Dear Tom and Ray:
Whenever I am driving, my dear husband and I have an argument about fifth gear. I was taught not to use fifth gear unless I am going to be driving on a long stretch of road without traffic lights or I am on the freeway (we have a 1998 Volkswagen Passat). My husband says it doesn't matter how long you're going to be in fifth gear; he says it's all a matter of how fast you are going. He says I got a simplified explanation because I'm a girl. He goes from first gear to second to fifth driving around town, even though there might be a stoplight a quarter-mile away. He says that he rarely uses third and fourth gears (which I use all the time in the city) unless he is hauling a load. Ease my troubled mind: Is this causing stress on our transmission? -- Mary
RAY: Forget about the transmission, Mary. I'm more worried about the stress it's causing in your marriage.
TOM: Let's start with a freshman seminar: Fifth Gear 101.
RAY: The first thing you need to know is that it's easier to KEEP a car moving than it is to GET a car moving. In other words, getting a car from 0 mph to 50 mph takes a lot more effort than keeping it going at 50 once it's already there. Newton figured that out after he invented the fruit-filled cookie.
TOM: So, the gears in a car are designed for various degrees of difficulty. First gear, for instance, is designed for the hardest work, when you're moving a car from a dead stop or climbing a steep hill. In first gear, the engine's crankshaft may turn 100 times for every rotation of the wheels.
RAY: If you've ridden a multispeed bicycle, it's very similar. You know that in first gear, your legs (like the car's engine) pump the pedals many times, even while the bicycle wheels turn very slowly. But the pedaling is very easy on your legs. That's like first gear in a car.
TOM: And like high gear on a bicycle, your car's fifth gear is designed for the easiest duty, when you're already at speed and just need enough power to keep the car moving at that speed. So in fifth gear the engine just lopes along, turning the crankshaft only, say, 25 times for every rotation of the wheels. And that saves gasoline.
RAY: So, when should you use fifth gear? As often as possible -- as long as you're not "lugging the engine."
TOM: By "lugging," we mean that the engine is struggling to accelerate. How would you know it's struggling? Because when you step on the gas to accelerate, it doesn't go faster. It might bog down, it might buck, it might lurch. And you might get noises from the engine, like pinging or knocking. If any of those things are happening, you're going too slowly to be in fifth gear, and you need to downshift.
RAY: So, to address the dispute with "dear husband," Mary, it turns out you're both a little bit wrong. It makes no difference how long you plan to stay in fifth gear; the engine or transmission couldn't care less. So that's not a criterion for when to shift.
TOM: But "dear husband" is also off-base when he says that speed is the only factor. After all, you can shift into fifth at a lower speed while going down a hill than you can on a flat road. Speed is a good guideline, but the bottom line is, if the engine isn't complaining, you're good to go.
RAY: And by the way, your driving style is absolutely fine, Mary. The only potential downside to avoiding fifth gear in town is that you'll get slightly lower mileage than perhaps you could. But you'll do the engine absolutely no harm by driving in third and fourth around town. In fact, you're sure to avoid lugging it.
TOM: And as long as "dear husband" is not shifting so soon that he's lugging the engine, his style is fine, too. But if you hear the engine pinging or feel it bucking, then reach over and give him a dope slap. Or write him a "dear husband" letter.