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

I have noticed that I get better mpg driving at 60-65 mph than 55 -60 mph. Since I haven't driven a lot of highway miles and don't use cruise control or adjust for temperatures, I am wondering if other people had similar experience or did some more rigorous testing?

Yes absolutely.

It does appear that the Prius is set up or tuned to perform better at 60 mph.

No, absolutely not. Not in my Prius, nor my Subaru, nor in my prior Accord.

While I haven't carefully mapped my mpg vs. speed experience, it is in general agreement with the graph Bob Wilson has generated and repeatedly posted.

I get 5 MPG better at 55 MPH than what I get at 65 MPH.

While I respect the right of anyone to have any opinion they want to have, that is ludicrous! I suspect that if you were going slightly downhill at 65 as opposed to uphill at 55, it would be possible.

How could it possibly work that way? The ICE is working harder, at higher revolutions, and therefore using more fuel at 65 than at 55. Speed is not free.

Dream on.

ditto!

If you collect data more and more, you will see better mpg at 55 mph than 60 mph.

Ken@Japan

I seem to get the best at creeping, congested but slowly moving heavy traffic--slower the better as long as it isn't stop and go. The one upside to traffic congestion, I guess. Higher speeds do seem to drag it down.
~T

I know what you're saying Ken and I know you are very experienced in the workings of the Prius and I respect that, but I do find my Prius gets better mileage more easily at 60-65 mph than at 50-55 mph. I know there is more drag at higher speed etc etc but I find it much easier to get good mileage at about 62 mph.

Maybe it's one of those weird coincidence things but other members seem to have picked up on it also.

i along with most here, would advise that you continue to collect data on your mileage performance

lol is that a diplomatic way of saying I'm wrong?

Correct!

There is much data over the years suggesting Prius mileage declines in a pretty linear fashion with speed starting near 100mpg at 20 mph.

Not to say you ARE wrong, but you need to show test results that others can repeat in order to overcome a bias based on prior testing.

Look in the fuel economy threads for BobWilson4web posts, several of which include speed v mpg graphs.

Or could I put it another way? I'm not denying that the car is more efficient at 50 mph than 60, but that it is easier to achieve and maintain better mileage at 60 mph than 50. I find the car will happily sit at 60 mph and get good mileage. If I slow to 50 mph I find I'm always having to correct the speed and the fuel economy goes up and down etc.

Maybe if I really tried hard I would get better mileage at 50, but I do find that sitting at 60 mph I get a more consistant good mileage figure. Does this answer my (and obviously others too) findings better?

So your driving style at 50 is different than at 60. This change of style is a likely source of the discrepancy.

Definitely not me! Be it on a gen 2 or Gen 3 Prius, the 50-55 MPH range produces the better results for me... while anything above 55 results in a dramatic fall in FE. On this note, SHM above 55 is almost impossible on either car too.

Cheers

MSantos

Changing the speed leads to gaining and losing kinetic energy. Done as a bunch of small changes, especially if the speed loss is done with the car in "D", increases the total energy required and tends to put the engine into less efficient power modes. You are likely tossing energy into the battery and out, and this is better than a gas car but not the peak efficiency mode. Look for "regeneration" symbols ... the 'smoke' from inefficient driving.

In a perfect world, the regeneration drag of our Prius would be eliminated so when we let off on the gas, the car would automatically coast in "N" at least as far as MG1 and MG2 are concerned. It might have to run the ICE to maintain battery SOC but this would be a minor fuel cost.

Bob Wilson

i think we need to pay more attention to what we are doing at the different speeds. 60+mph roads are limited access, multi-lane, etc. lends for steady driving.

as others have suggested, the lack of changes in velocity is the reason you appear to get better mileage, but facts is, the slower you go, with all other factors even, the better your mileage will be PERIOD... that is the law, not a guideline. its simple physics. the amount of power needed to maintain a specific speed is not a constant. the faster you go, the more power u need to use for said distance traveled because of the increase in other forces that are working against that speed.

the other thing we need to look at is the efficiency of the engine and this is where Toyota is above all other hybrid manufacturers. this is why the Prius, despite being bigger, heavier and faster, still gets better gas mileage than its competitors.

but the most efficient speed is no where near 60 mph...its more like 37 mph...give or take a few...

so ya, u are wrong.

I am trying to collect data on what happens when I cruise at 60, 65, 70, 75. Thus far, faster means less mpg's almost without exception.
The "almost" probably relates to forced changes in speed (i.e., traffic) and hills.

I have not tested 55 and 50.

let me chime in by saying that on roads where speeds are 50 mph, in many cases, my mileage is the same or sometimes a bit lower than the freeway which generally drive at 60-63 mph. but again, that is because the 50 mph road i drive is single lane, does have traffic lights, albeit some are spaced 5 miles apart, but only having to stop for a SINGLE light is enough to destroy your average mileage for the next 10-20 miles (dont have specific data on that...obviously depends on how you stop and regain your crusing speed)

so, unless you are on a road with no traffic interruptions no more often than say 5-10 miles apart at 50 mph or so, u will most likely see a drop in your mileage.

I am not disputing that the general trend of lower speed = high mpg. However, there seems to be this area around 55 mph, there is a discontinuity. Here is my not so systematic observation, it seems that electric motor get more involved when driving at 55 mph than at 65 mph. That may explain the physics behind it.

Here is my theory:
Prius has two algorithm for maximizing MPG. One for the city driving and the other for the highway driving.
At city driving, electric motor get involved more because the electric charge it uses are more likely comes from regenerate braking (i.e. free energy). Thus you get better mpg. The same strategy doesn't work very well for highway, because we don't brake as much. Having electric motor get more involved just means energy get converted twice and the system get less efficient.

Without cruise control, system at some point has to decide which algorithm to use. My speculation is that this is done somewhere around 50-55 mph. That may explain the counter trend point at 55 mph. That is why they recommend you to use cruise control on the highway because that would tell prius to use highway algorithm.

My question is for generating mph to mpg chart, did people use cruise control? If so, that may explain the discrepency.

Just my 2 cents.