How's the side wall comparison ? And the roundness ?
The 37x13.50 Cooper STT Pros come in a Range E sidewall and so they are much thicker and tougher like a 37x13.50 Toyo MT would be. 37x12.50 Nitto Trail Grapplers are only Range C and that's why you see so many of them have sidewall failures. As far as roundness goes, it's hard to say for sure just yet being that the only set we've run are the ones on our Renegade and they were mounted onto steel wheels. Granted, they balanced fine but what I really want to know is how these new 37x13.50's will feel after mounting them up on our ATX Chamber Pro II's. It's be great if they just felt balanced like our Toyos do but, I'd be just as happy if they can just be balanced on a machine.
What I do like most about the Coopers STT Pro is that they're about $350 a tire where as a Nitto Trail Grappler is about $400. See links below:
https://www.amazon.com/s/ref=nb_sb_...37x13.50x17&sprefix=cooper+stt+pro+37,aps,213
http://www.amazon.com/gp/product/B0...37x12.50x17&qid=1456782952&ref_=sr_1_1&sr=8-1
Over 5 tires, that $250 and almost the cost of another tire.