Single-Speed Chain Tension

[sizbut]

Okay, its driving me nuts. Every article on this is simple vague, far too many "not too tight" or "just a little slack" statements with no actual measurable definition.

So, with the bike stationary, the upper chain section dips. Apply some pressure to the pedals and that chain section lifts to become a taut line. So what amount of dip/lift equates to a little slack but not too tight?

Any other way of quantatively measuring chain slack and acceptable slack also welcomed.

[PaulF]

I usually try for about 1/2" movement vertically. But that's gone out of the window now I'm running an oval chainring

[Basil]

Post a shot of your bike on the "Member's Bikes" thread.  You'll be informed in minutes. 

[nightrider]

If its a freewheel chain tension is not as critical as fixed wheel.I think saggy chains look crap though.

[LittleWheelsandBig]

Too slack = chain falls off. Too tight = excessive drag and wear. If you can push the chain off (with a spanner) while the pedals are turning, the chain is too loose.

[Biggsy]

Start by having it on the tight side, then ease off until there's no excessive drag when turning the cranks backwards.

It's too tricky to quantify it with measurements.  Go by feel.  You'll get to know what's right and wrong.

[zigzag]

tighten axle nuts while gently pushing the wheel back. the chain should sag only tiny bit between the chainring and cog, like on this bike for example:

[Henry]

tighten axle nuts while gently pushing the wheel back. the chain should sag only tiny bit between the chainring and cog, like on this bike for example:

Pffff, what would the owner of an old granny bike like that know 

[rogerzilla]

No visible droop is good, but there should be no tight spots when turning the pedals forwards or backwards (with some gear combinations, you may have to turn them many times to find the point where chainring and sprocket maximum diameters happen to coincide, although in practice most out-of-roundness is from the chainring).

On cheap bikes it is usually unavoidable to have a slack chain at one point in the rotation to avoid a tight spot elsewhere.

[Crumbling Nick]

If its a freewheel chain tension is not as critical as fixed wheel.<snip>

That's a crucial point. Chains don't normally derail at low cadence & if they do the consequences are rarely serious. If you regularly pedal high cadences downhill (unusual, but I might do it), then the consequence of derailing is far less likely to be life-threatening than with a fixed gear, because the freewheel disconnects the chain from the back wheel, unless the chain drops between the sprocket & spokes. In that event the outcome is less predictable, but is very unlikely to be worse than with a fixed cog.

Chain tension needs to be maintained regularly & systematically with a fixed gear. It's frequent enough that it's worth optimising the tightening procedure. This maximises the time between re-tensionings. It's not normally necessary to that anal about it if you have a freewheel. Overtightening will shorten b/b &/or hub bearing life, but a bit too much slack is less critical.

I am unconvinced that there is a universal test for "too slack”. The rule of thumb seem to ignore the differences between fixed, single-speed & hub gear. Also, I can push the chain off my (fixed) chairing with my fingers when the chain has just been tightened, even with a new chain. That's presumably a consequence of an 8-spd bushingless chain, despite a 3/32" chainring which is old enough to have full-width teeth. Doubtless a 1/8" bushed chain would behave completely differently.