Photo by Rick Geary

As long as they’re round and black, we don’t think much about them.

Matt: I’ve, always wondered why car tires need tread patterns in them. Why is a tire better if you cut designs into them than if they Were just plain? And why are there so many different patterns? — Little Eva, San Diego

Reminds me of the time Uncle Wentworth Alice tried to get backing for a custom tire business. He’d shave off your tread, carve any message you wanted into the remaining rubber, rig your mudflaps to automatically slap on some paint so you could drive up and down the street printing rude messages on the asphalt. His target market was people who had run out of room for bumper stickers but still had plenty to say. As a prototype, he modified the Roadhandlers on Aunt Yunetta’s Escort. But he’d barely rolled out five or six copies of “Eat my exhaust, you pinheads!” when it started to rain, and he hydroplaned into a phone pole. See, the tire tread is supposed to prevent stuff like that.

For all the time we spend Worrying about sound systems and special chrome packages and tinted windows, you’d never guess that the most important parts of any car are its “footprints,” the four hand-sized, elliptical areas where tires meet asphalt. All driving, cornering, and braking forces are transmitted through those spots, which makes tires a critical part of the thrill of the contemporary motoring experience. Tire tread serves to make sure your car actually contacts the road in wet weather. Water isn’t compressible, so with enough of it under foot, a car with treadless tires becomes a boat, floating out of control with no road contact at all. A treaded tire on a wet road pushes some of the water ahead of it, and what isn’t shoved out of the way is forced-into the tread grooves and either thrown out behind the tire or sucked to the side, depending on the direction of the groove. That creates a dry spot in your tires’ footprints so the rubber can actually meet the road. In a heavy rain, at 65 miles per hour, each tire has to bail nearly a gallon of water a second to keep you from surfing the median.

So if a little slice ’n’ dice is a good thing, why not go for the grippiest effect and just shred ’em and be done with it? Well, then you increase rolling resistance and decrease fuel efficiency, create a noisier and hotter tire on dry pavement, and decrease steering and cornering control. All the different tread patterns are the manufacturers’ efforts to strike the best balance and customize the tread according to tire size, vehicle weight, road surfaces, tire composition and construction, sidewall flexibility —- a whole bunch of picky, boring details. Tires actually are one of the most intricate parts of a car. Of course, as long as they’re round and black, we don’t think much about them; then.we counteract all our tires’ carefully engineered advantages by running them at the wrong inflation levels. Incorrectly inflated tires are about as useful as running on four big cream-filled donuts. So make a tire designer smile. Put down the paper right now and go out and check to see if you need air.