I'm betting you are not using the proper load chart on the Firestone or Titan sites. A combine is going to be a cyclic loading application. Here are the pagesof the Firestone Farm Tire Date Book which I believe applies.
TABLE F1 Radial Ply Agricultural Drive Wheel Tires Used on Agricultural Harvesting Equipment in Cyclic Loading Field Service and Road Transport (Excluding Hillside Combines TABLE F2 Diagonal (Bias) Ply Agricultural Drive Wheel Tires Used on Agricultural Harvesting Equipment in Cyclic Loading Field Service and Road Transport (Excluding Hillside Combines) |