On JD sidehills, the tires are vertical, but on the Hillco conversions, the tires are perpendicular to the ground as the whole axle tilts. The diamond tread tires get better grip on extremely steep and soft ground.
Here in oregofornia the combine harvest weather is hot and dry. The only harvest that needs bar lugs is corn and late beans. Sometimes cauliflower and broccoli have a damp soil harvest too. But the combines roll from late june in crimson clover to late september in red clover. Rains dont usually start around here in any quantity till october.
Lots of valley grass machines run the skirt on the rear for wind/air reasons. Grass harvest with a tail wind dont go over too well.
Notice the loader tractor with floaters? Planter tractor.