Chain scraping front derailleur

Mr Velo

Gentlemen/Ladies....

I have an annoying problem whereby my chain scrapes against the front derailleur....
I have a triple wheel crank - and this only happens once i'm in the biggest wheel - and go towards gear 7 or 8 at the back....
It's more annoying than anything else. Any ideas what may need adjusting to stop this from happening?

Thanks.

rflynnr

If you're going that far back on the cassette whilst sitting in the big ring then some chain rub is almost inevitable: the best set-up derailleur in the world won't permit that much flexibility. If you find you're going into the bigger gears at the back you need to move into the smaller chainrings at the front.

Mr Velo

Thanks for that. Think i'll put up with the noise then - couldn't cope with having to go higher down to mid wheel and low at the back....

LastGasp

You should find a good compromise gear that suits you by staying in the middle chainring at front, and around the middle at the back, but going to bigger back cogs for uphill, and smaller for downhill. Then the big ring at the front can be reserved for good downhills where you really want to get up to high speeds, and the "Granny" ring at the front for climbing steep hills. You should not use the big chainring with the biggest 2 (or so) cogs at the back, and you should not use the small chainring with the smallest cogs at the back. Apart from the noise, your chain is not running in a straight line, which causes additional wear on the chain, chainrings and back cogs, and of course the extra friction generated in the whole drivetrain makes pedalling harder !

rottenhat

With due respect, you should probably learn to use your gears properly. what you are doing is known as cross-chaining and puts unnecessary wear on your chain and cassette. It is not that hard to learn to shift down at the front and up at the rear more or less simultaneously.

davey101

eh! excuse my ignorance but can he not just adjust the derailer so that there is no chain rub.
I had the same problem and got it sorted handy enough by slight adjustments. if you dont know how to adjust the derailers look on youtube you will find a good example there

DirkVoodoo

Which is gear 7 or 8? Little or big sprocket?

If it's not cross chaining and rubbing when you are in the big front ring and little back cog, then you need to loosen your upper limit screw a tad (not too much or you risk pushing the chain off).

If gear 7 or 8 (?) is a big cog, then like they say you are using the gears incorrectly. All combinations are selectable but not all of them are usable.

griffin100

this might help.

http://www.boards.ie/vbulletin/showthread.php?t=2055615936

davey101

DirkVoodoo wrote: »

All combinations are selectable but not all of them are usable.

Dirkvoodoo could you explain this please, sorry but i dont quite get what you mean. I always thought that any combination of gears was useable, at some point.
Thanks

Lumen

https://www.youtube.com/watch?v=24vfX2PtSMM

penexpers

davey101 wrote: »

Dirkvoodoo could you explain this please, sorry but i dont quite get what you mean. I always thought that any combination of gears was useable, at some point.
Thanks

If you use the big chainring with the biggest cog and then, say, change down to the middle chainring, there's a good chance your rear derailleur will end up in your spokes. This has happened me twice.

Generally big-big combinations should be avoided for this reason.

rflynnr

davey101 wrote: »

Dirkvoodoo could you explain this please, sorry but i dont quite get what you mean. I always thought that any combination of gears was useable, at some point.
Thanks

I think Dirk means that whilst it is possible to put the chain around the big chainring and the biggest cog at the back simultaneously, the (almost) inevitable chain rub on the derailleur will make it difficult to actually pedal with that combination. At best you're going to get a lot of noise and at worst you will eventually destroy (not degrade but actually destroy) both the chain and derailleur. This kind of problem will be more acute for triple ringed bikes but even on my double I can't get into the 3rd largest cog at the back (on a 10-speed cassette) if I'm in the big ring.

Think Ghostbusters: "Don't cross the streams. It will be bad."

Mr Velo

Ok, sorry i didn't explain myself correctly.

I normally cycle in the big ring (at the front) all the time. I have a 9 ring cassette at the back, i count the biggest ring at the back to be gear 1 - the smallest to be gear 9. Generally i'm and around gear 5 or 6 when out on the flat etc.

It's when it comes to a sprint etc where i go into gear 8 or 9 at the back - and staying in big ring in front - that's where the friction agains the front derailleur occurs.

Thanks for the advice thusfar however. I have now learned that i should never climb whilst in big ring at the front - drop down to middle ring and find a suitable ring at the back to climb with.
Never heard of cross-chaining. You learn something new every day.

LastGasp

Ah right so.... forget all that other crap we've been telling you, and adjust the stop screw on your derailleur to get another mm or so of travel, but not so far that the chain comes off the outside ! I'm sure some of the others will give a more accurate instruction, complete with pics !

Lumen

Excessive detail attack!

davey101

Lumen wrote: »

https://www.youtube.com/watch?v=24vfX2PtSMM

now that makes a lot of sense cheers Lumen. I have noticed the large angle thats created before but thought nothing of it as i did see others doing the same thing. this may explain why i broke a rear axle on a brand new bike during the summer climbing some nasty hills.
And i thought i was just Savage!:rolleyes:

cdaly_

It's also worth noting that some shifters allow you to click the release lever once and move the derailleur a small amount. Not enough to drop to the middle ring but enough to stop clicking.

Of course you first have to adjust the high limit screw to allow enough movement to the right.

DirkVoodoo

davey101 wrote: »

Dirkvoodoo could you explain this please, sorry but i dont quite get what you mean. I always thought that any combination of gears was useable, at some point.
Thanks

Sorry, what I was trying to say is that a bike drivetrain is designed in such a way that gears you should not ride with (cross chaining, excessive drivetrain wear, rubbing, general unpleasantness) are still selectable. Just because you can still choose it (I would imagine some complex dual-chain, dual derailleur setup or more simply a hub gear system would solve this) it doesn't mean that you should select it.

Derailleur systems have a lot of overlap, especially on a triple setup so there is no need to crosschain. If you are cross chaining and experiencing rubbing, you are just in the wrong gear.

DirkVoodoo

cdaly_ wrote: »

It's also worth noting that some shifters allow you to click the release lever once and move the derailleur a small amount. Not enough to drop to the middle ring but enough to stop clicking.

"Trimming"