You can ride your mountain bike in any FRS-CX/Florida Cyclocross event, with tires as wide as you like, as long as you don’t have forward facing barends. Fact.
If it is a UCI race, you can not ride a tire wider than 34c, and you must have drop bars (same with a national championship, or national calendar cyclocross race).
Each race promoter decides if he or she wants to include a separate category/class/race for mountain bikes in FLCX. Not one promoter has ever specifically said MTB’s are not allowed that I’m aware of.
There are many CX aficionados who feel that riding MTB’s is against the spirit of CX racing, and they aren’t wrong, but their feelings are just that, their feelings. Those feelings belong to them and do not affect you in the slightest. Even if they say something shitty to you, it’s still them being shitty; those words have no official weight.
With that said, if you have never even tried to race CX on a CX bike, you are cheating yourself of half the fun of CX, the fun of trying to control a skinny tired bike through off camber corners and sharp climbs and descents. Yes, of course it’s easier on a mountain bike. The point is that CX isn’t supposed to be easy. That’s a lot of the fun of it.
No one who is trying the sport of CX for the first time, or indeed even the first season, should feel bad, or allow someone else to make them feel bad, about riding an MTB in a CX race. Bikes are expensive, and spending $1000 or more on a bike to try out CX before you’re certain you’re going to like CX is just plain foolish. So all you beginners out there, don’t take any crap, just run what you brung and have a blast.
If you decide you want to keep racing, then, by all means, I encourage you to borrow a real CX bike and race it a couple of times, and if you decide it’s for you, go down to your local shop and buy a CX bike. They are super-rad, and they’ll make you a better rider on all of your bikes.
If you decide the CX bike scares the dickens out of you, and you just want to keep riding your mountain bike, that’s fine, too. But you shouldn’t feel that any CX promoter is obligated to schedule a specific MTB race- it is a CX race, after all. There are many MTB races on the calender, and I doubt that any of them offer a separate CX bike category. Nor should they, it’s an MTB race.
I hope that once and for all we can move past this topic and move on to more important ones, such as “how can I sucker more of my friends into coming out to race CX” and “who can grow the weirdest beard for CX States”?
That last one is a trick question, y’all. I’ve got that one in the bag.