I have been taking part in a few adventure races where at least 80% of the cycle has been on the road, and the other 20% on off road. I don't have the money to buy a cross bike. Is it possible to convert the road bike to a cross bike? Perhaps by putting cross forks on? I basically want to be able to tackle the off road bits at a decent speed without having to worry about punctures or wheels going from under me.
what's the biggest tire you can put on the back? A cross fork will almost surely be longer than the stock fork on that bike, so the steering will be funny. If you are doing actual cross racing, the organizers like to provide muddy stretches, so clearance is a big issue
Have you looked in the cross forum here? I have not, so I have no idea if they could help you.
This definitely belongs in the CX forum, but the general consensus will be that you can race CX on any bike if you don't expect to win. A CX fork will help, but you still don't have proper clearance in the rear so if there's mud you could be in trouble.