Probably a very stupid question but here goes…

I want to go on a long ride this Friday night and bivvy in the hills but in order to get there and get enough training miles in I was thinking of taking the road bike. It's steel with carbon forks. If I put cyclo cross tyres (if they fit) on it would I be able to go off road a bit without killing myself and/or the bike?

Depends on the bike…but at a guess the tyres will fit onto the wheels but the brakes probably don't have the clearance required, also if it's a 'proper' road frame (as opposed to a tourer) the frame clearance will not be sufficient either.

You could always try riding off road on slicks and see how you get on?

Depends.

Not if it's close clearance frame or most likely if you have standard drop calipers (the tyres will usually foul them)

A mate uses an old steel road frame as a CX bike, uses the narrowest CX rubber he can find. OK the compact screw-on block, neglible mud clearance and dodgy brakes are a limit compared to dedicated CX kit, but it does the job and he is pretty handy on it.

Most road kit will take a fair bit more abuse than people seem to think. I just wouldn't take anything I'm too precious about offroad.

So, if I manage to find a small enough tyre I should get away with it by the sound of it. By biggest concern was snapping the frame or forks but I won't be doing anything too rough just need to get far enough down a bridle way to find a decent place to sleep for the night! Any tips on where t ofind skinny, skinny cyclocross tyres then?

I don't think you'll break it. You can probably just ride it as it is – Paris Roubaix is often done on regular sized tyres. Just need to avoid square edged hits that might puncture you.

Likely issues:

1. not getting tyres on
2. pinch flats whether you do or not
3. pedalling up anything steep
4. riding down anything technical
.
.
.
1,000,000. breaking the frame

Just ride it as it is. I regularly ride my road bikes (alu and race carbon) off road. They're fine for it.

Depending on clearances, you ought to be able to get a 26 tyre in, and might even be able to get a 28 on there. With that, you can go anywhere.

With that, you can go anywhere.

…although you may be walking, with your bike on your shoulders.

…although you may be walking, with your bike on your shoulders

Nah. Everything's rideable, especially in the drops… 😉

If the clearances are tight, something like a Schwalbe Marathon should fit, and has enough puncture protection/forgivness offroad, I regularly use my road bikes offroad as I can get to the quite roads quicker by going along a few trails.

LOL OMITN!

With the exception of steep and rocky (which the OP doesn't sound like he is planning) you can easily ride more or less anywhere on a regular road bike. You might need to slow down to avoid punctures, but apart from that go for it.

Try the 24C[does fit a road bike] Halo Courier Berlin Puncture Protectiom tyres from billys.co.uk as these are fast on the road yet are designed to go off-road{closed block pattern with Twin Rails to reduce rolling resistance} Also do not forget the Raleigh Puncture Resistant tubes from cyclelife.com

Once upon a time that was all we had. Take a look at what used to be done by the members of RSF before mountainbikes.

Frame should be ok but using road parts off road is likely to break or increased wear.

You could always beef the parts up and upgrade the fork.

Bonti race x lite wheels for the road are also used by CX racers too.

Just put some nice sturdy tyres on with a bit of a tread pattern and don't ride like a loon. It'll be fine.