I am speccing out a custom steel frame (I will probably go with Doug Curtiss at Curtlo who seems to offer a pretty combination of reasonable price and good service) and I need to decide on a couple of options. Cyclocross bikes are thin on the ground in South Africa, so I am trying to figure this out as I go along.

I'll be using the bike mostly for fire road riding, a bit of singletrack, and some commuting. A bit of interest in cross racing is developing, and I'll do a bit of that in a low key way when it gets off the ground. Summers here in Cape Town are dry, winters are damp, but not pacific northwest damp. Surfaces tend to be firm, and the terrain is pretty hilly (I'll use the bike fairly often on a route that climbs 900m in 10 kilometers).

1. Rear spacing/brakes: I run Campy on my Road bike, and it would make sense to be able to swap wheels and cassettes easily, which would mean chosing 130mm spacing and cantis. On the other hand, disc brakes and mountain bike hubs make a certain amount of sense for the riding I'll be doing, and I am hardly going to put delicate record clusters and Ksyriums on the cross bike. Discs have transformed my mountain biking, and I imagine they'll make long offroad descents on a twitchy cross bike a bit easier.
So maybe I should go with 135mm, and DT swiss disc hubs (which can take campy cassettes) and leave it at that? I'll probably put cantis on initially anyway for budget and weight reasons.
Or should I keep it lean and elegant - 130mm spacing, no disc tabs?

2. Either way, should I forget trying to stay with Campy and run SRAM or Ultegra?

3. Can anyone recommend a good, but not too expensive carbon cross fork with disc tabs, or without if you think I should go the purist route?

4. As I mentioned there are some big hills around here, so was thinking of running 34/50 up front. Any reason not to?

Anything else I should keep in mind?

Thanks in advance.

Yeah, go with Campagnolo :D The only 130mm disc hubs I can think of are Phil Wood, and they're Shimano only. If you go with a 135mm frame, there should be more options for a disc-brake-equipped Campy hub.

I don't know of any carbon CX forks with disc tabs, but there are lots of 29'er forks that will work as long as your frame geometry compensates for the extra height of a "suspension corrected" rigid 29'er MTB fork. Maybe Sibex or Pace make a CX fork with disc tabs...

1. the brake system is definitely your call. i'm a bit of a purist and run canti's myself, even though my 'cross bike is disc ready. though they can be tough to set up just right, canti's are light and the swapability between your road bike could come in handy...

also, some people have been having great success with those mini v brakes. a friend just built up a bike with them and loves them. great stopping power, easy setup, and no chatter issues (though his soma fork is BEEFY!)

there are also race legality issues with disc brakes. those 240 hubs are sweet though. you could setup the frame for both and space it at 132.5 so you just have to squeeze the stays one way or another depending which setup you're using. my bike came with velomax sagitta wheels, which have 130 spaced disc hubs. i don't know if they make them campy compatible.

2. if you like campy, run campy.

3. winwood makes a nice disc specific 'cross fork... there are lots of nice non-disc carbon forks out there. i run a ritchey wcs. i really like it; it seemed like the best bang for my buck.

i'm not familar with curtlo frames. have a link? eventually i'd like to get a custom steel desalvo 'cross frame.

You could always go with 132.5mm spacing so you can use either 130mm or 135mm hubs.

Thanks for all this. I'm a bit torn on the disc issue. I found them such a revalation on the mountain bike that I'd like to keep the option open, but the lighter weight and general stylishness of cantis also appeals. I'll probable get Doug to braze on a disc mount, and build the bike with cantis. He's at www.curtlo.com, and will build frame (true temper platinum) for $755 - a guy I occassionally ride with has two of his road frames (one in the lighter s3 tubeset) and they seem pretty well put together. I can't justify a steelman/indy fab type of price tag with my modest ambitions - too much sunk into road and mountain bike bling already ...
I asked him about the 132.5mm option, and while he says he'll do it he reckons it puts a lot of stress on the axle because the alignment is imperfect - not that that seems to bother Surly owners.
But campy it is, and canti's for now, so that's two dilemmas solved.

nashbar offers a carbon cyclocross fork that is disc ready. on sale right now with an additional 20% off.
I bought one a while ago, but still haven't gotten around to building up the bike.

cheers
Tony O