Well mud terrains are all fine and dandy, but they wont last as long,
I had Cooper Discoverer ATR's, stock size non the less, last year and i did just fine, you have to just weigh down the back with, oh 200-250 lbs.
But the only problem is i havent seen the ATR's on there web site, so im not sure if there still available. Theyve been replaced with the AT3 on the website, but you may be able to get them still from a tire shop.

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2001 Mazda B-3000 CabPlus "FX2 Off Road"| 3.0 | 5 SPD | 3 In Spindle Lift | Belltech Shackles | UltraGauge |Alpine Head / 10" Kicker Setup | Air Box Mod | Add-A-Leaf| Thrush Welded B4 Rear Wheel | Kobalt Box | Cobra 19 DX IV | Custom PA Speaker | Front/Rear Tow Receiver | 2X Aux Lights | Hideaway Strobes | Back Rack Safety Rack | Amber LED Strobes | Blue LED Strobes | 265/75/R16 General Grabber AT2's