Yeah I found it odd many tire manufacturers say you need an 8.5" rim for both 12.5" and 13.5" tires. Shouldn't the inch narrower tire fit on a smaller rim?Discount will indeed mount them, unless you come across someone completely incompetent. The goofy thing is that what the tire manufacturers recommend differs greatly. Yokohama lists the minimum width for the 37x12.5r17 Geolander M/T G003 as 7.5 inches. While BF Goodrich lists all tire that are a 285 section width as needing minimum width of 8 inches, except for the 285/70R17 found on the Rubicon, which it miraculously believes that 7.5 will be just fine.
Discount Tire's website list a lot of 12.5" will fit on a 7.5" rim, even if the tire manufacturer says 8.5".