I've been wondering if there is a magic number for getting the most mileage out of your car? Out here the speed limit is 65 on the freeway, if I drive 65 and put the car on cruise control I get something like 46mpg, but if I slow to 63 I bump up my mpg, but **** off the people behind me, at 68 I get varying results, but mostly 50-60 miles per gallon. So, I've determined, very unscientifically mind you, that 68 is a good speed to drive. What I'm trying to figure out is what speeds help to maximize FE while maintaining freeway speed. Since in the city, between 30-40 you can get the electric motor to take over at any time given you have enough battery. The reason I ask is because I see many Priuses driving by at speeds I'd estimate at 70-80 miles per hour. I've driven 70-75 and seen various results, some including 73mpg, so I wonder if they know something I don't. Does this make sense? Here's what you should do if you want to help.

*Your make, model and year (I know it's probably in your profile, but humor me)
*The legal speed limit in your area
*Passenger's Yes/No. Any load whatsoever?
*Your "magic" number

In my case it's:
*2005 Toyota Prius
*65 mph
*no passengers car is basically empty
*68 until I find another

In theory, I would guess that under ideal conditions this would give everyone the same ability to get the most FE out of their car, while maybe even learning something they didn't know about it.

 

I travel in the far right lane, and venture to the next left lane if the right one clogs up.

If the divided freeway has only two traveling lanes:
70MPH limit I'll go 65-68 with traffic, if there's nobody behind it will sag to lower 60's.
65MPH limit I'll go 62-65, same traffic rules as above.
55MPH limint is 55-62, same traffic rules.

Mind you I'll go faster in the valleys and low areas than at the top of hills.
If there is less traffic I'll let it sag more ove the hill tops.

I avoid +65MPH unless neccessary.

 

Aerodynamic resistance is proportional to the **square** of the velocity. At speeds under 35 or so, other factors come into play, but above 35 it is effectively all about wind resistance. Simply, as Hot_Georgia says, slow down as much as you can on the highway.

I strongly recommend you track down Wayne Brown's Palm program that simulates Prius II mpg under different driving conditions. If you do not own a palm pilot, OS simulators for windows and Macintosh exist. It is a *real* eye opener.

 

Wayne, among others, have shown that the ideal speeds on the Toyota Prius II are between 35-40 MPH. The faster you go than that, the worse your mileage. The slower, the worse as well.

 

Ideal while you have battery charge, though, right? Once you reach a certain point, you've got no battery and therefore you join the "common" cars with above average gas mileage. What I mean is that I can drive 68 and average 50-60 mpg by the computer's reasoning. That's a good number considering that a lot of people here can't hit it. I have been keeping tabs on my tanks since I discovered this site, and while I don't have my signature posted here, I do have it on another site where at this moment I am sitting at a nice 52.xx mpg. You can see my stats listed under the Silver Millenium Falcon. Nearly my entire drive is freeway and while I'm still learning to drive the car with the utmost FE in mind I'd say my numbers are pretty good.

 

I seriously doubt anyone with a Prius is getting 73mpg at speeds over 70mph unless it is down hill or with the wind. Jason is correct in saying that the ideal speed for mileage is much slower, around 40mph. Of course traffic forces a compromize. Personally I tend to drive around 45mph most of the time.

 

Red,
I'm not sure what you mean. At optimum speed, the Prius trades between engine on and off. When it's on, it sometimes replenishes the battery. Yet, <40mph is slow enough that the motor can solely propel the automobile.

 

It is the wind resistance that makes the speed ideal not the charge in the packs. As has already been said if you go too slow you are not in top gear so you lose mpgs. If you go much faster wind resistance goes up and once again you lose mpgs. Wind resistance goes up with the square of speed so it takes twice as much power to push a car 70 as it does 50.

 

So, what you're saying is that when I drove in to work today at ~70 mph (I was running late) and actually increased my MPG for the straight, flat land that you can't drive fast and still maintain good FE? If that's true then one of the following must also be true: a. my car is different from yours b. my computer is malfunctioning c. I'm a liar
I'm just telling you what I see, obviously the car doesn't maintain a steady 70 MPG at 73 MPH, for long stretches, that wasn't my point I've seen it for minutes at a time, it's not just a momentary thing. At 68 the car will on straight, flat land the car will get me over 50 MPG it will dip into the 40's occasionally, but it goes right back up and maintains it for miles at a time. I wish I could prove it to you, but short of video nothing would do so. I do notice though that when I get that mileage that the electric motor is very frequently pitching in, never dipping below the third bar, and also mind you that this is with cruise control on and I never get traffic.

 

I don't believe he was saying a, b, or c. I believe he was saying that you would have gotten even better at a lower speed.

If that's not correct, Lakedude, feel free to correct me.

Friendly & contructive - that's our motto.... Not really, but it could be.