All seems to make perfect sense to me, now what I would like to know is, can it be done on on a budget nicking a 10 spd road cassette for an mtb? Is it possible or are the gear ratios too silly etc etc?

Yes – though unless you only ride in Thetford you'll likely want a wide ratio cassette, and whilst they're less than XX the only option I know if is IRD, which aren't exactly cheap That still won't give you as wide range as XX, but it should be useable with a wide range double.

what are you going to use as a cheap rear mech to go with the bodged cassette? 9spd mech wont work with a 10 spd cassette will it. What are you going to do for 10spd shifter? Is the xx chain the same width as a 9spd or is it narrower? may not be all tha easy to get working

Yes, it's more than possible, but will still cost a bit…10-spd mech – easy, a road mech will do that…you just go for the mech that will allow you to run the largest range, road cassettes have a good range available in 10-spd, I think (but can't be certain), Ultegra has a wide range 10-spd cassette.

Shimano also do a road/touring-type set of underbar shifters that are also 10-spd so they can be had. You then just need the chainset and a chain.

Steve Worland of What MTB did a report on his DIY 10-spd set-up when SRAM's XX was being rumoured about – I think a 10-spd conversion costs about £380 if you do it DIY.

I've had a very quick nosey round Bikeradar but I can't find the article, but it was in the magazine about 10 months ago. I think it was the December edition as I posted up on Bikeradar with a few questions about it – Here

9spd mech wont work with a 10 spd cassette will it.

Yes it will. Geometry is the same. A 10-speed chain will run on the jockey wheels. Meanwhile a road mech won't normally work with a 32 sprocket if you do want a wide ratio cassette (they're specced for max 27, but will go to 30 on many frames).

I think (but can't be certain), Ultegra has a wide range 10-spd cassette.

Depends whether you call 12-27 wide range. As I suggested above, that might work if you're riding somewhere flat or using a triple, but if you want a double you really need wider range than that.

You actually only need flat bar road shifters, cassette, chain assuming you already have a 9-speed drivetrain. Using that IRD cassette I make that £260 – could be done for £160 with a normal roadie cassette. Of course that's plus whatever you want to spend on a chainset if you want to convert to double.

I understand the logic for racers. Never in the granny ring, so don't need to carry it, and they probably have the leg power for a closer ratio rear cassette as well, so far all good. Struggling to see the benefits for "regular" riders though. Proper advantages any-one?

More usable gears ratios? How often do you use all 27 gears? I'm betting a fair amount will only use (as an example) 4 largest rear sprockets to granny; most of the rear cassette with middle and smallest 4 or 5 with largest – a 10*2 will give the same range of gearing but without the mad chain stretching ratios that some people ride, i.e. middle ring and smallest rear is about the same as big ring and 4th smallest cog – you have 2 very similar gears on the bike…get rid of the duplicates and leave just the workable ones.

Potentially a lighter system? This forum is loaded with people building light bikes and fretting about weight, so this could be a good opportunity to build a light bike that works (not that existing solutions don't work, but this opens up more possibilities)

Marketing – and it needs something new to allow the companies to sell stuff – a lot of bikers are label-mad, so if a company brings out something new, then a lot of people just jump to it right away as they need the next best thing – it probably isn't going to improve regular riders rides but to them it will – which is important as they are parting with the cash.

I'm interested in it but not at those costs…I'm not convinced I'd do it justice (mainly due to my riding being once-a-week in the eveing if I'm lucky).

I did exactly this thread shortly after XX was announced:

http://www.singletrackworld.com/forum/topic/2×10-on-the-cheap-my-musings

It's fairly easy to do actually with flat bar 10 speed, 24/36 chainrings and a modded 10 speed cassette.

For the cassette, it's a bit more of a faff. Though you can buy 11-32 10 speed cassettes (IRD do one), they're really expensive. There aren't currently any cassettes with a 36 out there though I believe that next year, there will be one designed for 29ers though it's only 9 speed.

A much cheaper solution is to buy a 11-28 10 speed road cassette (£40ish), split it, remove one sprocket (the 12) and then add in the top 32 tooth sprocket from a 9 speed mtb cassette (plenty of people have these in good condition on a worn cassette). Job done.

In the end, I've now got 2×9 (24/36 and 11-34) to try it out before spashing out on anything 10 speed.

get rid of the duplicates and leave just the workable ones.

Aye, good point.

I agree, needs to come down in price before I'd consider changing though

Costs for my full 2×10 method:

Shifter £40
Chain £20
Cassette £40
Chainrings £30

Total £130

Which cassette for £40 – when I priced it in December the cheapest 10-spd cassette that I reckoned could be usable (think it was a 27 or 29 largest cog) it was £80…

Without searching again, I think it was a SRAM one and 11-28 as above.

EDIT: quick search finds £47 for a SRAM one:
http://www.chainreactioncycles.com/Models.aspx?ModelID=40237

I'm sure that you'll find it cheaper if you spend time looking.

The problem you'll find with your plan of putting a 9-speed cog on the end of a 10-speed cassette is that the biggest cog needs to be dished (given that the actual cassette on a 10-speed is wider than a 9, whilst the splines are the same width). If you try to space it correctly the smallest cog will be too far out and you won't be able to screw the lockring on.

See diagram from Marchisio

Unfortunately Marchisio only make cogs up to 30, so if you want 32, your only choice really is IRD.

Hmm.. admittedly I didn't factor that in… so that is an issue then…

I'll bet there's a way round it – just haven't worked it out yet 🙂

Anyway, as I said, for now, I'm happy trying out 2×9 to see if I like it

More usable gears ratios? How often do you use all 27 gears?

Potentially a lighter system?

I agree, needs to come down in price before I'd consider changing though

guys, guys there's a much simpler solution, show 'em Sheldon

Then again, have you actually tried it? From sheldon brown, I calculate a 9 speed cassette as 36.5mm wide with a 10 speed one at 37.15 – eg 0.6mm difference. Not sure that that's enough to cause a problem assuming you're using the right spacers, etc..

http://www.sheldonbrown.com/cribsheet-spacing.html

9 speed shimano = 9×1.78 + 8×2.56
10 speed shimano = 10×1.6 + 9×2.35

I guess you'd also be adding in .18mm for the wide 9 speed sprocket that you're bodging on tough so it'd be a total of 0.78mm wider.

Ah, maybe all too much then when added in to the inherent 0.65 difference in width from 9 to 10 (which I guess is accounted for normally by the dish on the 10th one)

If 10 speed cassettes are wider, why do you need a spacer behind 10 speed ones on 9 speed hubs? Are the sprockets offset then?

Are the sprockets offset then?

Yep – pretty much as shown in that diagram, only a bit more (I don't think Marchisio use the extra spacer behind the cassette for theirs).

At first glance that diagram looked rather confusing, but I see now. Alright then, why?

It's to do with 10-speed specific cassette bodys (you don't use the spacer on one of those as they're shorter). Not quite sure why they made the body shorter.

That's a diagram for Marchisio sprockets compatible with 10-speed only bodies – the previous diagram is for the older sprockets which won't work on those (hence no extra spacer). I should give a link to where I'm getting these from http://clemenzo.com/index.php/content/view/12/31/lang,en/

Forced incompatibility?!

If you adjust the high and low adjuster screws on a 9sp rear mech to their max, would they cover a 10sp cassette ?

I'm not sure I see the point in bodging a 2 x 10 drivetrain with a 10sp 11-32t cassette. You might as well bodge your existing 9 speed triple chainring set up into a double, as clubber as done, as it will still have the same range of gear ratios, but would be cheaper than bodging a 10spd. The only advantage of using a 10sp 11-32t cassette is that it offers closer ratios – is that enough to offset the cost of having to buy 10spd shifters, mechs etc. for the typical MTBer?

If you adjust the high and low adjuster screws on a 9sp rear mech to their max, would they cover a 10sp cassette ?

Yep.

Agree with Sum, unless you're going to use the 11-36 cassette there's not really any point in 10 speed!

I run 28/40 with an 11-34 cassette, it seems more than adequate!