Speeds to avoid?

Assuming steady speeds, the Prius' fuel economy decreases more or less linearly with speed above 20 MPH. The only blip in that line is at 40-41 MPH, below which the car will run on electric only, but not above. So you'll do better by staying at or below 40, assuming traffic and your own tolerance for driving below the speed limit allow. See this for more.

 

Hi All,

I agree with JimboK, but be aware that these graphs do not have the impact of a newly realized operational method called Super Highway Mode. With SHM, temps between 65 and 85, no wind and a level road without stops, one should be able to get near 70 mpg at 53 mph, and 1280 RPM, after a battery charge-up to 60 % SOC. This is a steady state engine driven mode. I guess this is the capability of the Atkinson engine to run at low powers efficiently, and the wide gearing range of the ECVT to match the engine when its running that slow while the car is relatively fast that is responsible for this.

Below about 48 mph, engine speed becomes too slow at a steady RPM for it to operate efficiently in SHM, and the car has to switch back and forth between battery, battery assisted egnine and engine powered. When in pure battery mode, the car is wasting energy to keep the engine turning, but unfired above 41 mph.

Below 40 mph, pulse and glide works great yielding similar to better mileage than SHM, depending on stops and traffic going at the wrong speed at the wrong portion of the cycle.

 

I try to avoid speeds greater than 10% over the posted limit. Most of the time.

 

It feels less efficient/like it is loafing/lugging and shouldn't even be on from 42 until ~50. I try to stay out of that band as I've gotten much better indicated gas mileage above and below.

 

88 miles per hour. You wouldn't want those 1.21 jiggawatt-hours to get used up.

 

767.58 mph

Damn Noise Ordinances

KK6PD

 

Remain below the speed of light. There are, however distinct advantages and disadvantages when traveling at light speed:

Advantage 1: Whenever you approach a red traffic light, it always appears green.
Advantage 2: You can't see a police car's red light in your mirror.
Disadvantage 1: Flashing your high beams at a car in front does no good.
Disadvantage 2: You can't see the reflectors in the road.

 

I suspect you could also achieve maximum mass to energy transfer and vice versa. Or something like that.

 

Low Speeds:
My experience is that the best efficiency is at roads at with moderate uphills that allow sufficient pedal pressure to maintain speeds between 20-30 mph followed by very modest downhills that allow gliding for as long as possible. Back when I cared about efficiency I wouldn't turn on the heating. During winter-time that made a huge difference in the city: without heating at 72F I would get about 45-50 mpg with heating it has come down between 35-40 mpg. Thankfully I mostly drive highway now; A/C does not have such a huge impact there.

High Speeds:
Due to my Greek upbringing and the lack of patience that confers, I have succumbed to traveling with cruise control at around 68 mph. Back in the days that I cared about efficiency I had found that 52-57 mph with cruise control and AC at 72F at summertime would easily get me ~55 mpg.

My OEM tires are always at 44 psi following the great recommendations of people here and they look like they have really good tread left in them

 

It's not just a good idea, its the law.

 

Not only it's the law, you have to always travel at lower speed to avoid being 'Late' to your destination (due to time-dilation)...

 

The "41 to 46" mph range is the speed difference between the Prius and new Ford Fusion EV modes. For the NHW11 and NHW20 Prius, the threshold speed is 42 mph. Below 42 mph, you can run EV, at and above, the engine has to run all of the time.

Early on, I performed and captured every MPG vs MPH data I could generate or find. These charts show what I've found:

In this chart, I have two NHW20 MPG vs. MPH charts at highway speeds. You'll notice there is a dip around 85-90 mph. This corresponds with the speed zone where the engine has to run to keep MG1 spinning slower than 10,000 rpm. The NHW11 has a dip at ~70 mph that corresponds with keeping its earlier generation, MG1 slower than 6,000 rpm.

This next chart includes the drag vs MPG curve for an NHW11 Prius along with some data points from the original NHW20 marathon (the black dots.) The Prius marathon was run in August, significantly warmer than a standard day:


This second chart also includes at 34 mph my results of testing 'pulse and glide' with my NHW11 versus cruise control, equivalent speed.

My data records indicate there are significant savings from:

• not overfilled engine oil
• warmer weather or a 'hack' to trick the engine into thinking it is warm

I have yet to do a tire pressure and alignment sensitivity test. So far, the literature universally recommends higher pressures. Tire wear recommends perfect alignment.

GOOD LUCK!
Bob Wilson