I want to put 18x10 wheels on my jeep wrangler sport and was wondering what size tires i could use without a lift kit

You can fit a 33" tire (285/65R18, 33x12.5R18, or 295/65R18) with no lift. It's possible to fit a 35" tire (35x12.5R18 or 315/75R18), but you won't be able to off-road because there will be no room for articulation, unless you get flat fenders. If you get 35" tires, you will need to trim the pinch weld at the front of the rear wheel well to prevent it from cutting your tires when you hit a bump. You may need to remove the plastic front air dam and possibly trim the front bumper, or go with a stubby aftermarket front bumper, to prevent the tires from rubbing when making tight turns. If you remove the front air dam, it may cause the hood to flutter when on the highway, unless you get stiffer hood latches, such as the ones from Daystar.