Why does my chain keep jumping off my little ring.

shdaxner

How do.

I have a Boardman team carbon with sram rival groupset and compact sram s350 chainset, this morning for the 3rd time in a couple of days my chain jumped off the small ring when I was out of the saddle cranking up a pretty steep bit of hill, the steepness caught me by surprise so I was pushing more than I normally would be in too high a gear but the chain jumped off the ring and I nearly fell off into the road....this has never happened to me before on any of my other bikes.

I have had a look a the drivetrain and the rings or cassette are barely worn at all and the chain is also fine? gears are indexed correctly shifting perfectly under normal circumstances.

Any ideas as to why this keeps happening?

DiscoBoy

shdaxner wrote:

How do.

I have a Boardman team carbon with sram rival groupset and compact sram s350 chainset, this morning for the 3rd time in a couple of days my chain jumped off the small ring when I was out of the saddle cranking up a pretty steep bit of hill, the steepness caught me by surprise so I was pushing more than I normally would be in too high a gear but the chain jumped off the ring and I nearly fell off into the road....this has never happened to me before on any of my other bikes.

I have had a look a the drivetrain and the rings or cassette are barely worn at all and the chain is also fine? gears are indexed correctly shifting perfectly under normal circumstances.

Any ideas as to why this keeps happening?

Because your front dérailleur isn't set up correctly. You need to adjust the limit screw.

I also recommend to everyone that they use a chain catcher. But that is a "belt and braces" approach if your front dérailleur setup is good.

wongataa

Are the end stops set correctly? Surely if the are the cage would prevent the chain being able to fall off unless you somehow lost chain tension while going over a big enough bump to lift the chain up.

shdaxner

Well I thought they were setup correctly tbh, I am generally OK when it comes to setting them up.

I have just checked and with the rear in lowest gear and in the small ring up front there is literally about 1mm between chain and inside derailleur plate, any adjustment to the limit screws will surely end in rubbing?

Also, if my limit screw was set to low then would it not shift off the ring everynow and then? it has never done that with me, I currently have nearly full use of the cassette when in the smaller ring, except maybe the top two gears which it very slight rubs on the outsite plate of the front derailleur but other than that it is fine.

mfin

You say you were in the little ring but in a quite high gear yeah? Have you checked the chain isn't too long, not that it would cause the problem in itself unless it was way too long, but worth checking as part of the setup.

That 1mm gap sounds about right by the way.

shdaxner

I will defo check chain length cheers..... I can't remember the basic formula for working out how many links it needs to be, any idea?

So on the way home today when pulling away from a junction it did it again, only this time it didn't come off the ring just sort of skipped a few teeth instead, any other thoughts on the cause?

bowdy1987

Could be stretched? How many miles has it done? Is the chainring worn?

luv2ride

This Deda Dog Fang chain catcher might help?
http://www.ribblecycles.co.uk/sp/road-t ... tAodKUoAGw
Got one on each of my bikes, just in case. Seem to work well.

DiscoBoy

Luv2ride wrote:

This Deda Dog Fang chain catcher might help?
http://www.ribblecycles.co.uk/sp/road-t ... tAodKUoAGw
Got one on each of my bikes, just in case. Seem to work well.

I think this type is better, personally:

http://www.wiggle.co.uk/token-tk375-cha ... oad-mechs/

shdaxner

bowdy1987 wrote:

Could be stretched? How many miles has it done? Is the chainring worn?

As far as I am aware (the bike is 2nd hand) it has only done a couple of hundred miles as it was bought as a backup race bike but only used rarely - it certainly looks like a low mileage bike, all the components are in really good condition, jockey wheels are not worn, the teeth on the chainrings still have most of their colour (rather than being silver) and the chain is not in bad nick, how do I check if the chain is stretched?

Does anybody know how I know how many links I should have on my chain? isn't there a basic formula something along the lines of big ring size + largest sprocket size + so many to get the number of links?

mfin

Put it in the little ring and smallest sprocket and take a photo, then put it in the big ring and largest sprocket and take another then post them up, you'll get an answer straight away as to whether it looks about right or not.

Past that you'd have to have a lot of chain wear and chainring wear for it to really start playing up due to that. Check for daft stuff like whether all the chainset bolts are nice and tight and everything is turning true while you're investigating too.

Also, check the height of the front mech, photo will tell on that too.

I'm sure with a few of these checks and some photos that a few things can be eliminated.

PS. A basic chain wear tool is cheap and handy to have... http://www.chainreactioncycles.com/s?q=chain+wear

Bobbinogs

shdaxner wrote:

Does anybody know how I know how many links I should have on my chain? isn't there a basic formula something along the lines of big ring size + largest sprocket size + so many to get the number of links?

This website works well:

http://www.machinehead-software.co.uk/b ... hcalc.html

You will need to measure the chainstay (centre rear axle to BB) but it only takes two ticks. The old school way is to wrap the chain round big/big without the rear derailleur, and add 2 links (something like that).

EgasaC

Out of the saddle and pounding the pedals and chain slippage. Only ever happened to me twice. Didn't know what the problem was the first time. It two was, of course, a worn big chainring. Replaced and problem solved.
Next happened at the bottom of Hardnott. Fell off and immediately thought, "shoot, a worn small chainring with this beast to conquer. This'll be fun". It wasn't.
Replaced small chainring at earliest convenience. Problem solved again.

Replace your chainring. It's more worn than you think.

I think.

redvee

DiscoBoy wrote:

I think this type is better, personally:

http://www.wiggle.co.uk/token-tk375-cha ... oad-mechs/

KREX Chain Drop Catcher off Ebay if you're patient.

ai_1

Just a thought but is there any possibility the rear derailleur isn't tensioning the chain enough or smoothly. Perhaps a damaged spring or dirt/corrosion in one of the hinges.

rolf_f

DiscoBoy wrote:

Luv2ride wrote:

This Deda Dog Fang chain catcher might help?
http://www.ribblecycles.co.uk/sp/road-t ... tAodKUoAGw
Got one on each of my bikes, just in case. Seem to work well.

I think this type is better, personally:

http://www.wiggle.co.uk/token-tk375-cha ... oad-mechs/

The Token one isn't very good - those little slots in it means it can flex. I had one and the chain had a remarkable ability to squeeze past the catcher which was tricky because I then had to get the chain back on past the catcher which was still perfectly aligned! I replaced it with one without the slots (a Raleigh one for about £6) and that is fine.

I think the Dog Fang is better though if it actually fits on your frame. No chance of this sort of problem occurring and you can tweak the vertical positioning of it. But if you like bling there are no fancy colour options!

dombo6

Definitely sounds like a worn chain ring. Mine did the same - possibly because i nearly always ride around on the 39. It would jump off, luckily to the granny as I ride a triple, whenever I put power down on a hill, and then even when starting off from standstill. Eventually I changed everything, chain, cassette, middle chainring. Bike now feels like new.

DKay

The Dog Fang won't fit a lot of carbon frames, as you can't get it low enough on the seat tube before it flares out to meet the bottom braket. I had this exact problem when I bought one to fit my Cayo Evo.

Initialised

Chain length should be enough that it can move freely on smallest ring-smallest sprocket and long enough that it can fit around the biggest ring-biggest sprocket.

Check the low limit is correct, check derailleur alignment, check if the cage is bent, check for chain wear and wear on the rings.