Triple R et al, The rear tires are Kubota OEM R1 14.9 x 26 The fronts are 11 R 16 Michelin XM27 Utility & Industrial. They have a R4 carcass and an R1 tread. They are only .5 inches larger in diameter and 1 inch greater in rolling circumference than the Kubota OEM 9.5 x 16 R1's. The front wheels are Kubota OEM R1 16 inch wheels. I chose this after much research, and particularly after not enjoying the "water-bed" look of regular R1's with a heavy FEL load. I wanted R1 traction and R4 stability for my duties, and these provide both. I operate them at max psi since I never drive fast. The ride is (to me) the typical R1 feel, the bars are never as smooth as an R4 tread. All of my duties are on soil or at most gravel/dirt road, so the ride quality is not an issue for me. Here is a data sheet on them.
http://www.tractorbynet.com/forums/attachment.php?attachmentid=300773