You might be surprised your grain cart likely has lower lbs/Sq. Ft of pressure on the road surface than your diesel pickup truck.
I hear you but I think the wagon is still worse.
I'll grant you that the wagon has bigger tires and the tire patch is correspondingly bigger. But the wagon is 40000 pounds loaded. The truck is about 6000 pounds and prolly about a quarter of the tire patch at 1/2 the tire pressure.
So the truck has 4x the psi on the driveway for tire patch, that becomes 2x taking tire pressure into account but the weight ratio 6:1 takes that to 1/3. I know it's a swag, but that makes the wagon 3x the psi on the driveway.
Forgetting the numbers, all you really have to do is watch the driveway bend when the wagon rolls on it.