Cruise Control

Depends on the terrain. On flat ground, CC is probably usually a good thing for mpg. On hilly terrain, all automatic transmissions suffer with CC because the CC can't anticipate gravity-assist like the driver can. Redline acceleration just before the top of a hill doesn't help mpg.

Presumably using ECO mode lets the mph vary slightly in CC to help mpg, but I'm still not convinced.

 

In the little highway driving that I have done, I had better success going without. However, a lot of my "highway miles" are hilly, so it often pays to lay of the accelerator on an incline and let gravity get you back up to speed on the decline.

 

On my Prius I don't use the cruise a lot , I don't think it helps my MPG!
I like to keep my foot on the gas and keep it as light as possible when I'm trying to save fuel. But otherwise I just use the cruise!
Try it and see what works for you! I think on a long trip it's the same.

 

I think CC with ECO mode gives the best MPG's. As long as the highway is fairly level and you're not in the Colorado mountains ...

My cruise control is the best I've ever experienced .... when I set it at a number ... very rarely does it change from that number. I love it. Last trip I achieved 55.9 MPG on the highway ... on a brand new engine in cold weather.

REV

 

At what speed were you cruising at? I'll be taking a road trip soon in mine and so I am wondering what I should set it at. The speed limit where I am going is mostly 70 mph (5 freeway through central CA).

 

One thing I have only briefly tried is to set cruise control and then as I am climbing an incline/hill, I would cancel cruise by pulling the CC lever towards me and once I go over the top, then depress the pedal a little to glide/accelerate while coming down the hill and then set the cruise again. Alternatively, the CC speed can be reduced in quick "coast" clicks in succession as the car is going up the hill and then once over the top then the CC speed can be increased again in quick "accelerate" clicks in succession.

 

Sorry about the delay. Generally speaking I drive the exact speed limit. It it's 55, then 55, if it's 65, then 65. The trips I was speaking of was from Eastern PA to OC MD ... about 220 miles, which used just under 4.0 gallons. About half and half 55, and 65.

REV

 

There was a post on another thread saying that the car changes speed a lot in CC but the numbers tend to be sticky (I guess to make the driver happy that the speed isn't changing). They measured as much as a 5mph difference (lower) with their GPS from what the speed indicator was saying, but it varied all over the place.

 

My $0.02...

I live in a fairly flat area. My driving routes vary considerably from day to day but there is one office 35 miles away that I drive to consistently enough to try to quantify some mileage deltas for some of the wild claims that I've heard about mileage killing items like cruise control use, Eco mode, tire over inflation, E0 gas, etc...

My boss (also G3 equipped) claims that he gets better mileages without the cruise control, but I haven't seen this in 3 separate runs to that office (1 with, 2 without.) My GPS says that the VSS tracks with the GPS speed without much dithering. My cruise stays locked pretty much dead on the target speed---although I wish that there was an "eco-cruise" that would allow for more moderate accelerations on the few hills that I encounter down here. (Are you listening Toyota? When you get finished with the rattles and the brakes...)

If you have to run a laboratory style experiment to quantify a 0.05236% delta in fuel efficiency, then (for me) it's not worth bothering with. I can report that my very unscientific observations tell me that you can get about a 2MPG bump in efficiency by overinflating your tires by about 20-percent, but I haven't noted any huge differences by using E0 gas, or any difference at all by taking the car out of Eco mode for a half a tank or so. I'm unwilling to draft or block my grill(s) for obvious reasons.

TIFWIW...... I personally think that if you're a lunatic hypermiler, you might get as much as a 5-percent delta by disengaging the cruise control in areas that are more topographically diverse than the Redneck Riviera. It's probably less than one percent here.
Me personally? I drive the car, not the other way around. I save where I can, but I'm gonna keep using my Cruise.

 

I just took my first trip. I went from Durham, NC to Richmond, Va. On the way, I was trying to work with the hills without the cruise. I was doing okay but then switched to cruise. I actually got my best mpg (average of 55 mpg and 75 mpg in one five min interval). On the way back, I just started with cruise. I actually got a LOT worse. I am wondering if I need to get things started.. perhaps you "train" the cruise. I normally just leave it on "normal" versus ECO. I may try ECO on the next road trip.

I find ECO a bit unresponsive for around town.

Ray

 

Nah ... you just experienced a terrain variation.

My cruise usage is pretty much on flat land. One thing I HAVE noticed though, is that from my home in eastern PA (1000 feet elevation) to OC MD (0 feet elevation), I typically get around 55-56 MPG for the trip, where on the reverse (0-1000 feet elevation) I typically get about 52-53 MPG. Even though that elevation difference is over a distance of 220 miles roughly, it seems to matter, because it's happened every single time now (4 times). Makes sense, just surprising that that much of an elevation change over that many miles would really matter.

REV

 

I have two trips on my PII so far, the first was a 270 mile round trip and the car was one day old from the dealer, I used Cruise Control both ways with some moderate hills and averaged 46-48 up and back. I really like the CC with this car and was surprised at how well it accelerates and holds speed with ease. The second trip was 6 days later and 150 miles round trip on the same hwy and I started out with CC like I always do but then decided to use the pedal.
I averaged 50-55 but I was driving much slower speeds using the eco tips found on this forum for better mileage. With CC I set it between 70-75 mph and with no CC I was driving at 60-70 mph, it was a much more comfortable drive with the set it and forget Cruise Control on. Both my wife and I really love our Prius, how it drives and is saving us 400+ a month with the lower fuel cost and lower monthly car payment. Coming from a full size SUV that we rarely used the full potential of having a SUV, the Prius is just what we need.

 

Kudos on giving up the SUV. We parked the minivan (DH drove it) because we seldom use its full potential (18 mpg, and burning oil). I see so many moms out there picking up one child, idling an SUV the size of a small house, running the AC, windows up, in beautiful comfortable weather. Now I can twice as big because I get 57 mpg AND I never idle on gas! Now you can bigger too!

 

On long trips I use cruise control. To me its worth it
because it far more comfortable after hours of
driving.

With are Prius loaded down with three people and luggage at 70 + MPH we still averaged over 48 mpg with cruise control. Probably without it it would have been 50 Mpg.

Of course, drop the speed down to 60 mph and you are well over 50 mpg, calculated of course.

alfon

 

we used CC on Pennsylvania turnpike and to my surprise it delivered better MPG then non-using it, 51 vs 46 on the same route.

Prius CVT does much better then regular automatic b/c it will choose optimal ratio for any road pitch, much better then you can manually, and CC will use battery on uphills and downhills for regenerative. I suspect the savings came from 2 sources: one is the use of electric on up/down hills, second from aerodynamics. The speed limit for most of the route was 65, so CC was set up to ~72. On Gen III MPG really goes down when you cross 75MPH threshold, YMMV

 

The battery helps, but it's not as good as momentum. You get better mileage by allowing speed to dissipate uphill and accumulate downhill without using the battery at all. Obviously this technique is limited by your patience and the amount of traffic on the road.

Tom

 

this is definitely the case for speeds under 45-50, but not at 70MHP+. Prius MPG takes serious hit at 75-80MPH, YMMV.

 

While I agree with your second sentence, I don't see the connection to the first or to the quoted snippet.

Does the battery storage become more efficient at higher speeds?
Does turning gravity into momentum work less efficiently at higher speeds?
Something else I am missing?