【英语时差8,16】耗油卡车（下）

（单词翻译）

 Here's why. A closed tailgate sets up a bubble of air that slowly circulates in the bed of the truck. Air coming over the cab of the truck treats the bubble as a smooth cover over the bed, and passes over this “cover” without ramming¹ into the tailgate. Opening the tailgate breaks up this smooth bubble of air. The air then rushes over the cab, and quickly down into the bed. This creates a lot of turbulence², which results in more drag. So technically³ speaking, with the tailgate open the shape of the truck is not as aerodynamic as it is with the tailgate closed. So, gas mileage⁴ is better with the tailgate closed. Actually you probably wouldn’t notice much improvement at lower speeds, but at highway speeds of sixty miles-per-hour and above you should get slightly better mileage. Also, the truck is structurally⁵ stronger with the tailgate up, so that’s two good reasons to keep it closed. Well, maybe a third would be to keep the trash you’re hauling from spilling onto the road, but that’s another story.