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Discussion Starter · #1 ·
I have recently picked up a Giant Tran Send with an Alfine internal gear (I know it’s not single speed, so I’m kind of cheating here). The bike came with a tensioner because the frame has a vertical dropout. I managed to change the gear ratio so the chain length is exact, if not near, so a tensioner won’t be needed… There is a little bit of slack but not enough to worry at this point… BUT… as the bike is still very new (only about 200km) and the chain is probably not fully worn-in yet, I’m expecting the chain to build up even more slack. So…

How much slack is acceptable?

Do I need a tensioner to take up the slack as it build-up before a new chain is needed?

The photo shows how it look like without the tensioner.
 

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Proper tension = cranks don't bind and chain doesn't fall off. If you can accomplish that without a tensioner then one isn't needed. I run a similar setup on one of my bikes and just replace the chain when it gets too slack due to wear. Yeah, they do get replaced more frequently this way but it's a small price to pay to keep my bike tensioner-free. Did I mention that I don't like tensioners? ;)
 

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aphleung said:
I have recently picked up a Giant Tran Send with an Alfine internal gear (I know it's not single speed, so I'm kind of cheating here). The bike came with a tensioner because the frame has a vertical dropout. I managed to change the gear ratio so the chain length is exact, if not near, so a tensioner won't be needed… There is a little bit of slack but not enough to worry at this point… BUT… as the bike is still very new (only about 200km) and the chain is probably not fully worn-in yet, I'm expecting the chain to build up even more slack. So…

How much slack is acceptable?

Do I need a tensioner to take up the slack as it build-up before a new chain is needed?

The photo shows how it look like without the tensioner.
Allowed slack depends on the teeth of the chainring/cog. If you can push the chain so that it derails at either end then it's too slack.
 

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pacman said:
Allowed slack depends on the teeth of the chainring/cog. If you can push the chain so that it derails at either end then it's too slack.
define push?

i have the same question as the op, with similar tension as in the pic.

i can push my chain off the chain ring in the front enough to get the side of the chain on the top of the tooth...and spin the crank and get it to derail itself. but its never derailed on the trail by itself. and i can't simply pick the chain up and take it off the chain ring...i need to pedal it all the way around.
 

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whoa there, that sounds like a lot of slack!

nomit said:
i can push my chain off the chain ring in the front enough to spin the crank and get it to derail itself.
It depends if you are using single speed specific chainring and cog. If you are using a chainring built with shift ramps and ramped teeth, you need a LOT tighter tension than you can get away with the tall teeth of a single speed specific chainring.

Spin cranks to find the tightest position, as most chainwheels / cog combos are not perfectly round. At this point, deflect the chain 1/2" or 13mm. As tight as possible without binding, I come to find, is a quarter inch up and a quarter inch down equals a half inch of total deflection in the chain's center between chainring and cog.

Use single speed specific teeth, and you'll do great with a magic tooth count / chain stay length set-up. No tensioners are magical. Vertical drops for convenience and disc brakes. You just can't ever change your gearing - exception is geared hub as in the Original Poster's example above.
 

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nomit said:
define push?

i have the same question as the op, with similar tension as in the pic.

i can push my chain off the chain ring in the front enough to get the side of the chain on the top of the tooth...and spin the crank and get it to derail itself. but its never derailed on the trail by itself. and i can't simply pick the chain up and take it off the chain ring...i need to pedal it all the way around.
What you should worry about is lateral flex in the chain. That's where derailments start. Vertical slack allows more space for the lateral flex to take effect. As a chain wears the lateral flex increases so an old chain and a new chain with the same slack will behave differently. Taller teeth resist derailment, how much (vertical) slack you have is secondary.

So the key is -- can you push the chain and start a derailment?

I'd make the push as a hard effort with your hands or equivalent to some object striking the chain - in all cases your pedaling will do the final work of derailing. The derailment will happen at the worst time - when you're standing and really bearing down on the cranks. Of course there's the factor that you are also twisting the frame so that the cog and chainring are not aligned.
 

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I can't tell what tires your running but if your on the street(commute/recreation) it should be fine, if you off road or hard urban riding than i would try to run a tensioner or use a half link if it will help
 

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Discussion Starter · #11 ·
Thanks for all the replies!

nomit said:
i can push my chain off the chain ring in the front enough to get the side of the chain on the top of the tooth...and spin the crank and get it to derail itself.
I can do the same, but i really have to try hard.

danthesoundman said:
It depends if you are using single speed specific chainring and cog... At this point, deflect the chain 1/2" or 13mm. As tight as possible without binding, I come to find, is a quarter inch up and a quarter inch down equals a half inch of total deflection in the chain's center between chainring and cog.
I'm using a SS specific chainring, and I can deflect the chain about 1/4" down (pushing really hard) and 1/2" up.

pacman said:
What you should worry about is lateral flex in the chain.
So will replacing the chain with SS specific chain help? If yes, which one will you recommend?

Schmucker said:
How's the Alfine working? I want one for my touring bike.
The Alfine is great, super quiet, and I can change gear when I stop, a great bonus for commuting. Just have to get use to stop peddeling when changing gear.

scooter916 said:
I can't tell what tires your running but if your on the street(commute/recreation) it should be fine, if you off road or hard urban riding than i would try to run a tensioner or use a half link if it will help
It's street tires... I may add a smaller tensioner in the future if needed, something like the Sette Tensioner. Anyone with has experience with Sette product? I also read about using a zip-tie to secure the tensioner. Is that really needed?
 

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Discussion Starter · #12 ·
Just came back from a 50km ride through all different kind of surface imaginable (street, bike path, forest/dry mud, thin rock/sand, and even some old 17th century rock paved road). Chain didn’t come off, which is good… but it did however bounces around more without the tensioner. It was a bit noisier when going through rougher terrain. I guess this is a tradeoff of having no tensioner.
 
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