what causes this

pingpong

Brand spanking new bike, only trouble is when tha chain is on the small front chainring and the smallest sprocket at the back, the outer chain plate is rubbing on the inner front large chainring. Ok I am sending the bike back, but just for interest what would cause this to happen.....I am only glad I have got another bike to play with

rohloff-rich

Don't send the bike back for this - you're not really supposed to use small front + small rear (or large front + large rear), the chain and drivetrain isn't designed to run in every single gear combination.

Johnny Ergo

Sometimes you can fix this by adjusting the lower limit screw on the front mech - but I wouldn't advise this if you're not sure what to do.
As Rohloff-Rich says, dont send it back for this. It's just an inherent fault with triples that the chain can't run clear of front mech cage in all combinations. Depending on how many teeth you have in chain rings and sprockets you will will find similar gear on the middle chainring on about third, fourth or fifth sprocket.
Good luck.
Johnny

PS - If you're not sure take it to your local LBS to adjust. At least it will reduce your carbon footprint sending the bike all over the country

JustRidecp

Dont know what bike/groupset you have but take a look at this document, from the shimano technical document website - its for 105 triple front mech.

http://techdocs.shimano.com/media/techdocs/content/cycle/SI/105/FD-5503-5504/SI-57Z0C-En_v1_m56577569830603724.pdf

its got a wee picture and info telling you what gears will cause interference, etc.

Also, for future reference, you can get service manuals for all shimano components from their website.

pingpong

Thanks for the reply, tto be quite honest I am having a little problem with the front mech, the chain is rubbing when in the small front chainring and any of the 3 smallest sprockets .Frustrating more than anything. I have tried all sorts of adjustments, but to no avail..think I will give up and go for a pint :?

pingpong

Sorry it's a Ultegra compact double,and I cant op :x en that shimano link you gave me.......what a day I am having who needs holidays???

rohloff-rich

pingpong wrote:

Thanks for the reply, tto be quite honest I am having a little problem with the front mech, the chain is rubbing when in the small front chainring and any of the 3 smallest sprockets .

Read the above again - you're not really supposed to be using that kind of gear ratio! Rub in that kind of gear is not all that uncommon!

JustRidecp

pingpong wrote:

the chain is rubbing when in the small front chainring and any of the 3 smallest sprockets .

Hey, dont worry about this. This is a gear combination that you're not really supposed to use and WILL cause chain rubbing. Similar things happen in biggest chainring on biggest sprockets. In both of these combinations, the chain is being stretched laterally to its full extent. Riding in any of these combinations will cause you to wear out your chain very quickly. No amount of mech adjustment will fix this. Unfortunatly if a bike is said to have 27 gears, this doesn't mean 27 usuable gears!

For the shimano tech documents try following this

http://techdocs.shimano.com/techdocs/index.jsp

the link for ultegra front mech is

http://techdocs.shimano.com/media/techdocs/content/cycle/SI/SI_5JD0A_001/SI_5JD0A_001_En_v1_m56577569830616200.pdf

I've checked these links and they should work. You'll need adobe acrobat reader to view the pdf

Pagem

as others have said; you don't want to really use the smallest chainring and the smallest cog together and vice versa. this is called 'cross chaining' and is a real no-no.

i notice that you are running an ultegra groupset. although you'll still get a rub on the smallest rear cog you should be able to get away with no rubbing in the other two cogs whilst in the small front chain ring. on the lever, when you've knocked it down to the front chain ring there is a setting which allows you to move the front cage over just a touch - this will stoop some of the chain rub. basically you press the gear lever as if trying to change up to the large chain ring but gently. you should feel an intermediate resistance and the cage will have moved a few millimetres to the right. it will stay there unless you knock it down by flicking the gear lever which normally shifts you into the little chainring. capasa?

however, as said - avoid cross-chaining...

pingpong

Thanks for that, my turn to give blood today, so I will have a go a little later. Thanks again

McBain_v1

First, I'd say you shouldn't be running that sort of combination, it's bound to cause some chain rub and ultimately excessive wear on the chain and chain rings. Second, the Ultegra does allow you to "feather" the front derailleur to allow some adjustment (I think the Dura-Ace does as well, I'll give it a go tonight) but it isn't the solution really.

Be a man and go for the big outer ring