Have been riding and enjoying my Alfine hubbed bike for a few months now, but under very hard cranking it has a tendency to throw the chain off the sprocket.

Now I've never owned a singlespeed before, but I know how to set the chain up on one etc. The bike is a On One Inbred 29er (slot dropouts) fitted with a Shimano Alfine hub with a 22T Nexus Sprocket, a 34T chainring and a SRAM PC1 chain. It's not affected me too badly, only having thrown the chain twice with me on, but I lent the bike to a mate today who normally rides singlespeed, and he threw the chain maybe 6 times in 2 hours! Including one knee to stem interface…

Right, The chainline is not perfect, but it's pretty good, the chain is set up pretty tight (but without being too tight, certainly less slack than most Singlespeed bikes I see), the chain/sprocket/chainring were all brand new at the same time which was approximately 6 rides ago, and everything is setup as well as it can be…

So what the hell is the problem??? I'm totally confused! My mate did say that SRAM PC1 chains were crap (which is a shame as I'd had them recommended to me on here by singlespeeders!) but I can't see that that's it? His own singlespeed has a worse chainline, and a much slacker chain, and it never throws its chain so why does my bike?

It's cuz you is a gayer, init! 😉

Crap chain line, singlespeed chain, flexi back end, worn rear/front cog, any combination of these.

Ramped chainring? I always use an unramped one that has taller teeth that do not encourage the chain to go off to the side.

Is there a distorted link in the chain?

Take the plastic guide off and flip the sprocket over?

Crap chain line, singlespeed chain, flexi back end, worn rear/front cog, any combination of these.

Exactly as I thought, only the chainline is quite good and the cog and chainring were brand new not long ago. And whilst I suspect my inbred isn't the stiffest frame in the world, I also suspect it's not the flexiest as it's certainly more overbuilt than underbuilt.

Would it be wise to try an 8spd chain instead of the 1/8th inch SRAM PC1 on it now, or will this make F all difference?

It's cuz you is a gayer, init!

LOL, something like that mate yeah… Anyways, forgot to tell you, I finish early (midday) every Friday, so if you're up for friday afternoon rides at all ever, just let me know, I'll bring a bike with me to work…

Ramped chainring? I always use an unramped one that has taller teeth that do not encourage the chain to go off to the side.

Is there a distorted link in the chain?

Nope, it's a proper unramped single ring only chainring (Shimano Saint 34T). Besides, it keeps coming off the rear cog, not the chainring anyway.

No distorted links in the chain either!

Take the plastic guide off and flip the sprocket over?

Got a 22T Nexus on it mate, doesn't have the plastic guard on the cog. And the sprocket is flipped to give me a better chainline anyway…

Besides, it keeps coming off the rear cog, not the chainring anyway.

bad chainline then 😉

Eight speed chains do seem to be less prone to throwing as they sit tighter on the chainring/cog.

If you're running 3/32 ring & sprocket, yes, try a 3/32 chain, not one 33% too wide.

too wide chain and bad chainline?

Bent arm on spider? I had one causing about 1mm (IIRC) of movement in the ring that was enough to cause similar issues.

Bent arm on spider?

Nope, cranks are all good, no bent spider

bad chainline then

I took the time and effort to get it as good as it could be. It's not 100% dead on, but it's pretty close. I'd have to machine down some custom BB spacers for my HT2 BB to get it any better! So that means it's within a couple of mm of ideal to be fair.

Cheers Stu, will try an 8spd chain then. Any suggestions or will any old 8spd chain suffice?

Any 8 or 9 speed chain will do.

Cheers Stu, will try an 8spd chain then.

I prefer the unobtainium 8 speed Ti chain myself. 😉

Eight speed chains do seem to be less prone to throwing as they sit tighter on the chainring/cog.

Not being funny but my dropped chains stopped the moment I went from 8s to 1/8 chain (and I don't see how one chain can "sit tighter" when they have the same link-length)

OP – v difficult to diagnose at arms length as you seem to be doing everything right. Pics?

Not being funny

That's the only thing that you've ever said that i believe. 😉

Not being funny but my dropped chains stopped the moment I went from 8s to 1/8 chain (and I don't see how one chain can "sit tighter" when they have the same link-length)

OP – v difficult to diagnose at arms length as you seem to be doing everything right. Pics?

The chainring and cog are designed to be able to be used with a 3/32" chain, hence are thinner than if they were designed to be used with a 1/8" chain only. I am using a 1/8" SRAM PC1 as recommnended to me for strength and durability (though I'm SERIOUSLY doubting that recommendation as it's grown loads in only 6 rides as it is!), though I've never broken an 8spd chain in the past, though to be fair I've been on 9spd for a decade now and I have broken a couple of 9spd chains in that period.

stu – heh.

OP – 1/8 chains are way less flexible. As for "strength" it's all a bit random as chains break not due to lack of strength but a link breaking – possibly through imperfect join etc.

OP – 1/8 chains are way less flexible

Nail/head. If the chainline's out a bit this can be enought to derail the chain.

How about a 3/32 Izumi track chain? It's got very deep side plates and it's a proper bush chain so should stretch less and flex less. Shiny too!

And maybe try some chainring spacers? That should get the chainline properly sorted out.

I may be wrong on this but I think the spacers that come behind 10 speed road cassettes are the same diameter as BB spacers. If you could find enough of these (about 3 I guess) then you could fine tune chainline with the BB offset.

I had this problem on the hub geared ride to work bike, which has a very poor chainline, and cured it by running the chain a bit slacker than I felt ideal. I suppose it allows any misalignment to be taken up in the chain without actually pulling it to the side ie a bit more flexibility.

PC1 chains are fine I have them on a single speed and a couple of road fixies

PC1 chains are fine I have them on a single speed and a couple of road fixies

Not what all the singlespeeders I know that are hard on kit say! They won't touch them with a bargepole so I found out… Seems the one I was using has stretched A LOT for only half a dozen rides old too!

Slapped a cheap KMC 8 speed of some descript on there this morning, went riding, tried to throw the chain off and it seems pretty well stuck on! Cheers for the tip guys, hopefully the 8speed chain has sorted out my woes…