You can go to the John Deere website and navigate to this particular tractor in the agricultural section and select build your own. The various tire sizes are covered there. In my opinion, I like to go with the largest size and width tire possible for better traction, floatation, and load bearing capacity.
In that case, usually the owners manual covers the various tire size combinations in the back. Since this tractor is so old (manufactured from 1966 to 1972); it may be difficult to obtain this info. if it is not covered in the owner's manual. You may want to try emailing John Deere directly from their website and ask for this info. They take a little while to reply but have always been very helpful when I emailed them.
They were available with different sizes.Most popular were rear 18-4-38 not sure about the front I remember most had an odd tall tire that was narrow for that time.We had a 5020 about a 67 was sort of a dud was under powered Deere came out with a update kit to make them have more power like they were suppose to have to start with.
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