Unfortunately, the original tire size, 27x9.50x15, is now obsolete. No one carries anything in that size any more.
You can find 8.50 and 10.50 wide tires in turf tread but they're pretty pricey. I don't believe I've seen any ags in either of those sizes.
American Farmer makes or made a 6.50-15 traction implement tire which would work good. Another MTD guy said there are 5.5" wide 15" bailer rims with the same bolt pattern as the 990. Need to check those out.
I have 3 pair of NOS 27x9.50-15 Carlisles Turfs, I might sell a pair.
Edited by AverageJoe, September 18, 2012 - 06:45 PM.