Getting maximum MPG on freeway

[alevinemi]

I've owned my Prius for about 3 weeks now, and I'm getting the hang of pulse & glide at city speeds (under 41MPH). I'm getting better at getting the Prius into the 'no arrows' state, and can usually average high-50 to low-60 MPG in the city. It's amazing how far that car can glide....

However, I have tried the 'stealth warp' or 'stealth glide' tactic on the freeway, and I just can't get it to stick. By the time I finally manage to get only yellow arrows to the wheels, I've lost so much speed I need to pulse again. Even when I get the yellow arrows, I can't hold them in that state well. There seems to be almost no margin for error. I end up pulsing too much, and over long distances, I can't beat cruise control's MPG.

Is there any other driving tricks to maximizing MPG on the freeway that are easier to implement? Assume that I want to average 60MPH or more. Right now, my best tactic is cruise, which gets me a little over 50MPG.

-->Adam

[yardman 49]

Hello Adam:

I've had my Prius for a couple of months now. I've only begun experiencing "stealth glide" (if that's what it's called) within the last few weeks. Actually, I wasn't even trying for it; it just started happening on its own.

Part of it was the mild weather we started having. But also I think that part of it has to do with the battery becoming better "conditioned". I read somewhere that it takes a while before a new battery can take a full charge.

There seems to be a correlation between the charge state of the traction battery and how readily the car will enter "stealth" or "warp" mode.

Also, it will happen more readily when the load on the car is very light, such as going down slight grades, no significant head wind, etc.

Best wishes,

[alevinemi]

The battery should be conditioned - this is a 'new to me' Prius. It's an '07 with 12000 miles on it. However, weight could be the problem.

If I am on the freeway, I am hauling (at minimum) my wife, two kids, a stroller, baby sundries, and a few snacks for when the baby needs them. And, unfortunately, neither I nor my wife are small. Total cargo/passenger weight is probably around 450 to 500 lbs, not including the spare tire.

I also noticed that cruise control will sometimes hit all yellow arrows on a downhill stretch.

For anyone not knowing what I'm talking about, the theory of warp stealth glide is here:

http://www.techno-fandom.org/~hobbit/cars/warpstealth.html

-->Adam

[GreenJuice]

Originally Posted by alevinemi

There seems to be almost no margin for error.

In case you haven't come across Hobbit's webpage on this, there is a graph which shows a relationship between this 'margin for error' which he calls a plateau, and the state of charge (SOC) of your HV battery. The higher the charge the greater your capability to hold these glides.

Alternatively, you might like to try out another technique called Super Highway Mode (SHM) which I think may be a little easier to hold. An essential difference in the glides between these techniques, is that for SHM the ICE is on at a low RPM kept just at the point where it flicks between charging and not charging the battery, whereas in warp stealth the RPM is dropped lower and the battery is assisting with the glide.

You will need to consider getting additional instrumentation to help you with these though (like CanView or ScanGauge II). They give you the confidence to hold a particular pedal position. Sometimes it takes just a few extra seconds to settle down into a perfect glide and see your iMPG soar! I realised after getting SGII that I must have been previously over-correcting my pedal adjustments because of the minimal delays in the updating of arrows on the MFD.

Edit: Oops! I see you've just posted the same link. We must've been typing at the same time!

[GreenJuice]

Originally Posted by yardman 49

I've had my Prius for a couple of months now

Congratulations to both you and Adam for exploring these techniques so soon after getting your cars. I think its a real tribute to the many masters who contribute to this fantastic website!

[alevinemi]

Thanks!

SHM looks intriguing, but I don't have a ScanGuage or a Tachometer to try to figure out if I'm in the sweet spot. Given that I tapped myself out for the down payment, I'm not up on buying/installing modifications at this time. The ScanGuage is over $100, and from the looks of it, my wife would think it was ugly. Fortunately, it looks easy to install.

I'll try to do SHM by engine noise, but my Prius is pretty quiet - it will be very tough. From the way I understand, you should pulse, then go to a low RPM state (roughly 1200 RPM, which is pretty low). The car will slowly decelerate, then pulse again.

-->Adam

[9G-man]

Originally Posted by alevinemi

I've owned my Prius for about 3 weeks now, and I'm getting the hang of pulse & glide at city speeds (under 41MPH). I'm getting better at getting the Prius into the 'no arrows' state, and can usually average high-50 to low-60 MPG in the city. It's amazing how far that car can glide....

However, I have tried the 'stealth warp' or 'stealth glide' tactic on the freeway, and I just can't get it to stick. By the time I finally manage to get only yellow arrows to the wheels, I've lost so much speed I need to pulse again. Even when I get the yellow arrows, I can't hold them in that state well. There seems to be almost no margin for error. I end up pulsing too much, and over long distances, I can't beat cruise control's MPG.

Is there any other driving tricks to maximizing MPG on the freeway that are easier to implement? Assume that I want to average 60MPH or more. Right now, my best tactic is cruise, which gets me a little over 50MPG.

-->Adam

Good job, your gas mileage shows you understand how to take advantage of how the Prius works and you are trying to maximize the amount of time the ICE off. That's something every Prius owner should be doing.
To answer your question about freeway MPG improvement.....simply slowing down seems to have the greatest positive impact on MPG.
60MPH = 60 MPG+ in a Prius.
Beyond that, Take advantage of hills and intentionally go into a warp stealth on the downhills. Hold it until your speeds begins to bleed off.
I can maintain 60 MPH in a warp stealth on downhills regularly here in GA.
Every hill is an opportunity to exploit this car.
Every hill I crest, the right foot comes off the gas pedal and I lightly reapply to get the warp steath or glide.
Cruise control is remarkably adept at doing all this too.

[ETP]

OK, my list>

My Honda has a RPM gage, better seats, better navigation. Everythingelse so far my Prius kicks ###.
So any way to do this without adding a scan gage? I think my wife will say no to that for sure.

[ETP]

OK, I read most of the link but how does this work at 65-70 MPH if at all?

[JimboK]

SHM also is dependent on optimal SOC, around 60% (6 blue bars). It is indeed executed at a low RPM, and I agree that it is much easier with added instrumentation -- though it's still not simple or intuitive. Lacking the instruments, you can try to hit it by gradually easing off the go-pedal until just before the ICE shuts down (watch the Energy monitor), with trial-and-error likely needed before getting a good sense of that threshold.

I find SHM's usefulness rather limited on the typical terrain in my neck of the woods. It seems to work best on level terrain where gradual slowing (into 40-45 MPH territory) doesn't impede traffic or cause a safety issue. I-95 through central VA, for example, doesn't meet those criteria! Instead, I generally use a combination of warp stealth (on hills) and a slightly higher RPM to maintain a steady speed (on the flat). If traffic is light enough and the hills aren't too steep, I'll keep the RPM steady on the hills too, losing speed on the uphill and gaining it going down.

In any situation, city or highway, I seek routes favorable for high-efficiency driving.

Originally Posted by ETP

OK, I read most of the link but how does this work at 65-70 MPH if at all?

Which link?

SHM is rather impractical at those speeds. Warp stealth is quite possible, more practical on hills.