It is clear he was asking about tire width and of course the answer to the original question as stated is no. However the discussion has morphed into one about modifying road frames to fit larger tires?? In which case I would like to throw in my 2 cents, which may be less than yours because I am Canadian. haha I just dissed myself... rough.. anyway I have seen plenty 27" vintage frames (like my friends beautiful raleigh super grand prix, tange 5 tubing) that have nice long reach calipers that have just enough adjustment left that you cold throw on a 700c and some fat ol' tires. Even with the 27" there is lots of clearance and I suspect it is for older more bulky fenders. That being said your braking power would suck and you definately don't want that for mountain biking and there is the inevitable problem of mud and crap getting caught up in caliper style brakes. you can get posts put onto your road bike. The shop here will do it for 200 bucks (ouch!)... but if you are only doing occasional off road with no steep decents than maybe calipers will be okay. But then again I would just get a 29" MTB or surley if that is what you really want. These money saving build projects can end up costing more if you factor in your time etc...