Many readers have asked questions about tires because they are a big expense and they want to have some basic information before venturing out to a tire retailer. Here are two of the most frequently asked questions and answers for them.
Question:
Do I have to purchase four winter tires for my rear-wheel drive truck? The tire store says that this is needed.
Answer:
Although it may sound like a scam by the tire store to get you to buy an additional two tires, their recommendation is valid. Putting winter tires on the rear of your rear wheel drive vehicle will indeed help you pull away from a stop sign or get up your driveway easier. Most winter driving accidents, however, not are caused by an inability to get up to speed, but from either not being able to stop or failing to make a turn and hitting a curb, ditch, or another vehicle. Even on a slick snow covered road, which causes less load transfer under braking, there is still over 50% of the braking force coming from the front tires. Putting only winter tires on the rear of your rear wheel drive vehicle is a good way to end up in a ditch the first time you attempt to turn, or lulled into thinking you can drive faster than you think. Gut wrenchingly, you find you now cannot stop or make the next turn.
OK, so you have a front wheel drive vehicle, why not just put winter tires only on the front? Now you can go, turn, and stop, right? Again, you have created a situation where one end your vehicle is writing checks the other end cannot cash. When you turn the wheel for a curve, the front tires will be able to generate much more corning force than the rears, potentially resulting in you ending up in a ditch again, but back end first this time. It is important to keep all four tires within the same performance category, whether they be winter, all-season, or summer tires.
Question:
I have own an all-wheel-drive Subaru and I had a cut tire on the right front. The tire store tells me I have to purchase four new tires because there are 20,000 miles on my vehicle and that all four must match. Is this right?
Answer:
As tires wear down, the overall diameter becomes smaller. At a given speed, a worn tire will turn faster than its equivalent new version. On all wheel drive vehicles such as your Subaru, this difference in rotational velocity can cause premature wear of the drive line differentials over several thousand miles. An alternative to replacing all four tires (or two, as some manufacturers only require that each axle match in diameter) is to buy only one new tire and have the tread shaved off to a depth that matches the other tires. Many larger tire stores can offer this service, as well as the online retailer TireRack.com.
