Front derailleur question

[citybabe]

I've changed my chainset from a 26-36-48 to a 22-32-44. The chain is now rubbing on the front derailleur and it wont change down onto the small chainring. Do I need to adjust the derailleur or should I have added a spacer or two?

 

[MrJamie]

Id guess that the sprockets are smaller and that the derailleur probably needs its height realigning for that anyway if nothing else. Im sure someone who knows what theyre talking about will be along soon though

 

[Andy_R]

What chainset did you put on and where is the chain rubbing the mech?

 

[RecordAceFromNew]

It is possible your chainline is wrong (has decreased) - it is worth measuring it. If it is not more than a couple of mm out from 47.5mm then you could put the front gear on the big ring and then back the L limit screw of the front mech out before trying again to see if it is better. If not you will need to make some changes and to assess will need the make/model/dimension of the old and new chainsets and bottom brackets.

If backing out the L limit screw works it is worthwhile to set the front mech up properly if you haven't already. By switching from a 48T large to 44T large, you need to move the front mech down the seat tube by at least 8mm. For an excellent guide on front mech setup see this.

 

[Pauluk]

Just a question to the more knowledgeable, I can understand why the front derailleur would need adjusting to a lower position but wouldn't the chain need some links removing also with the reduced size front sprocket.

 

[RecordAceFromNew]

wouldn't the chain need some links removing also with the reduced size front sprocket.

If that hasn't been done already, and if the chain is slack on small / small, and if it is the original chain then it needs to be shortened by 2 links (one pair). Otherwise there are some advantages in running a chain that is longer than the minimum if rear mech allows. The weight penalty of 2 grams a link is often a small price to pay since it is trickier to lengthen than to shorten a chain, and it is handy to have spares when chain gets chewed / has stiff link or when one needs a lower geared cassette / wheel etc.

Chain length is not the cause of the OP's present problem.

 

[citybabe]

Just a question to the more knowledgeable, I can understand why the front derailleur would need adjusting to a lower position but wouldn't the chain need some links removing also with the reduced size front sprocket.

I realise that two links need to come out which I'll do once the chain rubbing is sorted out

 

[citybabe]

What chainset did you put on and where is the chain rubbing the mech?

It's a Shimano Deore M590 triple and it's rubbing on the inside or the derailleur the side that's attached to the seat post

 

[Pauluk]

if it is the original chain then it needs to be shortened by 2 links (one pair)

Sorry to labour the point but I'm trying to learn about bike mechanics. Theoretically, shouldn't the chain length length be reduced by 2 pairs (4 links) as the sprocket has gone from a 48 to a 44.

 

[Andy_R]

When you installed it, what spacers did you use? You need 5mm of spacers on the drive side and 2.5mm on the non drive side

 

[RecordAceFromNew]

Sorry to labour the point but I'm trying to learn about bike mechanics. Theoretically, shouldn't the chain length length be reduced by 2 pairs (4 links) as the sprocket has gone from a 48 to a 44.

No problem Pauluk. It is tempting to see it that way, but since we are not talking about a chain wrapping around one sprocket but two, the way to visualise it, is unless the two sprockets are very different in size and the chainstay is very short, half the teeth (the ones facing the other sprocket) are not making any difference to the chain length at all. Hence for bicycle chain length estimation purpose every 4T for two (one pair of) links is generally an excellent approximation.

To test the above you can also play around with a chain length calculator.

 

[RecordAceFromNew]

When you installed it, what spacers did you use? You need 5mm of spacers on the drive side and 2.5mm on the non drive side

Most likely correct, though it does depend on the bike/configuration, and what it is replacing.

 

[Andy_R]

Most likely correct, though it does depend on the bike/configuration, and what it is replacing.

I'm basing it on a standard 68mm shell and a non oversize seat post tube, obviously this may not be the case

 

[citybabe]

I haven't used the spacers.
When I did put it together using the spacers the left hand crank wouldn't fit onto the bike so I took them off.

 

[citybabe]

Most likely correct, though it does depend on the bike/configuration, and what it is replacing.

I see I should be using the spacers as I have a 68mm bottom bracket.
I'll take it apart and fit the spacers somehow