Is it possible to use a triple front mech with a double ring crank? I’m building up a bike and have got a double XT chainset to go on it (40-28t), and I need to get a front derailleur for it. But I might want to swap to a triple chainset if the double doesn’t give me enough range (I’ve ordered an 11-36 cassette, hoping that will get me low enough with the 28 on the front).

Will the triple derailleur work with the double rings? That will future proof me, if I do decide to change. I’m guessing a double derailleur won’t have enough travel for a 3 rings, so I’d end up buying another one of them as well.

yes

Isn’t the ring spacing slightly different on a double ring specific crank, meaning you need a double ring mech?

i use a triple one on both road and mtb with a double setup, you just have an extra unused click.

Can’t be. My SLX shifters have a switch to go from 2 to 3 speed. I doubt it’s complicated in there to change the shift amount, just limit the movement.

(I might be very wrong and therefore impressed with Shimano)

Not sure about those ring sizes – but I found triple mech wouldn’t work usably with a latest model XT 26:38 double.

Original setup was 10spd triple XT mech, shifter and chainset.

The latest Shimano mech cage shapes are very ring / chainline specific. I couldn’t find a position or alignment where the triple front mech didn’t have some kind of problem (rubbing chain at one or other extreme of rear cassette or fouling cage on rings etc). Gave up and bought a double specific mech and it set up fine first try.

No problem with the shifter – just an unused click (ours was a shifter prior to the 2-3 speed setting switch thingy).

If you are using a std triple chainset with one ring removed(or double and bash) then yes,but the newer design double shimano cranks have a different spacing which is why you have the option to select 2 or 3 rings on the newer shifters.

Been doing that on my road bike (triple to compact) for years with no problem, and thats a bigger jump in chain ring sizes.
Just need to set the limit screws right and ignore the extra click.

^^^wot Brassneck said – I have been doing the same with no problem

Been doing that on my road bike (triple to compact) for years with no problem, and thats a bigger jump in chain ring sizes.
Just need to set the limit screws right and ignore the extra click

I’ve also been doing it for years – but the newest combos just don’t work (certainly in 26:38 double specific chainset NOT just taking a ring off a triple). The spacing and shape of the cage is very specific (damn you Shimano)

I guessed the ring spacing might be different, but that’s all taken care of by the indexing in the shifter (and the switch to select 2/3). The mech doesn’t have any indexing does it? So it shouldn’t really care if the spacing is different, it just moves the amount the shifter tells it to. But I guess there may be differences in the shape/size of the cage. Probably not worth taking the risk if that’s the case then.

Probably not worth taking the risk if that’s the case then.

I’s have thought it was worth taking the risk – what’s the worst that can happen? – it might not work. Nothing lost really

Triple might work on the 40:28 chainset. It didn’t on the 38:26.

The gap between the cage plates is contoured.

If the triple mech was positioned to clear the chainrings, then the chain rubbed on one or other of the cage plates – depending on which gear you are in at the rear as the chain entry angle changes (adjusting indexing just changed which plate it rubs).

Adjusting the mech height up/down so chain didn’t rub the cage meant the mech fouled the chainrings or the chain rode off the top of the outer ring.

With HT2 bbs, the chainline is fixed and shimano have fiddled with the mechs to match them. So you are also in a different bit of the intended parallelogram arc if running the wrong mech / chainset combo.

Have a look at pictures of the double and triple specific front mechs on Merlin etc – the cage lengths and shapes are different.

Sack all this and bring back old style mechs and micro index friction front shifter 🙂

I’s have thought it was worth taking the risk – what’s the worst that can happen? – it might not work. Nothing lost really

What he said. I’d definitely be riding it before shelling out for a new mech. front shifting is always a bit agricultural anyway.

I did this with my SLX mech at Xmas. Just replaced the old triple crankset with the new double and wound in the HI screw on the mech. Works fine. This is a 2013 bike and running gear as well.

I don’t have any much at the moment to try it with – it’s a new bike I’m building up. I have to buy a front mech either way. I thought a triple would give me an upgrade path if I later change to a triple chain set.

What a load of tosh some people have been talking on here.

1. Spacing between rings on a double and triple is exactly the same.
2. Front shifters pull 11mm of cable with the first shift (small to middle) and 7mm of cable with the second shift (middle to large). This is the same with Shimano, SRAM, 9sp and 10sp, they’re all interchangeable.
3. Shimano’s 2×9 mechs needed 11mm of cable pull so used the first shift. Their 2×10 mechs need 7mm of cable pull so use the second shift. That’s all the 2x/3x switch does on the 2×10 shifters, it forces you to use the second shift.
4. A 3x mech will work perfectly well with double rings so long as you don’t try and move it closer to the middle ring. That will put the chain/rings in the wrong part of the cage, and make you use the second shift, which will muck up your shifting. All you need to do is leave it where it was for your 3x setup, wind in the limit screw to stop you trying to shift into the non existent big ring, and take a few links out of the chain if you wish.

Great answer from Perth MTB there, respect for your knowledge.

I got to this thread from a search for another question – will a 7\8speed front mech work for 9speed? I suspect yes but a little confirmation would be ace, any thoughts?

Andy

IME it will work, but maybe not brilliantly.