205 it the width in millimiters, and 75 means the height of the tire from the rim is 75% of its width. THis calculation is valid when you compare same model tire of different sizes.
HOwever, there can be real differences between manufacturers. My son has 205 75 Michelin tires that are smaller in diameter than 205 70 of another american made tire...
4x4 dedicated tires are also generally stiffer and keep the car higher from the ground than same size "car" type tires.