First Cyclocross Race - Riding a Mountain Bike

Many first time cross racers use a mountain bike. It makes perfect sense, don't go out and spend $1500+ before you even know whether cyclocross is your cup of tea. Most all races allow mountain bikes, the only type of equipment that's usually forbidden is a fixed gear.

A full suspension mountain bike will do just fine as an introductory race vehicle. Your primary setback is that it's heavier than a cross bike, so it will slow you down when carrying it up a steep incline, or carrying it over the barriers, etc. But, those beefy ( and heavy ) tires might carry you through the mud quite nicely, maybe even putting you at somewhat of an advantage in a muddy beginners race.

Just be friendly and courteous out on the course, cyclocross is about having fun.

Being a CX race, I expect it to consist of mostly asphalt and dirt roads. In those circumstances air drag plays a huge role (it is proportional to the square of velocity). Thus do learn to lean onto the handlebars. I can't produce a picture right now, so I'll describe it.

Sit firmly. Your ass and legs are supporting you. You hands observe zero push and zero pull force from the handlebars.

Use the outside surface just below the elbow of both arms. Rest it onto the center of the handlebars, much like a TT racer.

Voila! You have a road racing posture on a mountain bike! The rest you will handle with ease.

CX is often about carrying your bicycle as much as your bicycle carrying you. When carrying a bicycle on one's axle, its aero properties do not play any role, I would guess, while its weight does.

CX bikes are actually designed so that they can be carried in a specific efficient manner (pay attention to how the man above holds the handlebar). A larger front triangle without any bosses or cables on the top tube to touch. An MTB frame, especially with full-suspension, may have a very tight front triangle, and will definitely have more weight.

Compare typical front triangles:

versus:

If there will be barriers on your course, you will have to carry your bike (the barriers are usually organized in such a manner that one cannot bunny-hop all of them). Make sure you can lift your bicycle without busting your back, or tangling in it and falling.