Getting maximum MPG on freeway

Not in the hills of Vermont it doesn't! The best I've seen (repeatable 400 mile round trip and above 50F temps) is 58 at 55 MPH (must have had a bit of a tail wind both ways). At 55 MPH, I can pretty much plan on 55 MPG, maybe 56 or 57 depending on wind. At 65 MPH, I figure at least 7 and sometimes as much as 10 MPH lower.

Just took the wife's '06 to Boston yesterday. 3 people on the way down (~500#) and 4 back (probably about 620#). The wife is a bit erratic on the accelerator and drove all the way down and about 1/3rd back. Speeds anywhere from 55 in the work areas to 78 (I'm pretty sure my '04 has NEVER seen 78 MPH). I use the cruise so the last ~150 miles were a steady 65. Total trip ~450 miles, 48.4 MPG.

 

Hi timwalsh,

JimboK is right. With the instrumentation in SHM, you see the battery current jump a little positive then negative, with less than 5 amps magnitude, sometimes only 2 or 3. The system is in esentially a zero current condition. This method is how to drive the Prius in the highest transmission ratio, with zero electric boost. This is why the SOC needs to be near 60 %. If its much less the car will charge the battery, if its much more the car will depleat the battery.

The advantage for me is about an extra 100 miles per 8.5 gallon tank of gas, over cruise-control.

You may have misunderstood my instructions. I am looking at the yellow instanteous fuel economy bar graph on the consumption screen. There are no yellow arrows on the energy screen while in SHM. Just the engine to wheels arrow, and a green arrow to the battery which flickers off and on, and rarely to yellow. The Prius display does not give any magnitudes of what it shows - this is one of the great ergonomic errors in the Prius dash-board design, which misleads the novice driver.

On a steep downhill, I will let the car drop into warp stealth (out of SHM) and then there were will be yellow arrows to the motor and from the motor to wheels. The speed accelerates during this time, on my highway route where this is done, up to about 56 maybe 58 mph (with a tail wind). At the base of the down hill, the car decelerates, and when I hit 53 mph, i lock in my pedal postion at 70 mpg again.

 

Ah, my mistake. I mixed up "SHM" and "warp stealth". I was thinking about "warp stealth."

I use that only for going downhill if the downhill would otherwise get my speed up too high. I treat it as the over-40-mph equivalent of gliding, since I don't ever want to take my foot completely off the pedal and go into regenerative braking.

I would not recommend something along the lines of "pulse and warp stealth."

Tim

 

Wow! That's a whopping 12MPG difference! Really? How come other posters say cruise control is good? I am confused. Could you please provide more data? Such as the MPG with cruse control vs. with your technique? And the speed at which the measurement was done. Thanks!

 

He describes using his techniques on hills, where CC is lousy as a fuel economy maximizer.

As I said earlier, I use CC only on terrain that is level or nearly so and when SHM is not feasible due to speed or traffic.

 

That is my opinion as well. I'm sorry if I didn't state it clear enough in my post. These meds have me on edge and short.

 

Hi 2009P...,

I might be optomistic estimating the SHM advantage. But, my highway commutes were never much better than the mid 50's mpgs with the cruise control at 58 mph. Versus 53 mph average in SHM, its not a fair comparison, but that is what that improvement is a comparison of.

Temperature has a big effect on SHM. So, this is a sumerime morning comparison (when I do my highway commute). If its above 65 F, and there is no heavy wind, one can hold the SHM, with a 70 mpg average up and down, on the small hills around here. The direction of my highway commute results in cross winds most of the time.

This week has been terrible for SHM, probably about 60 mpg average while on the highway. Temps have been from 47 to 53 F during those commutes, with head winds, and steady cross winds on all runs. I even had to come to screetch to a dead stop on one run, when a livery vehicle pulled out in front of me from the shoulder, while I was doing 45 mph due to traffic, about to go into the longest downhill (where I switch to warp stealth). He was picking up people from a car that stalled. He was also talking on a cell phone and did not even signal!

I have some aero mods on my car. The flush hubcaps I have measured a definate improvement with a coast down test. There are also upper A-pillar turbulators, which I know are pretty useless in any kinda cross wind, but in calm conditions might help a little based on tel-tale tests.

 

Is the basic premise for SHM the same? I.E. IGN14 TO IGN18?

I try to do this whenever I hit a back country road but the freeway would be dangerous to stay under 65mph around here which is why I just use CC.