I recall when i looked up the cost of the wheel spacers on the wholegoods list there was an asteric with the wheel spacers regarding use with the belly mowers. I'd say Chuck is right, and the extra width interferes with the mower wheels. If my memory is correct (and it certainly may not be), i'm thinking its one deck there was a problem with and not the other. I might speculate there is an interference issue with the 60 inch deck but not the 72...... though, i could have that backward. I would expect your dealer could answer your concerns easily.