It's tire season again and with the early snow we receive a lot of questions about tires. One questions we receive a lot is 'Why do I need to do all four tires on my XXX?' The rule we follow here that decides if we can replace one tire, two tires, or all four depends on several factors. The tire condition/age is an important one. If we have tires that are over ten years of age and showing increased signs of degradation we will recommend a minimum of two on a tire replacement visit. Tread depth is another prime factor. Tread depth can not vary more than 2/32" from side to side on 2wd vehicles or front to rear along with side to side on AWD vehicles. This is due to friction. With tread depth on new tires being around 10/32" you decrease the diameter on each tire as the tire treads are consumed by driving. A tire with a smaller diameter must spin faster and have more revolutions to travel the same distance as a new (larger diameter) tire. On FWD vehicles, the two front tires are connected by CV Axles and a Transmission. The Transmission is designed to allow one tire to rotate faster or slower than the other side when turning during instances of sharp, sudden turns or slick surfaces but they are not equipped for constant or extended uneven rotational distances created from uneven tires. The result is transmission wear. On RWD or AWD vehicles your rear differential has gears that are designed for normal driving conditions and smaller, spider gears for turning. If you mismatch tread more than 2/32" on the rear axle or on an AWD vehicle those gears will engage the entire time when driving not just when turning as was designed. This creates friction and thus heat. This leads to gear failure and a couple of tires is ALOT less money than a rebuilt Differential. Additionally, on AWD vehicles it is important to take care of those tires through inflation, rotation, and balancing. At Tuffy Ankeny we provide the best plan to help you achieve the greatest life out of your tires! Stop in and ask us about our Tuffy Tire Protection Plan!