Hi ,

Can anyone tell me what kind of chain tension should I be looking for on a hub geared e bike ? Bike is a kahlkoff with nexus 8 speed gears

Is it similar say to a fixie or singlespeed road bike where I want an inch or so of up down play each way when setting chain tension ?

The chain tension can only be adjusted by moving the wheel back or forwards in the semi horizontal dropouts .

Thanks for any hep ,

J

The right tension is no tension. Chain drive systems require some slack in the return loop. The ideal adjustment allows minimal slack at all times.

Because there's some eccentricity in the sprockets the amount of slack will vary, and you need to allow for that. A general rule of thumb is 1/4" vertical free play at the center of the lower loop. Then rotate through a few pedal revolutions to confirm that there are no tight spots.

"Chain tension" is a poor term for a systenm that wants NO tension. But we all use it, like refering to cable tension changes when adjusting SIS coordination (when it's cable length that is actually changing).


The hub's internals don't want a chain that has any tightness which would cause the cog/driver to rock or be pulled off line (from what the internal to hub stresses create). In fact a slight slop in the hub's bearing adjustment is often also needed for the internals to be able to slide, engage, freewheel relitive to each other. Coaster brake hubs and single speeds are also included in this. It is a common practice to have a tiny bit of side play when pushing/pulling the rear rim with IGHs.


So this need for a tiny bit of slop in the system includes the chain. That many rings and cogs are not truely round means that the "chain tension" varies as the crank, rear cogs and chain are rotated and go through each of their own cycles of tightening/loosening of the chain. We set the chain so that at it's tightest point it is still very slightly loose. The loosest spot then is what it is.


It's easy to check this out by pulling back the rear wheel as far as you can and tightening it there. Then slowly turn the cranks and watch the rear cog. When the chain passes through it's tightest point the cog can flutter, rock, become sticky in it's rotation movement (as the bearings that the driver rides on are over loaded from the tight chain). Then loosen and move the rear wheel a bit forward and repeat the slow cranking. The rear cog will seem far more free in it's movements.


Which do you want? A system that won't drop a chain but wears out rear fast and works poorly all the time or a system that rides (and shifts) smoothly and lasts a long time but likes a rider that isn't a square pedaling masher. There's a reason that 50 year old IGHs are still running when same age coaster brake bikes rear hubs are ground up/pitted on their ball tracks. Proper initial set up and follow up maintenance. (Remembering that most coaster brake bikes are big box sold and poorly assembled). Andy.

I, of course, agree with Andy, with one exception:

I find almost every hub can be adjusted to have no play, but on lower quality/more complicated hubs, the difference between free-spinning and too loose/tight is very pronounced.

I find even the much maligned KT coaster can be adjusted to work with no play, after one has wrapped their head around a few of them. I find the easiest way to adjust them (and IGHs, too) is to clamp them in the dropouts as normal, loosen the axle bolt on the adjusting side, and slide two cone wrenches (though I find a typical 17mm combination wrench of any quality will fit, along with the proper come wrench) in past the dropouts, allowing a very sensitive adjustment.

Actual longevity is another story, but as far as function when new? Very attainable. The KT in particular got a bad rap, I suspect because by the time most people saw one for service, it was beyond saving. IGHs (of the beach cruiser variety, popular around here) will suffer a similar fate as they begin aging; I hear so many people tout them as "maintenance free", when really, they should at least be inspected every couple thousand miles...gone are the days where you could just drop a few mls of oil through the port on the hub shell.

While Andy mentioned hub related issues, the fact remains that chain drive requires slack regardless of the hub or bearings.

Consider, the hub is being driven by the tension in the upper loop. The lower loop simply returns "used" chain to the rear sprocket so the process can continue. So no lower loop tension is needed, nor is it wanted since all that non-driving tension does is pull the rear hub forward, increasing the load on the axle and bearings.

The drawing below shows the industrial guideline for proper tension.

The 2% guideline translates to about 1/4" on a typical bike.

I have always made the chain as loose as possible, but tight enough that I can not push the chain off the chain ring (using an open ended wrench to push on the chain).