I have a Specialized Allez Sprint that I use for crit racing. I’m really interested in trying cyclocross this fall but can’t buy a new bike right now. Has anyone ever raced cyclocross on a road bike with cross tires? Do you think there would be any reason to not try it on the bike I own?
Your typical cx tire (a 33c) won’t fit in most road bikes. There may be a few exceptions. Some of the more endurance oriented road bikes with disc brakes have increased their tire clearances in recent years. You could also find a cx tire narrower than a 33c, but I wouldn’t recommend that for a new cx racer. For someone in their first year, I’d recommend running a little fatter tire to help handling and comfort. I’m like 99% sure your won’t have enough tire clearance on an allez sprint, even if your run a narrower tire. The rim brake version is probably only cleared to a 25c, and disc version is probably only rated to a 28c since that frame is really oriented for road/crit racing.
My opinion, don’t try it. If you scan eBay and other local used sites, you should be able to find some good deals on older cx bikes, especially if discs aren’t a must have for you
I can fit 32mm slicks in my Defy, but 30mm CX tyres rubbed. I ended up getting a cheap 2nd gravel bike to try it out, firstly on the 30mm CX tyres, but got 38’s over the weekend - they made a massive difference.
I guess it depends what you want to try at cyclo-cross. Early season races here in the east of the UK are typically very dry and you could probably get away with 28mm tyres. If you want to play in the mud then I would go for buying an eBay special. Even if you can get the tyres on, do you really want to possibly trash bearings, derailleur etc just to try it out?
I would agree with @steveking that it depends on what you want to try and where you are. I did my first few cyclocross races on a track bike with 23mm slicks because it was the only bike I owned at the time. I didn’t do well at all, but I did have a very good time. If you have some dry, fast races near you I’d say throw some Panaracer Paselas (or something) on there, let out a bunch of air, and give it a rip. You probably won’t do well and you’ll be racing your bike more than your course or the competitors, but sometimes that’s fun. And if it gets you out to a race, that’s even better. The community is really what makes cyclocross (in the US, anyway) special. My only caution would be that road bikes and road bike parts are not meant to take the abuse that cyclocross dishes out. The Allez Sprint is tough, but the hanger, wheels, and derailleur not so much. But hey, it can be done!
If you’re just looking to dip your toe in, it might also be worth asking around in your local community to see if anyone would lend you a bike for a race. We do that a lot here - it gets people hooked.
TL;DR Ride your bike, have fun, drink a beer afterward
In general the CX community is pretty welcoming and if you’ve been racing crits I’m sure there’s some overlap and you have some buddies who race CX. Tell someone you want to give it a shot and see if you can’t find a bike to race on for a week or two