Tire rotation is the practice of moving the wheels and tires of an automobile from one position to another, to ensure even tire wear. Even tire wear extends the useful life of a set of tires, but the value of this is disputed. Causes of uneven tire wear The differing weight placed on the tires by the front and rear axles 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. In countries with right-hand traffic, for example, right turns are tighter than left turns and most cloverleaf interchanges and parking ramps are right-hand curves, so the left front tire wears faster than the right front, because the left tire travels a greater distance around those turns (the same way that an athlete in the leftmost lane would have to run further around an oval track than one in the rightmost if the race were being run clockwise from a flat line start) and a majority of turns will be to the right. Conversely, the sidewalls on the right tire tends to be bumped and rubbed against the curb while parking the vehicle, causing asymmetric sidewall wear. The symmetric opposite occurs in countries that drive on the left. In addition, mechanical problems in the vehicle may cause uneven tire wear. Wheels misaligned with each other and/or with the vehicle's axis will tend to be dragged along by the other wheels, causing uneven wear in that tire. If the alignment is such that the vehicle tends to turn, the driver will correct by steering against the tendency. In effect the vehicle is constantly turning, causing uneven tire wear. Tire rotation practice Car and tire manufacturers may recommend tire rotation frequency and pattern, typically every 5,000 mi (≈8,000 km) to 8,000 mi (≈13,000 km) depending on the tire manufacturer and vehicle make to ensure even tire wear. A common rotation pattern is to move the back wheels to the front, and the front to the back but crossing