This thread is still very helpfull as I am looking to keep the same size in the front but want a19x10.5 in the rear. Reason is I went with a wider tire in the rear 275/30/19 for more traction off the gate at the track but started experiencing some tire roll on the rim when taking wide curves at highway speeds. If I increase the width from 9" to 10.5" this should stretch the tire in a similar manner as the stock set-up. Does this sound right or will I run into other issues? Thanks in advanced. Also what does the 66.5 signify?