There is no flywheel effect.. if you were to spin a tractor tire fast enough for it to generate enough centrifugal force to distribute itself to the outside of the tire it would evenly distribute itself and begin to spin with the tire. But since tractor tires turn so slowly the water just 'slips' inside the tire and basically is just a U shape of water inside the tire moving with the tractor but not really 'spinning'.
You do still feel it as 'normal' non-spinning weight, mostly during starting and stopping. My theory is that the smaller the tractor, the more noticeable it is. Not having owned a big tractor, i can't say for sure.