40" Mud Grapplers for 18" MC2 rims ?

[1GaNole]

Ok, it's time for new shoes. I have a 04 with a 4" Rancho lift and 18" MC2 Billet rims. I looking for a set of Nitto Mud Grapplers 40"... I see 40's for 17" and 20"... am I missing something ?

I would appreciate any and all input.