Farm wagons don't have springs. So this will be no problem at all. If you want to improve on your design and haul more there is away...

Your tractor has a bucket so you have hydraulics. on a non steering axle you can ad a hydraulic brake. a single cylinder that would break a shaped smooth section of steel to the tire tread area to produce friction that will slow the rotation of the tire. If you have a lever that has a float position this would be best as you can push the lever to increase friction and if the tire would lockup you could easily push to float to quickly release the hydraulic pressure and then back to center and add a little resistance again to slow again.

I was going to do this to a wagon that I hauled round bales with but stopped renting the farm and no longer had the steep mile long descent from 50 acres of hay fields.

Good Luck!

Ben