Our solution is to use truck recaps or even just bald truck tires for the pivot tires. They make a narrower track.

Then in the winter, when the ground is hard(er), we fill the tracks with some 0.25" and smaller gravel, smooth it off. After doing this for two years, the tracks are pretty well done forever as long as you don't take tillage equipment across a tire track. The rule here is to never, ever rip or plow a pivot tire track.

Now, the old pivot tires, with the fatter tire sizes, like 16.9's -- woof, are those a pain in the rump to cross. We always take the equipment across the tracks at a 30 to 45 degree angle. They take lots of gravel to fill and in clay soil, the ruts rims are just as big a pain as the rut itself.

Some guys here use boombacks, but they're a mixed bag. Ultimately, if you want smooth fields, ya gotta fill 'em.