Here's a link to tires, with a good, bad, and ugly comparisons.
Google Image Result for http://carverequipment.com/images/R3-R1-R4%20tires.jpg
I had (on the tractor I just sold)a tire called Field and Turf. They were a turf style tire with huge gaps between the nobbies. They worked great in snow, on the lawn and even in the wet pasture. When I got into 'soup" they clogged up but would unload when I picked up speed. I'm getting R4's on m new Kubota 5740. Kubota no longer offers the field and turf tires! I even thought about swapping them out because after ten+ years they were still in great shape.