Will a 30 mm cyclocross tire fit a road bike?
 

Or do I need cantilever brakes for that?

depends on the bike (and brake). only one way to find out.

My memory is that traditional caliper brakes only take up to 27mm, but some of the cx tires advertised as very wide sure look thin. My guess is you will need the canti, though.

Yep, try and find out. Then there's some tires that are alot wider than advertised. :lol: :(

maybe

It will fit the rim, but it may rub against the fork blades or chain stays or as others have said, the brakes.

The size of a tire says very little about the how really wide and tall a tire is.
Also keep in mind that when you ride you will get some deflection in the rims side to side and if it is muddy you will get rub from the tire to the frame.
You might want to check with an expert before doing it.
Good luck

I have a pair of Nashbar long-reach calipers that handle 32C tires from a couple different makers.

I tried to fit some 700x32 ritchey speedmax tires on a Trek 1000 road bike. I had to deflate the tires to fit them through the brakes. I ended up having clearance on the sides but the tires were too tall.