275/70 or 285/65
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Depends on the engine and the axle ratio. I have the 20" wheels with 275/55/20 Vogue tires. I lost no power as that is the factory correct size with the 3.73 axle and the 3.7 V6. If you have the 3.15 axle, I would be looking for a wider but shorter tire, regardless of engine, to pick up the power. The diameter of the tire is everything when buying new tires. Don't shoot yerself in the foot and buy tall tires unless you have the engine and gears to pull them.