Will shifting to the highest gear as quickly as you can, save gas?

Dear Car Talk

Dear Car Talk | Nov 01, 2008

Dear Tom and Ray:

I have a son who has "gone green." He is passionate about the environment, recycles religiously and is very focused on gas mileage. He owns a '98 Honda Civic. He shifts to the highest gear possible, as soon as possible. (Technical note: On a flat stretch, he may shift to fifth gear at 25 mph and 1,000 rpm, causing the engine to shudder.) Consequently, when he's driving me somewhere in his car, our conversation goes something like this:

Me: "Why are you lugging the engine?"

My son: "Because it saves gas."

Me: "What's the point of saving gas if it destroys the engine?"

Which one of us has the right idea? -- Dave

TOM: You both have some right ideas, Dave. Your son is absolutely right that shifting into the highest possible gear as quickly as possible gives you the best fuel economy. And we commend him for doing his part to help save the planet.

RAY: However, you're right, too, Dave, that if you shift TOO soon, you'll lug the engine, which is harmful to it. And I'm sure your son will agree that throwing away engines isn't a good thing for the environment, either.

TOM: The trick is to shift up through the gears quickly, getting to the highest gear as soon as possible WITHOUT lugging the engine. If you shift up, and the car shudders or pings on acceleration, you're making the engine strain and run hot, and that's injurious. So, if you experience lugging, shuddering or pinging, that's a sign that you've shifted too soon. And next time, you want to stay in the next-lowest gear a little longer.

RAY: You'll find that there aren't hard, fast rules about when to shift; it depends on the conditions. If you're just trying to maintain your speed on a flat road, shifting into fifth gear at 25 mph may be just fine. But if you're trying to accelerate, or climb a hill, you'll probably lug it. And that will eventually take its toll.

TOM: So, give your son a pat on the back for being interested in something bigger than just himself. But tell him to let the car be his guide. If it shudders and pings, it's a sign that he's shifted too soon. If not, then he's hugging trees with the best of 'em.

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