Red, until you pick up WB's simulator, I thought you may be interested in a few numbers ..

No wind, no AC, sea level, summer petrol.

mph .. mpg
61 ... 60.78
64 ... 58.11
68 ... 54.75
71 ... 52.36
76 ... 48.65

My nmeumonic that I remember is that the Prius is part of the 60/60 club

Oops, I just saw that I had the Cd at 0.25 rather than 0.26. The mpg's are off by one mpg or so .. Sorry

 

What I'm saying though is I've driven 65 and gotten worse mileage. That's why I decided to speed up and I ended up getting better (??) going slower is fine, but I just end up getting everyone mad at me, especially on the two lane highway I drive. I don't mind driving slower and I do so when I can afford the time. My point in starting this thread was to see if there was somehow a speed that would magically help everyone increase mileage, apparently not, though. I'm not getting hostile or anything, it just seems like you're throwing out programs and stuff that simulate this and that when I'm telling you I've actually bettered my mileage with increased speed.

 

I would guess that there are other infuences that may have gone unnoticed, e.g., elevation decline or wind shift (or driving direction). There are times when my mileage shoots up (or down) and I don't know why - usually it's elevation changing. And you can't see it. You have to use the NAVI or GPS to tell.

If you get out on, say, a 5 mile stretch of road and try different speeds repeating the same stretch in the same direction, it will probably be the best simulation you can get without running something like the WB simulator program.

 

What Tink says

Wind in particular has an *enormous* influence, and is probably the culprit in day to day variations that are seen.

E.g., a 5 mph tailwind driving 69 mph will increase your mpg from 64.78 to 70.53 ! I think the change approximates car speed in the opposite direction, but really have not played around with the simulator enough to be sure. So if you drive into a 10 mph wind at 50, your mpg will approximate driving 60 mph without any wind.

New Mexico gets pretty windy, so I have taken to looking at the weather report to try and time my trips. I know -- that is rather extreme -- but it makes quite a difference.

 

Correct. You may do great at 70 mph, but you'll do really great at 50 mph.

 

Ok - I'm jumping in a little late here, and I know there's been a bunch of viewpoints refuting Red's answer...but I'm going to join him in this debate - to the extent that I notice certain speeds returning greater values on the instantaneous - and that speed is at 8 mph within each 10mph range.

To wit - 38 / 48 / 58 / 68

I'm not going to say that I get better mileage at 68 vs 48 - indeed, 48 is about the sweetest spot for me - I can now peg the instantaneous at 80mph for a couple of minutes or more on level ground, and hold 70 with some ease when I'm around that speed. This is dependent on temperature. So, in this respect, I'll join Lakedude - in my suburban loop, I'll keep between 42 and 48, depending on traffic. And that's my best, per the FCD (I know, it's not called that in the Honda, but it's so much easier than typing 'instantaneous' all day The only problem is that I can't sustain a steady speed in suburban driving, and I won't travel 48mph on the interstate. So I'm limited to see if the mileage actually proves true to the FCD, were I to travel long enough at that speed, largely unimpeded.

Where this largely comes into play for me, is that I find it *easier* to hold a steady speed while still dropping back on the throttle for that extra 20%, at those points on the speedo. The lower end of each 10mph range, I tend to lose speed on level ground when I ease up on the throttle to load the engine efficiently, and if I don't correct it, wind up eventually dropping down to the next lower gear (42mph is where 5th gear kicks in on the AH, and TC lockup occurs at 48mph or so). That's why I think 45-48 is the optimum speed (for me at least) - the driveline of the AH is optimized at that speed, and speed in excess of that, produces diminishing returns.

I remember when I drove to Madison w/ Xcel, and I told him that it was easier for me to hold 48 than 42, et al. I don't think he agreed with me, but he didn't argue the point, and I thought that maybe I *was* imagining things. But then I saw this thread. And I'm here to say that I think there's something to this. Can I back up my hypothesis w/ science or engineering? Not yet. But I've got 4 months and 7500 miles of experience behind me at this point

All that said, I find myself these days pretty much maintaing the limit or even a little under, and I find it almost impossible to accellerate from 40 to 50, for example, before my next stop light, etc makes me slow down. The nice thing is that now, I almost never take the car out of VCM while accellerating any more (Xcel noticed how easily VCM could be deactivated when he drove the car).

 

Thanks for somewhat backing me up. I understand that slower is better, but in that case why don't I get like a billion miles to the gallon when I'm driving 15 miles per hour?

 

Well, your Prius is optimized for 35-40 MPG, so you can start by going 35-40 instead of 15 But, in all seriousness, you can't get a billion miles to the gallon for a couple reasons: current technology is far too inefficient to harvest all of the energy, and there isn't enough energy in gasoline to get you there, even at 100% efficiency.

 

Hi Red_The_Impaler:

___You are if your Prius II is in stealth mode which is where it should be. You will pay for it later with the recharge however

___The reason 33 - 35 mph on a relatively flat and windless road in a Prius II or Insight 5-speed work so well is that they are at a minimum RPM and power to keep the car from decelerating and maximum gear ratio to keep the RPM’s at their minimum. You would be surprised to see the heat losses of a gear train as RPM’s rise … At 15 mph, you are probably not pushing the highest ratio and the ICE would be lugging severely if it was.

___Good Luck

___Wayne R. Gerdes
___Waynegerdes@earthlink.net

 

I can say that I have never been able to achieve 70 MPG unless my speed was below 55 MPH. But that doesn't mean that it can't be done. Two things that could have contributed to your 73 MPG was a tail wind and/or a decrease in elevation.

I have done a lot of testing at different speeds and have developed a speed vs MPG curve for MY car. Under optimal conditions, warm temps, no air conditioning, no significant winds:
- 70MPH = 50MPG
- 65MPH = 55MPG
- 60MPH = 60MPG
- 55MPH = 65MPG
- 50MPH = 70MPG
- 45MPH = 75MPG
- 40MPH = 80MPG
- 35MPH = 85MPG

The most important thing is to only consider round trips. That way you can rule out a change in elevation. I also carry an altimeter on board which reports elevation in increments of 5 ft. Watching the altimeter is an eye opening experience. When I thought I was climbing, I was actually flat or falling, and vice versa. I now rely on the altimeter instead of my instincts.