Chain dropping off chainring

[Sam Kennedy]

Sometimes when I have stopped, and kick the pedals back, the chain drops off the chain ring, and only in a certain gear. It is a nuisance, especially today when I had to put the chain on 3 times in a row.

What is causing this? A dodgy jockey wheel?

The front mech is Sora, and the rear mech is Tiagra, the shifters are 8 speed Sora.

Any help will be greatly appreciated

 

[accountantpete]

Chain too slack?

 

[Ian H]

Possibilities might include: chain worn, or too long (hence slack, as above), stiff link, extreme chain-line.

 

[twentysix by twentyfive]

Which sprocket / chainring combo is the problem? It could just be that the chain has been dragged quite out of line in that combo so that "back pedalling" results in a misaligned chain. Forwards the mechs will keep it sorted.

 

[Sam Kennedy]

It is when I am in the Big Ring x Big Sprocket. It`s easier to start like that, rather than having to shift to the small ring. (It`s a double)

 

[Ian H]

It is when I am in the Big Ring x Big Sprocket. It`s easier to start like that, rather than having to shift to the small ring. (It`s a double)

Yup, that would cause it.

 

[adscrim]

It is when I am in the Big Ring x Big Sprocket.

There's your extreme chain line. But rememeber that it may be a combination of the factors suggested above.

As a rule of thumb and for the avoidance of excess chain wear caused by extreme chain lines, I try to stay out of the two largest rings on my cassette when in the big ring and vice versa. To make this more managable I replaced a 12-25 cassette with a 11-23 (with a 50/36 compact double). Depending on circumstance, you may not be able to swap cassettes or it may not be a good idea depending on age and ambition. If you are young enough to race as a junior, and if juniors still use junior ratios, I'd contemplate upping cadence and not alway starting in the big ring.

Go to a gear calculation website and enter your variables. From here you can work out what you need to do in order to double shift into the next gear up. For example, when going up the gears, when I shift into the big ring at the front I know I need to move up three on my cassette to get to the next gear. Knowing what ratio to move into makes double shifting a little more practical.

 

[twentysix by twentyfive]

If you don't want to fiddle with your gear ratios it might be possible to fit an adjustable bottom bracket which will allow you to move the chainrings closer to the frame and thus reduce the out of line-ness. This means that you'll already have to have something of a gap between the chainrings and the frame to make going that route worthwhile. Personnaly I'd set up correct gearing so that BigXBig isn't neccesary. I'm afraid so called compact chainsets push one in that bigxbig direction. Triples are better if you need a large range of gears.

 

[I am Spartacus]

Yes ... a chain out of line won't help in any way .. not bike friendly.. and certainly that extreme .. you going to have to suss out your gear limits for each size chain ring.. you probably will have 10 out of 16 or so user friendly gears to play with. replacing BB to a narrower one may give options as well.
Such is a learning curve as they say.... has someone said stay in big ring .... for ever and ever...??

 

[swee'pea99]

It is when I am in the Big Ring x Big Sprocket. It`s easier to start like that, rather than having to shift to the small ring. (It`s a double)

Sorry, but why? As others have said, there's a fair consensus that Big -> big & Small -> small are combinations best avoided. When I used to ride a geared bike, my routine was to always flick onto the small ring before stopping at the lights, leaving the back on the second or third sprocket. I never found it hard. Might it be easiest just to get into a new habit?

 

[Sam Kennedy]

Im just going to go no lower than Big Ring x Second Sprocket. There is just one short sharp hill I need to go over (about 30 foot long, but steep), and thats it.
I can handle most hills in the big ring

 

[iLB]

Im just going to go no lower than Big Ring x Second Sprocket. There is just one short sharp hill I need to go over (about 30 foot long, but steep), and thats it.
I can handle most hills in the big ring

you'll be needing to find some real hills then, or new knees in a few years

 

[twentysix by twentyfive]

What's wrong with the little ring? It's there for a purpose