Is it true you get better gas mileage using cruise control? Why?

Dear Car Talk

Dear Car Talk | Jan 01, 1996

Dear Tom and Ray:

I recently purchased a '95 Ford Probe. Cars certainly have come a long way since I last bought one 13 years ago. I'm new to cruise control, but it didn't take very long to be sold on it. However, I have a couple of questions. First, several people have told me that you get better fuel economy while using cruise control. Really? If so, why? Second, if I know I'm going to be off cruise control for a period of time (for example, when I'm going through a town), does it matter if I turn off the "main" cruise control switch on the dashboard? Is there any difference between having it actually "off" and just "not operating at the moment?"

RAY: First of all, Rob, congratulations on entering the modern era. Cars HAVE come a long way in the last couple of decades. Anyone who questions that need only look at my brother's Dodge Dart. How's the cruise control on that baby, Tommy?

TOM: You mean the cement block I rest on the gas pedal?

RAY: You probably do get better mileage with cruise control if you're driving on long stretches of reasonably flat roads. That's because cruise control keeps you at a constant speed.

TOM: It takes more gas to speed up than it does to maintain an even speed. And when most of us drive, we inadvertantly slow down, speed up, slow down, etc. It takes a lot of concentration to stay at a steady speed without cruise control. But with it, it's no problem at all.

RAY: By the way, for you teenagers in the audience today, when we say you get better mileage when traveling at a steady speed, we mean a REASONABLE steady speed. You're not going to get better mileage driving at a constant 80 mph than you would by fluctuating between 50 and 60.

TOM: But I wouldn't use the cruise control just to save gas. The benefit is probably marginal. The real reason to use cruise control is so you don't get cramps in your right leg!

RAY: And you SHOULD turn off the "main" cruise control switch on the dashboard when you're not going to be using it for a while. The "set" switch is on the steering wheel or stalk of most cars, which is great because it's very convenient. But it's also easy to engage it accidentally. That's why there's a harder to reach "main" switch on the dashboard. So, yes, turn it off for safety when you're not on the highway to prevent accidental engagement.

TOM: I had an accidental engagement many years ago. And I'm still paying alimony.

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