There simply is not a proper current tire that goes on the rear due to changes in tires and rims requirements over the years. As the other poster said the original tire size was 13.50-28 which ROUGHLY translates somewhere between a 14.9 and 16.9 tire of today. But there is a huge difference, the original 13.50 tire was designed to go on a 8" wide rims todays 16.9 is designed to go on a much wider rim thus they are crowned up when mounted. If you want the tractor to look right Your choices are to find a good set of 13.50 tires which isnt likely or to widen the rims so you can use either 16.9 -28 or larger. The later As came out on 14.50-28s which equals todays 18.4-28. The picture included is my A on the later 14.50-28 size rears.