The tire will be slick at first, take it easy for a 100 miles or so until you get it scrubbed in. The powers are pretty sticky off the rack though so I don't think it will be a big deal. There isn't a break in period for chains/sprockets that I know of. I would just take it easy initially to get used to the different gearing (I don't know how much you changed it)and make sure it was installed properly. The chain will stretch though after awhile. I was told to adjust mine after like 100 miles, but it took about 1000 miles to really notice a difference. There should be a little slack in the chain (check your manual), and I hear a chain that is too loose is better than a chain that is too tight, so you might want to keep that in mind. Are you doing the work yourself? What chain/sprocket you going with? Good Luck.