时差N小时:轮胎上为什么有胎纹?

If you've ever driven on a highway during a heavyrain, you know about the danger of skidding. This"waterskiing" on the road is technically calledhydroplaning, and it happens when water comesbetween the road and your tires, causing you to losetraction and go out of control. Your car is less likelyto slide around when the road is dry because thereis enough friction between your tires and the roadto keep you steady, even at high speeds.

如果你曾大雨天开车在高速公路上行驶，你就会知道打滑的危险。在技术上，这种“路上滑水”称作“湿路打滑”，当路面和轮胎之间有水时，就会发生这种现象，致使车子失去牵引力从而失去控制。当地面干燥时，就不可能打滑，因为轮胎和道路之间有足够的摩擦力来使车子在高速行驶时保持稳定。

But when it rains, a layer of water builds up between your tires and the road. This waterinterferes with the friction that helps your tires grip the road surface. This is where the treadson your tires come in. If the road you are driving along is covered with water, the pressure ofthe tire against the road surface causes the water to be squeezed up into the tire treads. Thesetreads help your tires pump water out from underneath the tire so that the rubber can be incontact with the road, thus creating the friction that will stabilize your car.

但是当遇到雨天时，路面和你的轮胎之间会积起一层雨水。水会减小摩擦，而摩擦力的作用正是帮助加强轮胎抓地力防止其失控。这时轮胎上的条纹就起作用了。如果你一路上驾驶的道路被水覆盖，轮胎对地表施加的压力把积水挤压到轮胎面上。这些纹路会帮忙把轮胎下的水抽出，这样橡胶就又能与地面接触，从而产生阻力使你的稳步前进。

The faster you go, the more water your tires have to remove. That's why your car may nothydroplane at thirty miles per hour, but might at sixty miles per hour. In fact, at highwayspeeds, during hard rains, each tire must pump away about a gallon of water every second.This is hard for tires to do if they are old and have treads that are worn down. When there isn'tenough space in the tire's grooves, water can't find a place to go and so it creates a layer oflubrication, causing you to do the equivalent to waterskiing on the highway.

你开得越快，轮胎需要排出的积水就更多。这就是为什么你的车时速30英里时不打滑，而时速60英里时却打滑。实际上，按照高速公路上的行驶速度算的话，在雨天每个轮胎每秒要排出一加仑的水。如果轮胎太旧或者已经严重磨损的话，排水就会很困难。当轮胎凹槽上的空间不够时，水无处可去，就充当了润滑层，造成车子打滑，就相当于在高速公路上做滑水运动。