Converting triple to double

dazz25

I want to convert my triple to a double as I hardly ever use the top chainring. I'm after some help as i'm not sure what i'll need.

I currently have SLX M670 shifter which has the double/triple switch on the bottom and a Deore M590 crank.

Can anybody offer any advice on the following:

Do I need shorter chainring bolts? If so, which ones? I heard aluminium ones are to be avoided.

How does the switch on the back of the shifter work?

Finally - I've never shortened a chain on a full suss before so is it just a matter of letting the air out of the shock, fully compressing it and wrapping the chain round the 2 biggest gears and leaving 2 links?

Cheers

cooldad

Shorter - yes unless you fit a bash
Switch - no idea, switch it I guess, but all you need to do is use the high limit screw to stop the mech moving to the third position.
Chain - pretty much, if fully compressed is where the chain is longest.

gregwari

Hey

As per cooldad, fit a bash in place of the top ring - it's an easy straight swap out (fit a bash size = to the middle cog, i.e. if your cranks are 22/32/44's, remove the 44T and replace with a 32T bash), plus you won't need new bolts. Once done, put the chain on the bigger of the 2 chainrings and tighten the 'H' screw on the front derailleur so it can't jump off the bigger cog.

In terms of shortening the chain, if you don't currently use the big cog and the chains not causing an issue, leave it as is... you'll have the option of fitting the 44T ring back on at a later stage if you do.

In terms of the switch on the shifter, no idea what that is... it shouldn't need adjusting anyway, only thing that is will be the H screw (high limit) on the derailleur.

rickbst170

I fitted a renthal single ring in the middle of my m770 triple. It was machined so that the standard triple bolts are spaced correctly and didn't need new bolts or bash.

Still drops onto the granny and indexing all good. Pickup from granny to middle is a bit slow, and only works above 4th gear on the cassette, but as the gear ratios are doubled up from 5-10 it's irrelevant.

The Rookie

So you are suggesting a more expensive solution with worse shifting for why?

Sounds like a really dumb idea, single ring bolts are less than a tenner.

rickbst170

Not suggesting it as a solution, just pointing out that not all chainrings require shorter bolts.

I'm assuming the op is buying a new middle ring with more teeth anyway, so the new one might or might not need shorter bolts. If you are not chaining the ring then obviously you will need shorter bolts or a bash.

rickbst170

Having moved from triple to double, I'd not use a single ring in the setup next time. It hold the chain really well and I don't use the granny much but it isn't as good as a ring with guides on.

To be honest, I'm not really gettin on with the double setup. Don't think I'm fit enough. I need a bigger big ring on the downs but couldnt go much bigger than 24-36 on the climbs, so if I made the front into a 40, the granny becomes a 26 so too big. Just feels like a double lacks gears.

cooldad

So easy enough to go back.

rockmonkeysc

rickbst170 wrote:

I fitted a renthal single ring in the middle of my m770 triple. It was machined so that the standard triple bolts are spaced correctly and didn't need new bolts or bash.

Still drops onto the granny and indexing all good. Pickup from granny to middle is a bit slow, and only works above 4th gear on the cassette, but as the gear ratios are doubled up from 5-10 it's irrelevant.

Are you sure you fitted your ring around the right way? Renthal counterbore the holes so that the chain ring bolt head fits flush, effectively making it the same thickness as a standard middle ring.
I have a couple of them and they definitely need short bolts.

rickbst170

The teeth are cut the same either way round but you're right, one side is counter bored. I've fitted it backwards so it's offset. Then I spaced granny to compensate for the protruding nut. Then I just spaced the bb so that chainline and indexing is still spot on. Wasn't a big deal as was part of a build and XT bbs cone with a 2.5, 1.8 and 0.7 spacer so plenty of options when spacing.

It holds the chain tight and used as a single 99% of the time. Only have the granny as a get out of jail ring. Every gear drops in quickly on the cassette, no chain rub, no skipping. Based on that I'd say it works. Just a bit clunky going from granny to renthal ring. Everything else is good.

Think I paid 11 quid for the renthal ring, 10 quid for the m770 crank so didn't fancy shelling out 20 quid on kcnc bolts if not necessary.

rockmonkeysc

That's going to be very weak fitted the wrong way around. There's a big stress riser in that counterbore and it's not going to take much shear load before it fails. There's a good reason why they put in that counterbore.
So you have fitted a ring that will shift badly, put it on wrong and bodged the granny to suit and weakened an expensive chain ring? Good work.

rickbst170

Ask renthal. They say either is fine. But im sure you know more than the manufacture. You seem to know everything, and any disagreement with you make the other person a moron.

The op asked if they have to buy shorter bolts. Why don't you lot answer that, I'm done with this forum.

rockmonkeysc

Goodbye :-)