Front derailleur for a double chainring set up?

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Front derailleur for a double chainring set up?

12 posts & 7 voices | Started 11 months ago by mtbtomo | Latest reply from TurnerGuy

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mtbtomo - Member

So I've fitted a 27/39 double chainset to my bike.

I've adjusted the stops to minimise how far it can move the chain, and still using a 3 spd shifter, but using just two clicks it seems a bit easy to sling the chain right over and off the outer chainring.

Would a derailleur specifically for a double chainset prevent this? Would I also need a new shifter?

Also, do double front derailleurs sit closer to the chainring? The existing one sits a long way from the chainring, presumably because it would normally be used with a bigger outer ring. I can't lower the existing derailleur because its a direct mount one.

Posted 11 months ago #
Bez - Member

Your 'H' screw is right in, I assume? If not, the obvious solution is screw it in more. I've not had a problem with the stops on Shimano mechs being insufficient for just two rings.

Posted 11 months ago #
mtbtomo - Member

The 'H' screw is right in.

I might have pulled the cable too taught, so essentially from small ring to big ring, the whole shifting range is further outboard?

I just wondered if dedicated dual ring derailleurs are any easier to set up? And also if they run closer to the outer chainring i.e. like the usual ~2mm gap from a 44t outer ring but for a 39t. Currently the gap on a 39 is massive and I can't get the mech any lower.

I'll persist with the cable adjustment.

Posted 11 months ago #
jim_bob - Member

I have an SLX dual-ring front mech. It seems to have a tighter curve to follow the smaller ring.

Mine is standard not direct-mount, so getting it at the right height was just a case of setting it in the right position on the seat tube.

Posted 11 months ago #
mtbtomo - Member

Does anyone know if one of these fit my Zesty, and also work with a 3 spd (X9) shifter?

I'm having problems with my existing mech firing the chain over the outer ring. Would a bash ring help prevent this and does anyone do a vaguely XC one for a 39T outer?

Posted 11 months ago #
ruscle - Member

Problem is these stupid new standards such as direct mount mech's and press fit bottom brackets, all roadie stuff that isn't needed on a MTB and makes life harder. I'm doing a similar conversion, was told to leave the front mech high up as will aid shifting for some reason, also if the 'H' screw needs to be longer purchase a longer one from local hardware shop and fit, this will solve your problem and be cheap.

Posted 11 months ago #
mtbtomo - Member

Yep...I have a max of about 5mm adjustment on the derailleur height cos thats how long the slots are in the mech.

I didn't think running 27-39 would be too dissimilar from just ditching an outer ring and running a double and bash...???

I get the feeling that lowering the mech or using a double specific would decrease the likelihood of the chain dropping off on the inside when changing down? Which has also happened.

Good point on the adjustment screw, will source a longer one to start with!

Posted 11 months ago #
njee20 - Member

Yes if the chain can still move over the outer ring your stop screw needs adjusting, so get a longer one. Try your LBS, they will probably have a pile of old mechs to raid. Then it should work perfectly with your existing mech.

Posted 11 months ago #
mtbtomo - Member

Thanks guys, longer screw first stop!

Posted 11 months ago #
coatesy - Member

And just to confuse matters further, i'm pretty sure Lapierre aren't a direct mount(even though they mount directly), but an e-type with the BB mount removed.

Posted 11 months ago #
mtbtomo - Member

Yes, I had a look at Shimano mech's and it does seem the only ones you can get are E-type with the mount to be removed. So that's different from proper 'direct mount' is it?

Posted 11 months ago #
TurnerGuy - Member

I have 27-40 and managed to lock down my XTR front mech enough to work fine.

Posted 11 months ago #

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