This is mostly my winter bike but has been out again (on slightly harder ground than February’s) since the rain started a bit ago

frame has slotty dropouts & chain is tight to very tight (tightened to “very” after 1st loss)

chainring is a FSA “dh” one that supposedly is really a SS one

granted it’s a cassette hub but the sprocket is a poshish on-one one with the wider base and chainline is spaced bang on as far as I can see

8sp chain (could it be too wide for drivetrain – should I go to 9sp ? I’m just using up a spare older chain)

so, WTF ? 🙁 – 3 times now. not massive usage, chain still within limits using a checker

Haven’t yet fallen off or severed any bollocks, but it’s coming I’m sure

Had similar problems with an SRAM PC-1 chain. Ditched it, bought a KMC chain, and never looked back. The KMC stays on even when its slack, only time I’ve dropped it is when a branch got wedged between the sprocket and chain.

It sounds a bit trite, but if you’re running an SRAM chain, might be worth swapping for KMC.

Your chain tension should not be tight that will screw your bearings.

Did you check your chain line with no chain installed? Having a wider chain than needed is no issue, in fact I have a cheap £5 1/8th ” chain on my bike at the moment.

chainring is not mounted true on the spider allowing loose spots ?

Your chain should be able to move up and down by 1/2″ in the middle. “normal” chains are crap for ss – go kmc.

when I say “tight”, chain was “correct” – then went to tighter than ideal when it 1st jumped to see if that stopped it (didn’t, so will slacken off again for nect time)

think I will have to try a different chain – my mate has a SS chain on a vertical dropout frame now with about an inch of play and using a normal chainring and still stays on better than mine.

(Edit – trailrat, I don’t see what you mean; bolts are tight and no side to side wobble. Something else ?)

Final thought: I suppose my ossum power output might be bending the frame so much that the chainline goes out 😉

(edit again – thanks for the suggestions)

Hmm not sure, I’ve been running a normal ramped chain ring on a Shimano 8 speed chain and not had any slip but I have flexed the frame sufficiently to get some tyre rub on steep climbs..

you can have the ring mounted on the spider but due to oversized holes the ring can be eccentrc on the BB axels rotation , resultng n loose spots and tight spots in the chain.

look on sheldon brown for an better explanation

No problems here with PC1 chains, other than they seem to break a bit too frequently. Only had it jump off the front once in over 3 years when I let it go a bit too slack.

My guess (and I’m very much guessing) is that chainring isn’t as ‘singlespeed’ as you need it to be. Maybe as a DH ring it’s designed to run with a chain guide and needs taller teeth?

Not boasting here but I have never had a chain come off in several years of single speeding. That includes some less-than-ideal setups in the early days using ramped chainrings and knackered old chains.

There must be something fundamentally wrong with your setup but apart from the fact that you don’t mention that you have checked the chainline, it all seems on the face of it okay to me.

Even using a ramped chainring I can’t see how the chain would come off unless it was a) very slack or b) out of line.

The only other thing that hasn’t been mentioned is the possibility of the wheel pulling over to the drive side under load. You say you are using slot dropouts. Are you using QR hubs and do you have a chaintug fitted on the drive side? What is the frame that you are using?

chain line, BB on the way out or as above no chain tug?

I run a rotor eliptical ring on a single speed with no problems or chain drop so a slight tight-slack is not a problem unless the chain line is out

oooh more help – ta !

chainline checked visually (“bang on” to my eye as suggested in OP) – is there another way to check ?

No obvious tight/slack spots on the chainring as it turns

It’s one of the chainrings that bikemonger charlie sells (FSA DH) “These are very nice rings, on par with the salsa rings. Its just a case of FSA not knowing what they have here, you see they list it as a 1×9 style downhill ring, which is exactly the same a as a single speed ring”

Driveside chaintug in place, admittedly only QR axle but axle isn’t displaced when the chain comes off, so unless it slides back again that’s out

gonna change the chain & try again, I think (it’s the cheapest & easiest and maybe most likely suspect)

chainline checked visually (“bang on” to my eye as suggested in OP) – is there another way to check ?

geeky, but I use a long spirit level from the chainring back to the rear cog. You be amazed how many times it’s looked spot on, only to be about 5mm out

i run pc1 and didnt have a prob at Mayhem so theyre not all that bad a chain. Like said previously, maybe the front ring giving u gipp…. If its a 1/8″ chain, u gotta have a 1/8″ front ring SS specific to help run smoothly. Solo Velo do em for £25. Bosh
Only my opinion, learnt the hard way!!

Hope this helps,

G

If its a 1/8″ chain, u gotta have a 1/8″ front ring

I’d disagree – been running an 1/8″ chain for years on a 3/32 Middleburn Uno ring, without any problems.

As I said before I have used all sorts of combinations of ramped chainrings, cogs from split cassettes, worn old chains of no name, 8-speed, 9-speed and 1/8″ chains and haven’t really experienced any problems apart from a bit of drive train noise sometimes.

I have used an FSA chainring quite successfully in the past as well.

My preferred chains now are Wippermann Connex 8-speed because they have a brilliant design quick-link which is so easy to get apart.

My only other suggestion is to try another chainring, even a shonky ramped one from a geared set of cranks and see how you get on and maybe another chain.

If its a 1/8″ chain, u gotta have a 1/8″ front ring

Rubbish, I’ve done over 20,000 mile on road with a 1/8 chain + ramped and pined 3/32 ring and a minimum of 2-3000 miles off road with a similar setup.

Use a chain that is not purpose designed to slide easily off the cogs, ie don’t use a derailleur chain if you can help it.

BMX chains are the go.

chainline checked visually (“bang on” to my eye as suggested in OP) – is there another way to check ?

Measure the distance from the centre of the down tube to the centre of the chainring. Subtract that from 67.5mm (half of 135mm). Your rear cog should be that distance from the inside of the drop out.

Is the wheel straight in the drop outs?

Now this may just be me ,(so feel free to point and laugh)but I am the only person in my gang that tensions their chain this way not the usual way

The chain has never come off,is this just luck ?

Okay, measured chainline. 2.5mm out – is that enough to drop the chain ?

fasthaggis – your way wraps more chain round the cog, which must be a good thing

I’d go with a KMC. In fact I always do.

Cheap enough, if not just to rule it out as a fix.

One other thought that came to mind – as per above – have you got a chain tug fitted? I think they help with general bodgery and singlespeed voodoo.

fasthaggis – I used to run mine that way round too. I had one of the old Surly tensioners that came with a ‘push-up’ and a ‘pull-down’ spring. I used to drop the chain though, I couldn’t get the tension high enough to deal with the excess chain my frame ended up with.