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wondering about converting my M970 triple chainset to a double.
chainline ok?
any other issues?
better to sell it and buy a middleburn duo?
I phoned middleburn the other day; they don't make rings for this model as I understand it . . .
could just remove the big ring ? m970 is 104 BCD so Middleburn chainrings should fit
and adjust the stop screws to delete the big ring position, fit a bash ring and think about going up to something like a 22 - 36 combo. Shorten the chain a bit too.
You need to get some thin washers to space out the Inner chainring - the spacing is usually built into the XTR rings. This is a unique problem when converting M970s to a double.
Yep, Gee's right, 2mm spacers on the granny ring. Otherwise it's fine!
Yup, spacers on the inner ring to get the right shifting. Also, you'll need a 64mm BCD ring, not a 59mm BCD ring.
Rob
[url= http://www.bigrobracing.co.uk ]www.bigrobracing.co.uk[/url]
I have to ask why. You'll still need front and rear mechs and both shifters.
Why not? I found 28/40 spot on, 22 is useless, 44's a little tall, so go somewhere in the middle!
I got it -- thanks all -- so I need a bash ring as the outer ring? So no real weight savings, then?
Bash or no bash. Its your choice,it will still work. you might need shorter chainring bolts too if you choose the latter
As above, don't need a bash ring. There's not really a massive weight saving (essentially the weight of the ring you remove), do it because you want better ratios, not to save weight IMO.
I agreen -- but I think I'd save nearly 100g with a middleburn duo and lightweight BB over an XTR triple, by my math. . . unless I've missed something?
The change up on my early Duo wasn't nice, though I can't recall the size of chainrings I used.
Not as slick as the tripples, but that was because the front mech struggled to cope.
You can save more than just the weight of the chainring you remove if you're bieng a proper weight weenie:
1) You can shorten the chain by a few links as you're running a smaller biggest ring (12 links if you go straight from 44T to a 32T), typically 8links if you go from 44T to a 36T
2) You can run a medium or short cage rear mech, rather than a long cage (admittedly a very small saving)
3) you can run smaller single ring middle ring bolts (again, a very small saving)
4) A proper dual ring front mech is lighter as the cage is smaller to accommodate a smaller difference in chainring sizes between small and large (once again a very small saving)
Whilst these are small changes individually, the sum of all 4 will be a reasonable weight saving if you're a proper weight weenie, however I am sure many people here will consider it a waste of effort. My opinion: sum lots of these little weight savings together where how you use your bike isn't affected and you'll end up with a significantly lighter bike that will make your riding, under almost all conditions, less hard work. But that's just my opinion.
Took you a while to think of that Rob!
Whilst I agree that there are several marginal gains here, I'd say that changing the bolts in your mechs to alu will save more than going for a medium cage rear and double specific front mech, and cost you £5! Chuck in some pimpy Mt Zoom jockey wheels and you'll save far more!
If you need new mechs go nuts, or replace when they wear out but I'd not bother making those changes purely to save weight, it really will be grammes.