might be too late but the method amin2001 isn't the best.
make the text, extrude, then apply a bend modifier. in the bend parrameters figure out the correct axys you need and enter a value of 360. also after you do this, move the text( circle form now) to here you want it on the tyre, and move down his pivot to the center of the tyre. this should do the trick much easer. or, better yet, find a cool texture of a tyre and apply a uvw modifier to the side planes of your mesh and then apply the texture.
here's a free very high rez texture:
http://www.sektor-41.com/forum/showthread.php?t=73
you might need to register first.