bmorey

What is the proper chain tension in a bike with internal hub gears? When I bought my new bike (last month) with Shimano Nexus gears I thought the chain was quite tight -- very little droop between the front and rear cogs. Now there's 3/4" drop between the cogs and I think it needs tightening.

I researched this and couldn't get a consistent answer. Sheldon Brown recommends a tight chain on a fixie but that might not apply to hub gears. Another site recommended 1/2" drop between the cogs. I've got the Shimano technical service instructions in front of me and they're silent on chain tension.

Advice gratefully received.

operator

Sheldon brown does not recommend a tight chain. He recommends a chain that is PROPERLY tensioned. Which means not tight enough so that it binds/laser tight in one spot but not so loose that the chain is dropped on a bump.

Variations in cog/chainring/cranksets all produced different results. Some combos have huge variation as the chain goes around, some not as much. This will affect how easy it is to get the proper chain tension.

Chains on ss/fg bikes should ALWAYS have some play in them. Run them laser tight and watch as your drivetrain grinds and self destruct in no time. Having said that you basically have two options of doing it

1) Run the chain tight then progressively move the axle forward until there are no spots that bind
2) Run the chain loose and progressively move the axle backwards until it binds, then move it a tad forward again

Park says 1/2" up/down which is fairly acceptable. You should not be able to push the chain off the cog/chainring by hand if the tension is correct. This will always give you the lower limit on chain tension.

bmorey

Thanks a bunch for the thoughtful advice- it's appreciated. I'm reassured.

BCRider

On my own two single speed bikes I have always just pulled back moderately hard on the wheel with a hand on each axle nut. THen I finger tighten the nuts while pulling. This produces the correct sort of non tension but not loose chain that works nicely. If your bike has screw tensioners then at that point just bring the screws up to contact without adding any tension. The real role of the tensioners is as an axle positioning device and they should not be used to jam tension into the system.

patrick.decker@

I've got a few fixed bikes, and I find that with ~1/2 inch of play, and even some less, will allow you to push the chain off the wheel? Even with a 1/8 chain. Furthermore, I notice any less then 1/2 inch play the system has more friction. So... I still don't know exactly how tight it ought to be?

dabac

(Apart from fixies, which I don't really know about) chain tension has surprisingly little to do with keeping the chain from slipping when pedalling, so the main reason for controlling the slack is to avoid accidental derailing due to bumps and jars.
OTOH you don't start to see excess friction until the chain goes really tight, so there's little point in running it slack deliberately either. A half-inch sag or thereabouts is the happy compromise.

ogbigbird

yeah, as a rider of primarily single or 3 speed bikes, you want about 1/2" play of the chain. not to tight as to cause the drivetrain to bind, but not too loose as the chain has noticable sag and wants to come off the cog/chainring. +1 with everyone else.

G piny parnas

nobody is putting any attention to the "internal geared hub" issue here---- Is he not
asking what chain tension to maintain to maintain his "delicate" geared hub? I would think the maker of the Hub would have this answer...

tellyho

I think that fixed tension and SS tension are also not synonymous. I like a lot less sag with my fixed cog; am willing to tolerate more with the SS. In neither case do you want a whole lot. I ultimately agree with G piny that the OP should consult with the manual. On my SA 3 speed, too much tension binds the whole thing up.

bmorey

Going back to my original post (#1) a day later the chain came off when I went over a speed bump. It dislodged the rubber sealing boot on the hub. I managed to get it back on (no tools on hand). I now follow the consensus here: about 1/2" drop.

G piny parnas: Surprisingly Shimano does not mention this in the instructions. They were the first place I looked.