maximum power at a lower cadence.

Changing to the 20 tooth sprocket lifts that maximum power climb speed at a 40 cadence to 5.4 mph, with a 19 tooth to 5.7 mph.

You can see that the effects at the bottom end are not severe and you should still be able to climb almost anything just the same.
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