I have an 07 F150 4x4 ext cab and the wheels I plan on getting are 20” x 8.5offset 30, and backside 6. What is the maximum tire size I can run with out any clearance issues? I see websites show 275/60R20 as an optional tire size, but can I go bigger? I DO NOT want to install a leveling kit because I don’t like the way it looks when I tow my boat. Thanks!

 

I'd go with a 305/55-20 (33x12.50) on those wheels. I know you said you don't want a leveling kit, but if you combined that tire/wheel package with a 2 inch leveling kit and added a small lift block out back, (so your truck won't "bulldog" while towing) it would really look great.