When to Replace Your Tires
Tires are the most important performance and safety feature on a car. They are the only patch of contact between that 3000 pound people mover and the road. If you are going to take the lives of you and your family into your car, then you should be able to know your car can safely get you where your going.
Understanding Tire Wear
Tire tread is measured in 32nd of an inch. The best tool for measuring tread is a tread depth gauge. But if you can't get your hand on one of those a penny is a decent substitute. Most brand new tires will be between 10/32nd and 12/32nd for street tire with more for all-terrain tires. Most state laws say tires are legally worn out at 2/32nd. 2/32nd of an Inch is also the height that manufacturers are required to put in a marker, in the form of a wear bar, to let consumers know that they require replacement.
When Should You Get New Tires
Unless you live in an area with no rain, snow, sand, or mud 2/32nds of an inch is to worn out. At 2/32nd your tires have lost most of their wet weather traction, and all of their snow, sand, and mud traction. 4/32nd is when tires need to be replaced (5-6/32nd in more rural areas). 4/32nd is when they start to lose crucial traction in the rain and other elements. When they wear more than 4/32nd the chance of hydroplaning increases drastically, and the odds of sliding on ice and getting stuck in mud or sand become much higher. However, don't fall for tire shop scams, trying to get you to buy new tires when yours still have plenty of life, all reputable dealers will have tread depth gauges you will be able to watch them use.
Which tires, Where to Put Them, How Many To Replace
If you have one tire go out on your vehicle go ahead and check the tread wear of all four of them. If they are close to new (between 12-8/32nd) then replacing just the one is fine. If the tread depth is less than that (between 7-5/32nd) you should replace the bad one and the most worn tire left on the vehicle. You would replace two to make sure the amount of traction is even over the wheels. If they measure less than that (between 4-0/32nd) it is time to replace all 4.
Whether you decide to replace one tire or two make sure that the new equipment is put on the rear of the vehicle. When a car slides or hydroplanes the rear of the vehicle is always the first to go so you want your best possible traction on the rear wheels.
Tips and What to Watch Out For
If your vehicle is an all wheel drive car it is crucial that both front and both rear tires measure as closely as possible to avoid lose in handling and uneven tire wear. It is also necessary in an all wheel drive vehicle to have the same brand and model of tire on all four wheels to prevent an uneven distribution of your handling, traction, and tire wear.
If you have mud terrains all of these wear measurements will be different, this guide only applies to street and light-terrain car/SUV/truck tires.
When using the Penny method insert the penny into several spots along the tread upside-down
2/32nd - The very top of Abe Lincoln's head
4/32nd - Where is hair meets his forehead
7/32nd - the top of his ear
10/32nd - the bottom of his nose
12/32nd - the start of his bread just below his mouth