Wet to BPW last Friday and had a superb time. However, in the afternoon I found my bike started to drop the chain more and more. I’ve not really had this before with it (just on the odd occasion) and so annoying.

Bike is a Boardman Pro FS with a full Sram X9 2 x 10 group on it – the rear mech has a clutch. That mech has taken a pounding though in the last year. When I last measured the chain for stretch (a couple of months back) it was still ok. I haven’t checked it this week as had a shoulder operation so can’t get the bike up on a stand right now.

Why might the chain suddenly have started falling off?

Chain knackered?
Clutch in derailleur failed?
Could it be just because I’m suddenly faster over rocky terrain?

I have recently been riding Cwmcarn plus some natural stuff so I do find rocky trails normally that haven’t previously been an issue. At BPW we were riding all the blues and all the reds but no blacks.

All the gears still shift well so unless the top limit screw on the front mech has suddenly gone out of adjustment I’m a bit stumped.

Thoughts?

Chain knackered?
Clutch in derailleur failed?
Could it be just because I’m suddenly faster over rocky terrain?

Yes.

Measure the chain or if you’ve had it some time no doubt it will need replacing, that could of course mean a new cassette as well so you ‘could’ try some form of chain retention instead (just in case you are riding faster/rougher stuff).

Does it fall off the big chainring or the smaller one ?

Does it make any difference which gear you’re in at the back ?

Does it fall off the top of the chainrings, or from the bottom ?

In my [thankfully] limited experience of dealing with this, I think it’s been an issue with the chainring being worn, and not a worn chain, but it could be the latter.

Can’t you simply try pulling on the rear derailleur with clutch disabled/enabled to determine whether it’s working or not ?

Hi there – it was falling off the big chairing – to the outside. Hever had it before and if I change the stop screw on the derailleur it won’t make it up into the big chainring.

I rarely use the big chainring in fairness – so I don’t think it can be torn out. No bent teeth either.

If I change the chain I should irkvably change the cassette too – but if I do that did the problem is still there then I’d be miffed.

Tempted to save up and go 1 x 11. I can’t ride my bike for at least 12 weeks (and then on the road / easy flat trails) as just had shoulder surgery to repair a torn labrum.

Only thing is that’s money that could go to replacing my 150mm revelations with 150mm pikes. Went to bpw the other day and loving the no riding up / smashing it down all day.

Do you need the bike on a stand to use a chain checker?

Best to rule that out before you do anything else.

Fair point – I’ll get the free mbuk chain checker out on the weekend and see what occurs.

Think it has two measurements 0.75 and 1.0 perhap’s? If the former then change just the chain – if the latter then maybe too late and need to change cassette and chain?

Adjust the clutch go to http://m.pinkbike.com/news/ask-pinkbike-april-7-2015.html for instructions
Mine did this recently, adjusted and no probs now!

Maybe the derallieur has taken a knock and the mech hanger is slightly bent.
Same symptoms as mine had a while ago. Could just about make out that the mech was skew. LBS got their hanger straightener tool (Park tools) on it and it is fine now (5min job).

Hi there – it was falling off the big chairing – to the outside

Can happen if the front mechs not mounted low enough, I always try to get it as low as possible so as it just clears outer ring.

Think it has two measurements 0.75 and 1.0 perhap’s? If the former then change just the chain – if the latter then maybe too late and need to change cassette and chain?

Only one way to find out, but yeah change at .75 and in theory you should get three chains to a cassette.

dirtydog – Member 
Only one way to find out, but yeah change at .75 and in theory you should get three chains to a cassette.

While it can be a fact that you may get three chains to a cassette. Try one chain to death and likely the cassette will last just as long, if not longer. Certainly my experience having tried both methods.

Cheers for all the comments guys. I’ll check chain stretch this weekend and the height of the front derailleur. Didn’t know you could adjust clutch mechs. I know you can’t switch the sram one on and off like shimano ones though.

The bike has a new mech hanger on it. So if anything is bent it would be the derailleur. Although it hasn’t had a knock for ages and the chain thing only just started happening.

New mech hangers aren’t neccasarily straight.

They should always be checked once they are installed.
Should always try and check them on new frames/bikes as well…….

I mean it looked straight to the eye. Think it’s a cnc’d aluminium one rather than a cast one. The bike is a boardman pro fs and the original one was made of cheese. I set the rear derailleur up after changing the hanger as I out a new shifter in St the same time.

I mean it looked straight to the eye.

You’d be amazed at how bent a hanger that looks straight actually is……

And it’s not just the hanger, it’s the shape and flatness of the frame where it mounts that has an effect too.

To how would I check it’s exactly straight?

When I had this 2 weeks ago, it was loose chainring bolts. Also look at your jockey wheels.

I was going to suggest one of these
http://int.oneupcomponents.com/collections/all-products/products/top-guide
Then i read you had a front mech 🙄
So i suggest one of these
http://www.ebay.co.uk/itm/RSP-Chain-Guide-MTB-Bike-Chainguide-Director-Tensioner-Universal-Bike-Drop-/331520481153?hash=item4d30291781:g:YmUAAOSwstxVAFN3
😀

Freehub?

Mine did it after I serviced the hub. Had to thin the grease down…

It pushed slack onto the front sprocket. It was worse lower down the cassette

To how would I check it’s exactly straight?

With a straight edge, dear Liza… 🙂

Sorry… couldn’t resist. A 6″ steel rule is ideal, I keep one in my toolkit on one of those little shelf things so it sits flat and stays straight. Take the wheel off and if you need the space, the mech too and hold the thin edge of the steel rule against it – you hope to see metal square against metal when you sight at this. If you can see the frame or hanger bowing away from the straight edge, and you’re sure the straight edge is straight, it’s a bent hanger or frame.

To how would I check it’s exactly straight?

http://www.pinkbike.com/news/park-tool-derailleur-hanger-alignment-tech-talks-video.html

I’d be looking at chainring wear initially. More worn the more likely it can drop. Front mech issues would mainly be if it’s misaligned and is rubbing the chain thus pushing it off. Many will fiddle with the front mech to keep a chain on or use chain retention devices but often it’s just worn chainrings.

Other than that, rough downhills tend to bounce the chain a lot and can have it bounce off easily. Chain devices and clutch mechs are solutions for this, although I found a clutch set up still needs a chain device at downhilly type of venues. As said though the clutch may need adjustment or service if it’s too slack.

I finally gave up with 2x though when at Stiniog and chain just kept coming off on each run. Chainrings not that old, fresh cassette and chain. Tried a chain device after that but I’ve not had much luck with 2x devices (one got chain jam and just ripped apart, and then I had issues with the device tending to drag the chain off the big ring).

Solution – 1x with a narrow wide chainring (plus clutch)

Chain drop gone and no need for a chain device either in my experience. Much simpler, less cluttered controls, no front mech, easier to clean.

However still watch out for chainring wear. It will start dropping once it’s fairly worn, even a narrow wide chainring.

So it’s chain wear and clutch in mech main things to check. I can’t believe my big chainring is worn out – I’ve barely used it. The small one is much more likely to get worn. Although the whole groupset is only a little over a year old and on its first chain still. Kept it immaculately clean – although it has had some muddy / wet rides.