Alan.. I just ordered a pair of 26x12-12 Carlisle Field Trax to install on my 400 tractor. They're for 4 wheelers, gator type machines and garden tractors. They're costing me $94 US. They should provide better traction without digging up the grass.
http://www.blujay.com/?page=ad&adid=2450249&cat=11140000
Army

http://www.blujay.com/?page=ad&adid=2450249&cat=11140000
Army