Check Your Tires Before Your Holiday Road Trip
The most important part of your car is where the rubber meets the road.
The time between Memorial Day and Labor Day is considered one of the most dangerous times to drive during the year, according to AAA. Paying attention to your driving is, of course, an important aspect of staying safe on the road. But just as important are the tires on your car. The rubber that meets the road can completely transform your car's handling and performance, for better or for worse. The Drive spoke with Ron Margadonna, senior tire technical manager for Michelin, to gain some insight into those black rubber circles at the four corners of your car.
Regardless of the brand or type of tire you use, the most important aspect is tread depth. Bald slicks are great for the track, but on the street, a tire with low tread loses significant traction in the wet. Margadonna recommends an absolute minimum tread depth of 2/32 inch. If you don't have a tread depth gauge, stick a penny into your tread upside down. If you can see the top of Abraham Lincoln's head, it's time to replace your tires.
AAA disagrees with Michelin's suggestion, however. AAA's own testing showed that even at a tread depth of 4/32 inch, worn tires could still increase the stopping distance of a passenger car by up to 87 feet and reduce a driver’s ability to control a vehicle by 33 percent. You can use a quarter and George Washington's head to measure 4/32 inch in the same manner as a penny and Lincoln's head.
Either way, low tread depth is bad news in the rain. I got to experience this for myself at an autocross event where it was dry for most of the day, then the sky opened up for my final run. I was running well-used R-compound tires on my Mazda Miata, which were essentially slicks at that point. I'd been running the day's course consistently under 60 seconds. But thanks to standing water on the old runways at the former Fort Devens (fortunately not on a public road), it took all my skill just to keep the car from spinning out. My time: 73 seconds, driving on the ragged edge of my limited wet traction the whole time. That's more than 13 seconds slower on a one minute run, just because my racing tires had no tread.
Back to the road, another important aspect of maximizing your tires' safety and performance is tire pressure. Every car has a placard, usually on the driver's door or door jam, specifying the front and rear tire inflation pressures. Sometimes they are the same, but often they are not. Regardless, make sure your tires are inflated to these recommended pressures.
Modern cars have a low tire pressure warning system, which lights up a warning on your dashboard when one or more of your tires is low. But don't rely on this. The right front tire of my Subaru WRX has an extremely slow leak, so slow that once a month it deflates enough to trigger the warning light. The recommended front tire pressure on this car is 33 pounds per square inch. When the warning comes on, the tire is down to about 27 psi. So I really need to check it once every week or two to make sure it doesn't get too low.
Make sure you are setting your pressures while the tires are cold, too. Tires heat up while driving, so if you park and set pressures immediately afterward, your pressures will actually be too low after the tires cool down.
Ignore the pressure printed on the side of the tire. This number is the maximum pressure the tire is designed to handle. It is not a recommended pressure in any situation.
There are additional factors to consider when it comes to your tires. One is how much weight you're putting into your car. Every vehicle has a Gross Combined Weight Rating (GCWR), which specifies the maximum total weight rating of the vehicle, passengers, and cargo that it can carry. For one person commuting empty to work this is not a concern, but when you load up the whole family and everything you need for a week of camping, it's possible to exceed this limit, which can lead to a loss of control even at ordinarily safe speeds.
Of course, driving habits also play a role. Particularly when loaded down, make slow, cautious lane changes, because the car won't react as well to abrupt movements. Maintain a safe following distance, especially when it's wet because of the longer stopping distance than dry conditions, no matter how good your tires are.
An ongoing debate is whether you should use separate tires for summer and winter, or whether using an all-season tire year-round is adequate. For summer driving, all-season tires will do the job just fine. But consider that a dedicated summer tire will do the job even better. Summer tires are optimized for dry and wet conditions and higher temperatures. They also have no design compromises to accommodate cold or snowy conditions. As a result, contrary to what some believe, a dedicated summer tire will actually work better in the rain than an all-season tire.
When it comes to running two sets of winter and summer tires or all-seasons year-round, Margadonna suggests that if you live in an area that gets light to moderate frozen precipitation, or moderately cold temperatures, an all-season tire is fine. But if you get both moderate precipitation and cold temperatures, you should consider switching to a winter tire when the temperature drops, then run summer tires optimized for summer conditions.