Section width is not the same as tread widthHow does that work? 225/50/xx and 225/55/xx have the same tread width. In either case the tread width is 225mm or 8.9”. The 50 and 55 indicate the sidewall height as a percentage of the tread width. One would be 50% and the other 55% of the tread width. So, 4.4” and 4.9” side wall height respectively.