Highway driving, better MPG with or without cruise control?

Conventional wisdom is that you'll get better mileage avoiding the cruise control if you're encountering hills. Your advantage is that you can see the upcoming hills and (traffic permitting) build up a little speed approaching and let it bleed off as you ascend. I will use cruise control for dead flat terrain.
Best speed for mpg is probably around 30 mph of you can pulse and glide. On the highway 50 is better than 60 which is better than 70 because of the work pushing the air around.

 

Cruise control off is better for mileage if you pay attention if you don't your better off with CC on. CC is much nicer to other drivers and I usually use it on highways when there is traffic. On open highways with higher speed limits I usually set the CC for 2 or 3 MPH over the speed limit to compensate for speedometer error, that seems to keep me at the same speed as most of the other cars.

 

On my 80-mile weekday round trip here in the flat part of North Carolina, I set the cruise on 55 (limit is 55 and 60), stay in the right lane and get about 62 mpg in summer (low 50's in winter). A lot of people pass me, but I don't cause a traffic jam.

 

Best MPG is actually similar to most cars, 45-55 MPH.

Building up speed for a hill doesn't save fuel. Coasting over the top letting the speed drop as you approach the top is what helps mileage. Cruise doesn't do that.

Other than that, running on cruise is not noticeably different from using the pedal manually, mileage wise. At least that's what I see.

The Prius engine is most efficient at about 80% full throttle. So near full throttle is actually good, provided you can then coast for awhile.

 

Here is Bob's famous chart. It's fairly accurate given the variable nature of driving conditions.


For me, the difference between driving 80mph (40mpg) vs. 65mph (55mpg) would cost me over $700 annually (30,000 miles / mpg * $3.8). No one else is paying for my fuel so if they don't like me driving the speed limit then F' them.

 

Aye. I've been driving a Prius since 2005 and excluding severe conditions, the graph is pretty accurate. On my long trips to LA I generally try to maintain 80-85mph as much as possible. Average displayed speed is usually in the 70mph range and mpg is around 42mpg or so and that was with great tires.

High speed kills mpg.

 

Ohh no. It does. I've tested it over and over again. 3mpg minimum loss unless you are using the OE 17" tires. 6+mpg loss if you are using something more performance oriented. lol

 

F8L your 12 prius was clean in person.


Normally the cruise drops my economy.

But my best trip from Auburn to Rocklin 10 ish miles downhill I made my best trip at 100mpg with cruise on.

 

I prefer cruise control when doing interstate driving. More so with the Prius. I find it difficult to maintain a constant speed without it. I like, "steady as she goes"...

 

Last month I was able to cross Nevada in my winter gas guzzler without going over 65 mph. When cars overtake at an average rate of just one every five to ten minutes, there is really no pressure to maintain any particular speed. And between speed limiters and fuel prices, most commercial trucks were sticking to similar speeds.

As the earlier graph shows, Prius' best MPG is at the slowest speed you can otherwise tolerate, down to about 15-20 mph.

 

Thanks! Makes me sad that it's gone though. Someone is probably cruising it around Auburn now.

 

I don't see better mileage at speeds lower than 60 km/hr (around 40 MPH), rather I see worse mileage. But I've never been able to maintain motion at 50 km/hr for very long due to lights and traffic. I've always thought the reason the mileage I see drops at speeds below 60 km/hr was because of "parasitic losses". Systems running using power but not providing motive power to the wheels.
I see the best mileage around 70 km/hr, on cruise or not. And good mileage at 80 km/hr even on very wicked mountain roads.

So I guess I disagree with the posted graph.

 

I believe it is meant to illustrate steady state mpg over time. During short distance cruising at low speeds <45mph, the engine may cycle on and off. At times this will put you in EV mode and you'll see "infinite mpg" but when the ICE fires back up to recharge the HV battery, your mpg will drop into the 40s or 50s?. Over time, however, your average would be something over 80mpg. While doing my pulse & glide marathon I was able to get 109mpg with a 35mph average speed for 2+hours.

 

Got 78.1 MPG driving on LA freeway..Half of it was cruising.