New Tires for my F450

Thanks for the reply's everyone. I usually change tire sizes from the factory size to personalize my rides and provide better handling appearence etc. My 450, I was hoping to lower RPM's at highway speeds as they are quite high with the 4:88 gear set. Also the wheel wells are HUGE on this truck and wanted to fill them up somewhat also. I am concerned about safety (I'm a professional firefighter, 32 years service, seen enough accidents to last several life times)so I think I'll just go with the factory size. I don't want to use a wheel spacer as the tires are now just barely inside the wheel wells and i'm too old for the tires to be "hanging out". Been there, done that! I just wish they'd make a tire that is taller in the same width. Not much available in this size i guess. This is my first dually and am still learning about some of these things,some limitations were never a problem with my single wheel trucks. Love this truck though. thanks again. Cheers John.