What tire size do I need to run 34's or 35's on my stock 18" rims?

I already have 1.25" Wheel Spacers, 2.5" TeraFlex Lift and the 1" P.A. Body lift installed.

Thanks

 

Unless you particularly want to keep your stock 18" wheels, you can buy new, 16" wheels and 34-35" tires for about the same price as you'd pay for that size tire on 18" wheels.

For your 18" wheels, 305/70 is about 34.8" diameter. This is a useful calculating tool: http://www.miata.net/garage/tirecalc.html

 

I think a few people here have the 35X12.5R18 BFGoodrich Mud-Terrain T/A KM2 or Nitto Mud Grappler tires. They is only approved for 8-11" or 8.5"-11" wide wheels (stock 18 is 7.5" wide) so you may have trouble finding a tire shop that will install them.

If you want to stay in the approved rim range Toyo and GoodYear make a 285/75R18 (35") but they are Load Rating E so the ride might be rough.