I have 275/70 R18 (33.2x10.8) Toyo Open Country All Terrains on mine with stock 18" alloy rims. No rubbing on the skid plate and no lift on my truck.

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2008 Double Cab 5.7 4X4 SR5
MODS:UWS low profile Tool Box, UWS Stainless Step Bars, Toyota Bed Extender, Magnaflow dual/dual Stainless Exhaust, K&N Filter, Alloy Wheels, Toyo Tires
MODS to do: Backup camera, leveling kit, etc. etc. etc.