SASprof

Sure, CC can hold a steady speed, which is good for MPG. However, if you need to slow down, and it's not an emergency, most of us will just let off the throttle for a bit. Alternatively, if you use the - button to have CC slow you down, CC will apply the brakes, which hurts MPG, right? Similarly, when going downhill for a stretch, most of us will just let off the throttle and (traffic permitting) allow our speed to creep up slightly, which is great for MPG. But, in that same situation, CC will apply the brakes to maintain speed, killing MPG. So, for best gas mileage, avoid CC, or use it only on perfectly level or uphill stretches and never use the - button. Am I right?

Bucknut2006

I've never seen CC apply brakes. Is this something new or unique to the C7?

CaryBob

Must be. The C6 absolutely does not apply brakes on cruise control. The throttle cuts on and off in an effort to maintain speed on a downhill, and that might feel like braking, but it's not. A glance at the revs will tell the tale.

Bigredwing

I actually did an unscientific test of this in my Silverado using the trucks estimated mileage as shown on the DIC. The truck is a diesel and I was on I95 heading to Florida. It showed I saved about 1mpg using the cruise, but that is also based on my driving habits.

1SG_Ret

Agreed, I find it reacting like taking your foot off the accelerator if you shut cruise down or touch the brake pedal. I'll use the + or minus to vary speeds with the cruise.

However, on resume, (if you are significantly slower than the resumed speed), some cars accelerate hard to get back to the cruise speed which IMO hurts mileage.

Living in Florida we have nothing but flat.

Haven't gotten my C7 delivered yet, but that's how it works on my Santa Fe.

BRCC

CC in the C7 does not apply the brakes, when you release CC (The button) compression slows you down, same situation going down hill.

JerryU

You’re right and wrong! The C7 does not apply the brakes when going downhill. However you’re correct in that the best gas mileage is not using cruise control, unless the entire road is perfectly flat. Even on a small hill the accelerator will increase to maintain speed. Best to just keep the throttle in a fixed position and let the car slow and when going down a slight incline let it increase in speed. The old throttle cable I had in my ’50 Ford or perhaps it was my ’41 Ford coupe is actually better although not ideal either.
I recall when we could only fill up with gas every other day in late 1979 as I recall, having a bet with my car pool buddies that I could get 50 mpg with my new Dodge Colt. It normally was getting about 40 mpg on the highway. I had installed a mpg meter in the car, which was pretty accurate. We started in a somewhat hilly area and I let the car slow going uphill. The Colt had a two speed overdrive with two shift sticks and I keep it in 7th. It made a few folks unhappy behind me as I recall but it did keep the mpg up. On the downhill I put it neutral and let it cost and let it increase in speed! That is not safe but worked! Did the same all the way on the Sawmill River Parkway with its twists and turns, ups and downs! Took us longer to get to work but I won the bet!
There was a race, called the Mobile Economy Run. If I recall correctly you were not allowed to use a vacuum gauge. That is probably the best tool to help get optimum mileage!

EasyElliott

See what happens when people who never drove a vet write a thread.
Must be a BMW owner as my BMWs apply the brakes going down hills. So on those cars I shut the Cruise going downhill.

My C6 Did not apply the brakes nor does my 2015 C7

NSC5

I also have a Sierra diesel and the only place where the cruise control doesn't save fuel is in rolling hills where unloaded it tends to overshoot a bit midway uphill and ends up going maybe 1 MPH faster than set speed and then over-corrects on the downhill. But it does fine on longer grades and only in a series of rolling hills does this behavior become obvious. When heading down to TN/NC a use a short section of US 136 in otherwise flat IL where this behavior is very noticeable. The only other annoyance with CC on the Duramax is it maintains speed easily on long steep interstate grades and will try to run over vehicles in front that don't maintain speed as well, usually staying in the left lane on grades avoids the problem

I would be surprised if the CC is applying brakes but on many (maybe all) of the newer GM vehicles the throttle release to idle is more abrupt so compression braking (really braking caused by engine trying to pull air through a closed throttle plate) is much more noticeable. My 2014 ATS has noticeably different coasting behavior than the 2008 CTS it replaced. A number of newer vehicles with automatic transmissions will also downshift automatically on grades when CC is active to maintain set speed.

gkgeiger

If your CC is set and you go down a hill that would cause the car to coast and speed up, the transmission will down shift to the the necessary gear to get you back to the set speed. Try it, watching your tach.

millpond

True this.

W88fixer

Think the idea that CC applies the brakes is BS. Hit the - button and the car just gradually slows. Used properly, CC will do better than any human 98% of the time.

If you want to play games, you can turn CC off and use your kinetic energy to go over a hill for example and gravity to regain speed on the other side. In that case, CC won’t help, it’ll try to keep the set speed.

If you’re cruising, use CC. Works great, less tiring for the driver. Don

W88fixer

What matters there is not that you got 1 mpg better but what is the percentage improvement? If you got 1 mpg over a normal of 12, that’s an 8% improvement. 1 mpg over 26 mpg that is quite realistic on the C7, that’s a 3.8% improvement. Don

SASprof

Thanks to everybody for correcting me. Seems CC does not apply brakes. Good to know.

If CC uses compression, rather than brakes, to slow you down, as some have said, won't that have the same effect on gas mileage, wearing your engine to save your brake pads, but still hurting your gas mileage?

fsvoboda

I suspect that if you're being insanely attentive you might beat the MPG you get with cruise control, but for most ordinary highway driving you'll do better with cruise control.

69L79

As a Vette owner/driver for over 46 years I would advise that obsessing over a few miles per gallon will kill your enjoyment of these great Cars.

Steve_R

If you're really that worried about small differences in gas mileage perhaps you should have bought an econobox, not a Corvette? Even if there is a 1 or 2 mpg difference on a long trip between using CC and not, who cares?

fsvoboda

You know, I sort of thought the same thing at first, but on reflection decided this discussion really is just another side of discussing C7 performance, which is a common topic here on the forums.

EasyElliott

I agree that on my old C6 and my new C7 cruise control does not apply the brakes.
But on my 2 new BMWs 335I and 435I if you are set at lets say 70 and click decel more than 5 mph it does apply the brakes to get it down to speed.

In Colorado going down the hills if you did not shut the cruse it would just keep the brakes on.

To prove it my wife followed me and the brake lights came as this happens. I do not know about a lot of other cars, but I have never seen this to happen on GM Ford Toyota Chrysler or Honda Vehicles.

But it does happen on BMWs at least 2012 and newer.

SASprof

Exactly. Thank you. Just trying to understand the CC, it's pluses and minuses. Minor convenience. Possibly a minor cost.

Overall, I'm ecstatic with my C7, and ecstatic that it gets about 5MPG better than my beloved C6 on the highway: 34 vs 29.

Around town, who cares. It's a muscle car when I want it to be and, yes, an econo "box" when I'm cruisin. One hell of an econobox, I might add.

Remember, Chevy added an Eco mode. I, for one, am glad they did. Along with all the other great things they added to this fabulous car.