Chain coming off

Alibran

I've had my new road bike, a Trek 1.2 WSD, for over a month now, and I keep having problems with the chain coming off. It's been back to the LBS three times, and every time they've checked it and said the indexing is fine, and tactfully suggested it might be down to me being a bit rough with it. Is this likely to be correct?

If it's going to come off, it happens when changing from the middle to small chainring (it's a triple), and it will happen when changing under a very slight load. If I stop turning the pedals, move the STI lever and then just spin them gently, I can be confident it won't come off, but I lose a lot of momentum doing that. I've never changed gear under much load because my old Apollo hybrid just wouldn't do it, but I know my legs have got a lot stronger in the last couple of months or so, and I could be putting more pressure on than I realise. Is this likely to be the problem, or could there be something mechanical that the staff at the LBS are missing?

feel

The little "L" screw on the deraileur which limits the amount of movement might need a small amount of adjustment.

Edit This LINK might be useful

wilkies80

check out the videos on youtube about bike servicing, and do it yourself. you might get it sorted and you'll give yourself a sence of achievement.

Alibran

Well, I've had a look at the link in feel's post, and that seems to make sense. I'm at work today, but I'll have a go at adjusting it tomorrow before my ride, and see how I get on.

CrookedCucumber

I don't know what other folks think, but I'm not at all convinced that being rough when changing ought ever to bring the chain off. It sounds more like a problem with the derailleur limit stops to me.

Max_Man

CrookedCucumber wrote:

It sounds more like a problem with the derailleur limit stops to me.

Thats what it sounds like to me too but 3 times in a LBS, surely the limit screws would have been set right.

I don't think being rough has any bearing on this, the derailleur only moves from point A to point B.... :?:

acorn_user

I might buy the being rough theory. If you change at the wrong time, you will drop the chain, even if the bike is set up right. Are you already in one of the extremes at the back when you change the front? That might be something to do with it.

Alternatively, another possibility would be a bent chain. I'ld have thought the mechanics would have seen that.

Good luck!

Alibran

acorn_user wrote:

I might buy the being rough theory. If you change at the wrong time, you will drop the chain, even if the bike is set up right. Are you already in one of the extremes at the back when you change the front? That might be something to do with it.

Yes, I usually am. I don't tend to change to the small ring at the front until I've run out of gears at the back. However, while we were out today (having not tried to adjust it before we left because I forgot), I was chatting to my partner, and changed under load with the chain near the middle at the back. Had an "oops, shouldn't have done that" moment before I realised the chain was still on. So there could be something in what you're saying. I'll experiment a bit.

Swannie

A friend has a little plastic gadget on the seat tube by the derailieur.

It is shaped like a small claw, and it stops the chain from travelling past the smaller ring. Otherwise, the loss of tension on the front can be so strong, as to throw the chain off. Seems this little claw/chain saver, whatever, stops the chain from jumping if it's a rough change.

If it was me, I'd be playing with my shifting, and if that didn't sort it, I'd be looking at a new front mech.

gkerr4

could the inner-most chainring be damaged in some way - does it look straight - I had an old MTB with a triple front chainring - the inner ring was damaged and changing under pressure would result in the chain coming straight off!

CrookedCucumber

Funny how things work out... after saying that I didn't think that poor shifting could cause a chain to come off, I saw exactly that this morning, for the first time.

My 9-year-old daughter has a brand new bike, and it's her first with a front derailleur. I'm sure the chain is OK, and I've checked the derailleur limits myself, even though I had no reason to think the shop (a decent one I've dealt with my times) hadn't done it properly.

Coming up to a hill, she changed the front ring when she meant to change the rear, and with the pedals stationary. Then she stood up on the pedal and pressed with all her strength. The chain came off front _and_ rear, and it was a devil to unjam it.

So I'm inclined to retract what I said earlier -- I think that bad shifting probably can cause a chain throw. But, with the greatest respect to my daughter, this was really incompetent shifting

redddraggon

Alibran wrote:

Yes, I usually am. I don't tend to change to the small ring at the front until I've run out of gears at the back. However, while we were out today (having not tried to adjust it before we left because I forgot), I was chatting to my partner, and changed under load with the chain near the middle at the back. Had an "oops, shouldn't have done that" moment before I realised the chain was still on. So there could be something in what you're saying. I'll experiment a bit.

You shouldn't leave until the end of the cassette to shift, for a start you are making a really bad chainline causing more wear on the chain and cassette and it's probably contributing to the chain falling off after shifting down at the front.

DavidTQ

Max_Man wrote:

CrookedCucumber wrote:

It sounds more like a problem with the derailleur limit stops to me.

Thats what it sounds like to me too but 3 times in a LBS, surely the limit screws would have been set right.
I don't think being rough has any bearing on this, the derailleur only moves from point A to point B.... :?:

Dont bet on it... The main reason the bikeshop I brought my hybrid from didnt get my business for the road bike was because their mechanics were useless. The chain was jumping off the inside swapping to the smallest front cog when I brought the bike, I took it back got it fixed (runing but still not smooth when it came back) then took it in for the 6 week service it came back again with the gears jumping off the inside cog at the front, it took me a whole 5 minutes with the haynes manual to figure out which screw to turn to stop it happening and get it running better than they ever did...

That was a large bike shop that claimed to have 5 mechanics, I guess my bike was put together by the chimp hidden out back whilst the mechanics drank tea...

My brakes were also badly assembled and barely working...

I have no doubt that they may get something to shift with no weight on it but that in practise its not well enough adjusted for use under power,,, I know from my own servicing and adjusting that just because something looks fine on the work stand doesnt mean it will be spot on on the road.

Alibran

redddraggon wrote:

Alibran wrote:

Yes, I usually am. I don't tend to change to the small ring at the front until I've run out of gears at the back. However, while we were out today (having not tried to adjust it before we left because I forgot), I was chatting to my partner, and changed under load with the chain near the middle at the back. Had an "oops, shouldn't have done that" moment before I realised the chain was still on. So there could be something in what you're saying. I'll experiment a bit.

You shouldn't leave until the end of the cassette to shift, for a start you are making a really bad chainline causing more wear on the chain and cassette and it's probably contributing to the chain falling off after shifting down at the front.

I have a triple chainset. I didn't think middle ring to either end of the cassette was a bad chainline. I never go past the middle of the cassette on either the small or large chainring.

Anyway, the problem seems to be solved. I now avoid changing from the middle to small chainring when I'm already in my lowest gear on the cassette (or if I've put myself into a situation where I have to, I make sure it's a very, very gentle change), and the chain hasn't come off since.