My wife has concluded that she gets better mileage if she uses cruise control. I wonder if there is any difference mileage-wise if one uses cruise control or maintains the same speed “manually”. Your thoughts? Further, with respect to the car’s mechanics, what are the pros/cons of using cruise control versus not using cruise control?
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None , the car does not care either way.
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She probably does get better mileage with cruise control, very few people can maintain their speed as steady as the computer can.
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I have proven to myself that I can get better mileage using my foot than cruise control… BUT… it takes a LOT of concentration and I can’t maintain a steady speed if I want to beat the cruise control.
Most normal drivers, and me (if not paying very close attention) find cruise control to give better mileage. It doesn’t hurt the car in ANY way.
If more people would actually use their cruise control, traffic would flow much better by eliminating the gas pedal pumpers who cannot maintain a steady speed to save their lives!
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I rode with a guy like that once, I felt like I was going to get sea sick.
Accelerate to 70, coast to 60, accelerate to 70, coast to 60.
That was the longest 180 mile trip I think I’ve ever ridden in a car.
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A dedicated hyper-miler can beat the gas mileage of cruise control, but not ny holding the speed steady. The hyper-miler slows gradually going uphill, gains speed slowly downhill, uses a light throttle to get the car to up shift early to to be, in the highest gear possible, backs off the gas way early for a red light so he can hit it not only as it turns green , but after the traffic has moved away and they will switch lanes repeatedly rather than brake. In short,everything they do will will drive the people around them crazy.
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I can definitely identify with your sentiments!
Some of you may recall my nutty former boss, whom we nicknamed “Chatty Cathy”.
He loved to talk–almost non-stop–and every time that he spoke to his passengers while he was driving, he would look at the passengers, and simultaneously hit the brake. Then, when he looked back at the roadway, he would hit the gas to compensate for losing momentum during his last monologue. Riding with him was–literally–a nauseating experience! 
Incidentally, this was the same guy who would only put a few bucks worth of gas into his Buick at a time, because, according to him…
If you tell them to fill it, that’s when they can cheat you.
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I do everything you mention except “switch lanes repeatedly”, but I disagree that I “drive the people around them crazy”. I think my “hyper-miler” habits are much less offensive than the always-in-a-hurry-tailgater types.
I suppose you are mostly right that my style does annoy a lot of people though.
Use the cruise. If it saves you from one speeding ticket, you win. And the drivers that squeeze every stinking mile per gallon from their Prius and creep up hills, don’t go when the light changes and linger in the left lane so they don’t have to worry about slowing and speeding up just irritate the rest of us and cause much more unhappiness than their selfish adventures are worth.
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They’re less aggressive, perhaps, but they’re also annoying. If you’re that invested in saving gasoline, get an electric. Taking 3 minutes to accelerate to boulevard speeds is a great way to enrage everyone behind you.
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Of course I don’t accelerate anywhere near that slowly, and I’m not just about saving gas. I drive very gently to preserve the entire car including the tires. I figured out decades ago that there is nothing worth hurrying for.
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I like using CC on long freeway trips, like I80 across remote parts of Nevada. I think I get a little better mpg using it compared to not. But I’d get significantly better mpg just driving 5 mph slower. From the point of view of a diy’er who fixes their own car, I prefer a car configured w/no cruise control. It’s just a bunch of stuff in the engine compartment that often gets in the way. And when CC fails it can produce symptoms that are difficult to diagnose. And it often contains expensive to replace components, sometimes hard to source on older cars.
I’m not saying this issue is at the bottom of my list but it’s so far down I can’t see it. Just drive and be happy. At any rate it is not maintaining a constant speed, it is maintaining a constant throttle that gives the best mileage. Obviously you can’t do that without driving everyone crazy as you slow on hills and speed down hill. Yeah you can probably do better than cruise but is it worth the 15 cents you’ll save? Just let your wife do what she wants.
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Tom and Ray Magliozzi have insisted, several times over the years, that the computer that controls the cruise control is infinitely better at maintaining a constant speed than a human driver, and this amounts to meaningful fuel savings, particularly on long trips.
Personally, I use cruise control to stay out of trouble. I like to set it at the speed limit, or 5-10 MPH over the speed limit, depending on the flow of traffic, because when I operate the throttle manually, my speed always creeps up. I’d much rather camp out in the slow lane with the cruise control set at 75 MPH in a 70 MPH zone and let most of the cars worry about passing me than edge up to 80-85 MPH and constantly change lanes to pass others. Letting others worry about passing is much more relaxing when you’re not in a hurry.
As to whether you should use cruise control, fuel economy isn’t everything, so if you would rather leave it off and manually operate your throttle, leave it off and manually operate your throttle. If your wife wants to use the cruise control when she drives, she can do that, but only one person gets to drive the car at a time, and unless the driver is doing something that is unsafe, the passenger should do her or his best not to be a side-seat driver.
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What you’re describing sounds a lot like a throttle lock on a motorcycle, which is certainly more fuel efficient than cruise control, but installing a throttle lock on a motorcycle’s throttle control is a lot easier and a lot safer than installing a throttle lock on a car.
Then you’re not a hyper miler. 
I always thought they weren’t sufficiently nuanced in that statement, though. It really depends on the terrain and the cruise control. Older cruise controls behaved more like throttle locks. Whereever the throttle was to keep you at X speed was where the throttle stayed, which meant you slowed to a crawl going up hill and did about Mach 4 going down hill.
Even a lot of newer CC’s are good at not dropping below the set speed, but if you drive down a hill they won’t downshift or apply the brakes, and so you end up going a good deal faster than the speed limit by the time you hit the bottom.
On flat terrain, sure, pretty much every CC is going to be better at maintaining steady speed than a human. Any other time, it really depends on how well the CC is designed.
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Tom and Ray? Nuanced?? Thanks for a good morning laugh 
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Well, yes, but in this case they’re being used as evidence to further a statement of fact and so consideration of whether or not their comments are fully accurate is appropriate.
I only learned to drive in 1989, so I don’t know how far you’re going back when you say “older cruise controls,” however, I always attributed to that behavior from cruise control, where it slowed down going uphill and overcompensated once you crest that hill, as being a lack of power.
With under-powered four-cylinder cars from the 1980s, when the car went up a hill with the CC engaged, the automatic transmission would often downshift into passing gear the same way it would if you mashed the throttle manually, and on some cars, like a Dodge Neon or Ford Escort, that wouldn’t be enough to help it get back up to speed going uphill. If you were driving a manual transmission four-cylinder car from that era, it would just struggle and slow down going uphill with the CC engaged.
With a small under-powered car from that era, the only way to make it up a hill without slowing down would be to accelerate before getting to the hill. This is one of the major reasons that, when I bought my first non-hand-me-down car, it was an efficient four-cylinder car that was light enough and powerful enough that it could actually accelerate going uphill.
One last thing: Hilly driving usually has lots of twists and turns, which are conditions I wouldn’t use CC in for the sake of safety, unless I intended to set the CC at a safe slow speed. Driving through twisty roads at a constant speed can be hazardous, so I don’t use CC in those conditions anyway.
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Tom and Ray had good reason to ignore nuance: Their target audience was the uninformed automotive consumer, not professional and shade tree mechanics. Also, on a radio show, nuance can bore your listeners to death. That’s why there are thousands of podcasters out there with dozens of subscribers, because they focus too much on minutiae.
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