Better mpg at 60-65 mph than at 55 - 60 mph

Sorry, but that is goobledygook. It is not a trend. It is a simple matter of scientific fact. Unless you are talking about a truck which is geared for a particular speed, and is lugging at a lower speed, it just does not happen that a higher speed lowers the mpg.

BUT, whatever turns you on!

 

Since I've never had my 2010 Prius over 60 mph I can't tell what the mileage is above that speed. I get better highway mileage at 50 mph than 55 mph. I get better gas mileage at 55 mph than I get at 60 mph.

I have seen what your talking about in older Volvo's from the eighties. There was almost no difference between 55 mph and 60-62 mph in fuel mileage. Anything over 65 mph you would see a real dump in fuel mileage. This BTW only applied to automatic transmission cars. The best speed to drive these automatic transmissioned cars on the highway was always around 100 Km per hour. Manual transmissioned cars on the other hand always saw their best mileage in the 45-55 mph range.

 

I will throw my 2 cents in. I now have 37,000 on my 2009 and have tried all different driving styles to get the best mileage I can.

I have never gotten better gas mileage at 60 then I did at 55.

And I have never gotten better gas mileage with the cruise control on then with it off.

But I would love to hear how to get better mileage in either of those circumstances.

 

Aerodynamic drag goes up by the square of the speed. If you drive twice as fast, it takes four times the energy and eight times the power. That part is scientific fact.

Cruise Control does not change the basic "algorithm" of the Prius controller. We know this from conversations with the Prius engineering staff.

Best cruise efficiency from the HSD comes when all of the power goes mechanically from the ICE to the drive wheels. Power directed through the MGs is less efficient, and power extracted from the battery is a *lot* less efficient. Because of the variable nature of the HSD, direct drive (as direct as it can be) can occur at a variety of speeds. At lower speeds it is not practical, as the ICE would lug.

Because of the Atkinson Cycle ICE, pumping losses tend to be lower with the Prius ICE. This makes the Prius ICE less speed sensitive, although it does not have good low end torque.

The Prius HSD does a pretty good job keeping the ICE running at an efficient setting. I wouldn't expect to see much efficiency difference between 55 and 65 mph. I would expect the differences in aerodynamic drag to be much larger than any HSD efficiency factors at those speeds.

Tom

 

They only way one could get a better mileage at 65 MPH rather than 55 MPH is if he drives alone on a 55 MPH road and drive behind a trailer truck or very near another car on a 65 MPH road to reduce drag. In heavy traffic at 65 MPH, this could happen...

 

...or if:

1) The 55 mph road is uphill;

2) The 55 mph road has a higher drag surface;

3) The 55 mph road has many curves;

4) The 55 mph road requires frequent speed changes;

5) It is always cold when he drives the 55 mph road;

6) Or any of a number of other factors.

Tom

 

Going to work I get about 56 on a nice day. Going home I do alot better. Here are some pics. The trip is about 36.9 miles and I drive about 61 MPH.











I live in Ohio were the roads are flat. There must be some small decline on the way home.

 

that or diff in temps, prevailing winds, etc. i have same issue. my commute to work runs about 50-51 mpg at this time of year (MFD readings) but on way home its 55-58.

but morning commute in the dark (even this far north, i can only drive without lights about a week or so.) and usually colder. also, morning commute, no traffic to speak of, afternoon trip is bumper to bumper for nearly 50 % of the distance.

 

If the ICE rpm is 1963 rpm at 60 mph, it is the zero MG1 rpm condition.
http://priuschat.com/forums/gen-iii...-gen-prius-what-do-we-know-2.html#post1047339
However, the 1963 rpm power is far exceeded for 60 mph flat road cruising.

Ken@Japan

 

Plus, going 10% percent faster creates like 20% greater drag.

 

I'm definitely trying to convince you that the earth is flat here arn't I?

Perhaps we are wrong but the impression that I and it appears, many others have is that the car 'appears' to get better fuel economy at 60 than at 50 mph. I accept that 50 mph IS a more efficient speed (proven so) but I find my car gets a better OVERALL fuel economy in an EASIER way at 60 mph. It also appears that others do too.

 

Traffic engineers have been working for decades to improve roads and traffic flows. In some areas, there will be an optimum road speed that is different from the performance achieved by the vehicle on an closed or limited traffic road. For example, when I travel down Holmes Ave through downtown Huntsville, a speed of exactly 24 mph works perfectly as the lights are synchronized for that speed. I am constantly amused at drivers to bust the speed limit only to come to a complete stop at each light.

Vehicle performance is one element but it has to be matched to the driving conditions. Terrain driving means matching the vehicle to rises and depressions to optimize fuel consumption and it pays dividends. So I'm not surprised that depending upon the local roads, there may be optimum routes and speeds:

For example, our NHW11 performance is improved by taking a route through the neighborhood at 25 mph to minimize power draw when the engine is cold and relatively inefficient. Mileage is also improved by taking the Governor's drive short-cut even though there are more lights and I usually have to come to at least one complete stop. Yet overall mileage is much improved over the higher speed and longer distances of the cross town routes.

Tuning the route including speeds to match the vehicle performance is my trick for efficient driving.

Bob Wilson

 

Now that is possible. And I would not want to give the impression that I drive at 50 on a regular basis. My time still has some value to me and I regularly blow the MPG for MPH, but I do not think it is anything but a compromise.

 

Grumpy, do you have any data where you have tested the same route at the same temp and winds, round trip or same direction at steady state 50 and 60, no traffic or stops interfering?

 

Certainly, I take the interstate at 60 or even higher mph, instead of back roads where I can pulse & glide and slow down, because the little towns make me stop and the grades on the roads are much worse (the interstates have bigger grades than railroad tracks, but much more like that than the back roads that just lay asphalt over existing terrain).

Unless I slow WAY down, the steady state and reduced climbing of the higher speed route give as good or better mpg, easier, as you say, and faster. But for me it is NOT because 55 is higher FE than 65 or whatever.

 

Nope, just my gut feeling - and you can't get more scientific than that

 

My 2010 Prius seems to have a 'sweet spot' at 53 mph. It will maintain 53 mph at a constant throttle position better than speeds above and below 53 mph. I don't have any data to support this and it might even be a problem with the speed indicator(53 mph display might have a range of 1.5 mph instead of 1 mph). Does anyone else have a similar experience?