Chain Tensioner?

[TomB]

I was thinking about a way to enable the switching of rear hub gear sprockets without changing chain length - to support different terrains etc...

Have been wondering about the possibility of fitting a chain tensioner to the hub gear set up on the kalkhoffs currently around. Assuming that it is not possible to adjust chain tension to accommodate the range of available sprockets within the motor/crank assembly (is it?).

I seems most of the available chain tensioners, e.g. Tension Seeker, are designed to pick up the slack from vertical dropouts after a fixed gear conversion. Because of this they rely on the gear hanger (dérailleur) hole in the drop out. Does any one know if the kalkhoffs have a spare hole in the dropout or of a chain tensioner that does not rely on the gear hanger hole? I found one system that clamps to the chainstay but it doesn't look like it will manage much slack as it seems to mainly be to stop the chain jumping off.

Or generally does this sound like a sensible idea...

 

[frank9755]

I don't quite understand what problem you're trying to solve, but to answer your question in the context of whether it would be a good idea to take a Kalkhoff on a variety of terrains, the answer would be 'no' - as electric bikes are road only; bumpy terrain is liable to damage battery mountings and other sensitive bits.

Frank

 

[TomB]

juat roads

terrain as in 16 teeth for hilly roads, 22 teeth for flat roads. e.g. you could live in east anglia and go on holiday in north wales... very different roads.

 

[TomB]

sorry other way around 16 flat 22 hilly.

 

[flecc]

I think it's much better to adjust the chain when changing sprockets, and one way to do that would be to have different length insert sections using Quicklink connectors.

However, you can use a chain tensioner on one of these bikes, but the tension applied should be limited, since it could otherwise be "fighting" with the tensioner that's already on the Panasonic unit. That one exists to provide stable tension across the motor drive sprocket, insulating it from the chain thrash that occurs on the non-drive side lower chain run. Here's the tensioner with the bike in an upside down position, but it's hasn't enough range to do the job you want, so another would be necessary:

Although Frank is correct that e-bikes in general aren't suited to rough ground use, of all of them, the Panasonic motored bikes are the most suitable for that, since the central motor doesn't suffer direct wheel shock, is extremely robust with a cast alloy crankcase, and is waterproof.

P.S. Just seen your additional post on the hills and flat use. If it's the 8 speed hub the gear range will probably be more than adequate without this measure. It's only geared so low with a 22 tooth rear sprocket to keep the maximum assist to the legal 15.5 mph. Most find the low gears go too low as a result, the first and second not used or very rarely used. Even the 7 speed has more than enough range for most uses. There is a limit to the speed the small motor can assist at anyway, so that restricts the upper end. Although many seem to be considering a 16 tooth, I think that's a bit high a gearing for these bikes, hence my general recommendation of around 18/19 tooth.
.

 

[TomB]

i currently have two cassettes for my road bike - a 12-23 for hilly areas like the lakes or an 11-21 for "normal" terrain. so was wondering if it was possible to do something similar with hub gears.

 

[flecc]

i currently have two cassettes for my road bike - a 12-23 for hilly areas like the lakes or an 11-21 for "normal" terrain. so was wondering if it was possible to do something similar with hub gears.

The SRAM DualDrive does similar, a combination of a three speed hub to give three ranges, and an 8 or 9 speed cassette. It's a very successful system with a huge range, and it is in use on some Panasonic system bikes:

As an alternative, you could get a local engineering company to cut out the centre of a 22 tooth and weld it with a thin spacer onto a 16 tooth. Then with a jockey wheel tensioning the chain, you could flip the chain across manually between the two sprockets. There's a similar arrangement for Brompton folders, turning a three speed hub into a six speed.
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[TomB]

yes, thanks flecc. i've also seen the dual drive used on folders to simplify the chain wheel set up.

i think i'm more in the world of changing-the-gearing than changing-gear; something i do only a few times a year (if at all) - if you see what i mean.

think just altering the chain length each time is probably the better solution.

thanks for all the help, much appreciated.