What's the biggest tire that can fit on stock rim?

[VxSport]

We are running a discontinued Dunlop tire, Maxx Traction Mud terrian, 275/65 R18 on stock rims. Now the crazy thing is these wheels and tires were from my Amigo project. These tires (set of 5) now have about 50K on them. I took it in for balancing two weeks ago, average tread depth 15/32 (New 17 or 18/32").
Now the only clue I have to why they are doing so well. These tires are 90psi (9 ply sidewall) tires designed for Heavy Duty Dullies.

[pbkid]

We are running a discontinued Dunlop tire, Maxx Traction Mud terrian, 275/65 R18 on stock rims. Now the crazy thing is these wheels and tires were from my Amigo project. These tires (set of 5) now have about 50K on them. I took it in for balancing two weeks ago, average tread depth 15/32 (New 17 or 18/32").
Now the only clue I have to why they are doing so well. These tires are 90psi (9 ply sidewall) tires designed for Heavy Duty Dullies.

I run terra grapplers which are 60psi tires and i run mine at 60 psi, ive already gotten around 50k miles on them and they still have loads of tread left...