Changing front crank from 2 rings to 3.

[Mattavelli]

Hi guys,
I'm currently fixing up a friend's bike and his front 2 ring chainset was knackered so he decided he wanted to change it for a 3 ring.

I bought a Shimano Alivio front crank (3 rings). The front trigger shifters had 3 pre-sets already so i assumed it would be a simple swap. However, i'm having problems setting the front derailleur: the jump from the inner most ring to the middle is way too high - it goes from inner to outer and i can't get it to smoothly fit on all three.

Am i missing something here?

Thanks,
Matt

[nfmisso]

The 3 position trigger shifter has to match the spacing of the rings; if you got 8 speed rings you need an "8 speed" shifter, etc for 9, 10, ...

Sounds like you are trying to use a 7 speed shifter with 9 speed crankset, or similar.

I prefer to use straight friction for the front, then if the shifter has enough cable travel, no problems. So an older 5 speed (aka 15 speed) front friction shifter will work fine because it has plenty of travel.

[Mattavelli]

Hi Nigel,

Thanks for your reply. So to confirm: I'll need a new shifter? The back set is an 8 speed and the front is now 3.

[nfmisso]

Hi Matt;

Yes. You need to know what the front was intended to go wit, if recent: 7/8, 9 or 10 if you are going with a "click" shifter.

For example this set is for 7/8 speed:
http://www.amazon.com/Shimano-FC-M410-Alivio-8-Speed-Square/dp/B000GGV1V0/

this one for 9:
http://www.amazon.com/Shimano-Tiagra-9-Speed-50-39-30t-Crankset/dp/B001GSQNL0/

and this one for 10:
http://www.amazon.com/Shimano-M780-Triple-175mm-Crankset/dp/B0050OG1UO/

[DaveM]

You may also need a different front derailleur. Derailleurs for triple cranks are different than for double. You might try this before buying a whole new shifter set. But you may need both depending on the combination of parts.

[Mattavelli]

Thanks for all the replies everyone - as always, the help is greatly appreciated.

I found an old twist shifter and it seems to have solved the problem somewhat. It's still not perfect but the shifter isn't that great (the cable pulls out of position at the shifter end).

I've got a spare Deore front derailleur to see if that improves things.

Thanks again!

Matt.

[nfmisso]

(08-11-2011, 08:28 AM)DaveM Wrote:  You may also need a different front derailleur. Derailleurs for triple cranks are different than for double. You might try this before buying a whole new shifter set. But you may need both depending on the combination of parts.

I do not think that this is the case here, because he says that it will go to the smallest and largest ring okay, just will not go to the middle nicely with the click positions.

[DaveM]

(08-11-2011, 07:55 PM)nfmisso Wrote:  

(08-11-2011, 08:28 AM)DaveM Wrote:  You may also need a different front derailleur. Derailleurs for triple cranks are different than for double. You might try this before buying a whole new shifter set. But you may need both depending on the combination of parts.

I do not think that this is the case here, because he says that it will go to the smallest and largest ring okay, just will not go to the middle nicely with the click positions.

Sounds like you were right.
It's tough to get good shifting on a triple with a double der, but the OP's main issue was the shifter.