I am in the process of building a winter road/cx bike for my daughter as a durable road bike that stops in the winter.
So far I have disk frame/forks and disks.
I now need the following:
Wheels- can these be standard mtb ones or they need narrower rims for the road tyres?
drivetrain-could I use some of the XT stuff I have lying around as the gears need restricting anyway?
bars-Is there a special CX spec or can I use standard bars?
Thanks for any advice.

Wheels- can these be standard mtb ones or they need narrower rims for the road tyres?
CX disc and 29er wheels seem to be treated as interchangeable, although I’ve no practical experience of this. Might depend how narrow you want to go on tyres too.

drivetrain-could I use some of the XT stuff I have lying around as the gears need restricting anyway?
Yes, although depending whether you are running 9/10/11speed you may have to be careful with STI cable pull ratios (someone will be along in a minute who remembers how this all works better than I do I’m sure)

bars-Is there a special CX spec or can I use standard bars?
No special spec, run what you like/have lying around.

Ebay bargain hunting is good for this!

Wheel wise, check your hub spacing, some frames are 135mm, some are 130mm. Mtb 29er wheelsets are 135. If she wants to run proper road tyres ever, mtb rims maybe too wide, if she’s only ever going to run 32mm and above hybrid/ knobblies they would work ( personally I reckon being able to put a proper set of 25mm road tires on is a good Idea)

Xt cassette will work, the deraileurs probably have different cable pull lengths for sti’s
Mtb cable disc brakes have different cable pulls to road cable disc brakes. If you are using road sti levers you need road calipers

Cranks wise the shimano hollow tech stuff is interchangeable

This was £400 total

http://ink361.com/app/photo/ig-783922454496404493_408448

Charge filter frame and parts bin/ ebay bits

Wheels-wise: 29er mtb will be fine as long as the spacing is right (which most cx frames will be), and the cheaper wheelsets will be 19mm internal rim width, which is fine for 25mm tyres – i’ve done this for many miles. Downside is that they’re pretty heavy, but they’ll be tough. Comparitive ‘cx-specific’ (basically light 29er disc wheels)are still few and far between, and more expensive.

Xt cassette will work, the deraileurs probably have different cable pull lengths for sti’s

9 speed mtb mech for 10 speed cassette and 10 speed road levers

9 speed Shimano Deore MTB rear mech works perfectly with my 9 speed Tiagra STI shifters. I use a road front mech but MTB should be fine too.

Wider rims and narrow tyres don’t work, so if you want to put road tyre on at some point then go with a narrower rim. I had lots of punctures on 28mm tyres on a 19mm rim on towpath type rides. No problem with 35mm tyres on 19mm rims fully laden off road, but they are draggy on road.

Check frame spacing for hub width options, but if its disc specific it should be 135mm for MTB hubs. Some frames are 132.5mm so can accommodate either.

Any old bars will do.

keep an eye out for wheels with mavic rims, generally they are quite behind in the width stakes so 17mm rim should be available.

as others said 9speed rear mech will work with road shifters and cassette. You could use all 9spd XT drivechain with some road STIs, just not sure how the chainline would be, probably useable even if a little out. The big jumps of an MTB cassette and generally low gearing may or may not be what you’re after. xt f mech probably wouldn’t play too nicely with a road chainset.

Not sure on the bars, standard or OS clamp as per road/mtb, cx tend to have compact drops, don’t think I’ve seen CX specific strength bars tho. Any road ones will probably do, just get width/drop to suit the rider.

Cheers everyone.
Hopefully to get started I will be able to use most of the stuff I have!
With reference to the bars how to I whorl out sizes, widths etc?
Will probably look for some road rims on cheap hubs.

I use a road front mech but MTB should be fine too.

Not sure if it’s the case across the board but I (and LBS) couldn’t get an MTB front mech to work with STI. Best to stick with road.

9 speed MTB runs with 10 speed road.
I’d run a mtb cassette (32t ish) with a mtb mech Sti’s and a compact road chainset.
that will give her a huge spread of gears.
wheels if its a disc frame 99.9% sure it will be 135mm, so a mtd rear hub will work.
I’d hunt down a hope XC rear, on a crosser it will last for ever. Open pro, sport, or CX22 rims. =wide enough for a 35 thin enough for a 23.

Bars just some road 400mm or narrower if you can fid them. Try Carbon cycles for bars stems etc.