Ok the Corsa A/C measurement is 467. The Tora is listed at 505. That makes 38 mm or a litlle over an inch and a half which would be closer to 2 degrees change in headtube angle. Now XC probaly won't be the end of the world but I would still try to go with a normal tapered HS and a reducer if you can find one. bigger tire on the front wont change the A/C but will still raise the headtube and slack the angle a bit.