The differing weight on the front and rear axles differs which causes uneven wear. With the majority of cars having the engine in front, the front tires typically bear more weight than the rear tires. Front-wheel drive vehicles have not only the engine but also the transaxle in front, adding to the weight difference. Moreover, additional stress is placed disproportionately on the front tires by braking and steering. Thus, tire rotation needs to occur more frequently for front-wheel drive vehicles.
Turning the vehicle will cause uneven tire wear. The outside, front tire is worn disproportionately.