The tread profile of the tire ISN'T quite right. 

 It's more like a tire that'd be on a front end loader in a gravel pit, then the tractor style that'd normally be on one of these machines. 

 What can I say, my tire guy offered me a great deal on this set of tires, rather then the original style tires. 
unnamed (28) by 
Anthony Kalnoski, on Flickr