Hi there,
I need to buy a new chainset and want to 2 * 9 this year.
What choices are there off the peg? SRAM XX is a little too steep.
How do you adapt a normal 3 ring XT chainset to run 26/40?
Is it worth buying a bottom bracket and getting Middleburn cranks or similar?
What have people on here done and what ratios are you running?
Thanks
Get Specialites TA Chinook chain rings and short chainring bolts from SJS cycles , should be around £70 for the lot and bolt it to your existing XT cranks.
Make sure you buy a 40T middle chainring and mount it behind the spider with the short chainring bolts otherwise you chain line will be all to cock.
I have started using a similar set up and was using a 11-32 cassette, whilst 40/32 was fine on short dry technical climbs (Where shifting to the small ring would be more hassle than it is worth) it became more of a chore when it was wet so I have changed to a 11-34 which actually feels a lot better across all the gears.
I'm running 42/30 with a 34 outback. I went for Extralite cranks which allow a double using the outside of the spider and a special 104BCD 30T ring.
The most cost effective option would be as Kingtut suggested. 104 BCD - 40 ring fitted in the middle position and a 64 BCD - 26 ring fitted in the granny position. I know plenty of people who run this or similar set up and really like it.
Thanks, so basically I remove the middle and outer rings and then mount the new outer ring on the inside of the outer spider and use shorter bolts. Leaving me with a granny ring and an outer ring which is closer to being where the middle was.
Arhh, just read James's reply, thanks. cleared that up then.
Lose the idea of the 40T being the new outer ring, it will always be a middle ring as that is it's true position, and make sure its a middle ring you buy!
What are you riding? 36 -11 is high top end enough for DH race bikes.
why not go 22/36 rings and if you don't need a really low bottom end, use a road cassette, it'd all be quite a bit lighter.
24/36 and 11-34 for me - all the gears I need. I don't see the point in a bigger middle (outer) ring unless you're racing somewhere that has really fast (30mph+) sections that you're pedalling lots on or you're a real gear masher.
Interesting, I was going on the XX ratios. I race a fair bit but hardly ever use the outer but feel I spin too much in the middle. Lazy shifting perhaps, but I feel two rings would be perfect.
As you say 22/36 might be more suitable.
104 BCD - 40 ring fitted in the middle position and a 64 BCD - 26 ring fitted in the granny position.
this also allows you to add a bash in the outer position if you want, tidying the whole thing up nicely (although perhaps chucking away the weight saving that you've made). Take care though, fitting a 40T in the middle position may give you chainstay clearance issues. Depends on your frame.
24/36 and 11-34 for me - all the gears I need. I don't see the point in a bigger middle (outer) ring unless you're racing
I find 40T great for Bristol, it's great on the flatish terrain, and I always have the 26T for steep climbs elsewhere.
Take care though, fitting a 40T in the middle position may give you chainstay clearance issues. Depends on your frame.
I haven't heard of this being an issue, even for people fitting a 42T in that position.
But the 40 just means that you're always on a slightly bigger sprocket than with a 36 - since a 36 gives all the range, why bother with a 40?
The clearance issue is real but is only really likely to affect non-external BB users since they tend to allow for narrower chainlines.
Because I like it.
Fair enough. You never were one to do things that make sense 
a BBG superlight 32T Bashguard is around 26g and is just large enough to keep your chain on but not big enough to take a hit.. but if you are grounding a 36T ring on anything other than a really low DH bike you need to sort out your riding. been using that set-up for a few years now on my main bike.
38/28... lots of undulating stuff locally, so enough to get up most anything I'm likely to ride.
That said If I was running a 36/34 I wouldn't need to run a granny ring as well.
Also with a 36/34 I reckon there is every chance you would spin out or at least be spinning like crazy on something like the HONC with it's long flat sections of road, last year I was regularly in the 44T.
Swedish Chef - you haven't really said what sort of riding you intend on doing. IMO - you want a 40T at least for XC racing in the UK. A 34 at the back gives you a good spread of 9 usuable gears (without having to shift down up front) and means that you are generally in the big ring for 90-100% of the race.
my evil only *just* gets a 36T in the middle with an external BB, it wouldn't take a 40 I'm pretty confident. ofc as I said, only some frames (usually where chainline clearance has been sacrificed for mud clearance) would be a problem, but worth being aware of an pretty easy to check
There is also the options of FSAs new 386 cranksets. 3 bolts fastening 2 rings. But you are stuck with propriety rings. 40/27 sounds like a nice ratio.
Middleburn also do a duo chainset and I think you can now get a 27 ring. You won't be able to go 26 with these as it's too small.
Do these dedicated chainsets not give a better chainline than converting a triple?
No idea what HONC means but if you can spin out 36-11 on an MTB on long flat sections of road go and poach chris hoys job. 
Do these dedicated chainsets not give a better chainline than converting a triple?
Its about the same. Though the chainline benefits of moving to middle and granny are pretty decent. What you wont get from converting a triple to a double is a narrower Q-factor.
Also with a 36/34 I reckon there is every chance you would spin out or at least be spinning like crazy on something like the HONC with it's long flat sections of road, last year I was regularly in the 44T.
Absolutely but that's why I keep my mtb for mtbing and my cross bike for HONC type stuff 
Absolutely but that's why I keep my mtb for mtbing and my cross bike for HONC type stuf
Yer get him and his lahdee dah cross bike.
36 x 11 with a 26" wheel shod with a 2.1 tyre = 25.3mph. Hardly fast - particularly on a road downhill.
+1 for 24/36/bash and 11/34 at the back. You only miss the top two ratios and by the time you're going that speed it's just as effective to tuck in rather than pedal.
I went for a Shimano SLX chainset. 24/36/bash, cranks and BB all in for £99
James P - how do you get that random figure?
you can easily spin 11/36 to 30mph and oncde there on a road descent you'd be alot better tucking in than pedalling like **** all the way down to the next climb
Another +1 for 24/36/bash and 11/34 (although this is on my toy bike rather than an XC mile muncher)
the alternate to flying down a road at high speed is find a trail that will take you down the hill!
I run 24/36 with an 11/32 block and am never short of gears - cept when it gets near vertical.. and then it is my legs that run out not the gears
Whatever chainring setup you're using, for off-road or luggage carrying work, I highly recommend Chris Bell's Oval EggRings:
http://www.highpath.net/cycles/ovals01.html
These are correctly oriented oval chainrings - BioPace was all wrong - individually made to your specification. My bottom line is: they work very well indeed to smooth out your power stroke and eliminate the dead spots at the top and bottom of your pedal stroke. I will be running my 40% oval 24-tooth and 30% oval 36-tooth on my next 2x9 set-up.
More discussion here:
http://www.retrobike.co.uk/forum/viewtopic.php?t=47932&highlight=eggring
Dr. Matt...
Do you need to change from a long cage rear mech to a short cage when moving from the triple setup to double? An LBS kindly replaced my chain last year and made it too short, so havent been able to use my full range of gears or big ring for a year and havent missed it. May need to do as above to give me a slightly longer top gear and remove the dead weight of the big ring Im not using!
Do you need to change from a long cage rear mech to a short cage when moving from the triple setup to double?
No, just a couple of links out of the chain
22/36 here with an 11/34 cassette. You miss the top two gears compared with a 44 chainring and it can be pedalled up to high 20s mph without difficulty. Thats fast enough for me offroad I'll just accept the rare occasions I spin out on road. Its an offroad bike after all. Two chainrings gives better ground clearance and less shifting. 22 ring 1-7 at the back for uphills and 36 ring 1-9 for flat and downhills. Standard shimano chainset
28/40 with an 11-34 on the hardtail, with 28/42 and 11-36 XX on the FS.
I think the 9 speed set up works just as well as the XX! I find I can do the vast majority of my riding in the 40, and just drop to the 28 for steeper stuff.
Works really well, the chain line's pretty good even if you do go big/big.
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