nod, I did some checking. I think the largest factory duals are 20.8-42's. However, Wold Wheel and Rim has sold several sets of 710x70-38 duals on the big JD's without any problems. They use a really heavy rim design with two bolt patterns. I guess most of these have gone to Southern Ohio. They are located in North Central Iowa and can be reached at 1-800-443-9653, ask for Ivan, or you can e-mail at ivan@woldinc.com. They sell custom made rims, axle extensions, tires, everything you need.