Most fuel efficient speed (highest MPG)?

There was a graph somewhere about this. If I remember correctly I think the MPG peaked at around 35MPH. I think the MPG was around 80-90MPG at that speed. Maybe some one here has that graph.

 

I think I was wrong unless this is not the right graph. I just remembered the speed was pretty slow and the MPG was pretty high.

http://priuschat.com/forums/fuel-economy/14675-most-efficient-speed-best-mpg-2.html#post385271

 

So it looks like the peak is around 20 mph or even 25 mph depending on one's interpretation of the temp. effect in the data. From a little over 15 mph through 30 mph it is 100+ mpg with OEM tires at stock pressures.

 

Questions?

Bob Wilson

 

Hi '09Prius,

A 35/41 mph pulse and glide is good for the high 70's mpg. 53 mph on the level highway with no wind in super highway mode is good for the low 70's mpg.

If traffic would allow, a 20/41 mpg pulse and glide would probably up near 100 mpg.

 

I don't understand how you get these numbers. I consider myself pretty learned on P+G as well as other things such as slowing to a stop light to catch it on Green etc. The best I can ever acheive over say a 15 min stretch is about 65mpg. My lifetime avg is around 55 and my current tank is averaging 60mpg. I live in an area where it is relatively cool, however, last couple weeks been realy warm mid 80's to lower 90's. How do you acheive such high mpg's? Is it because you live in a completely flat state? Massachusetts is far from that.

Also, my commute is about 1 hour a day through rolling hills.

 

It's not just you, I accelerate slowly, drive the speed limit, keep my tires inflated, keep the windows rolled up and AC off (as much as possible) - and while I get good mileage, I never see the high numbers others post. My Prius mileage averages about 47. I don't understand how they do it...

 

They drive 10-15 mph below speed limit. 15 @ 25mph, 30 @ 45mph, 50 @65mph.

 

Tom, it takes practice and patience. I'm still refining my technique after 3.5 years.

If you're anywhere near Boston, you might consider contacting PC member Hobbit for a hands-on clinic.

 

It's infrequent that I get conditions favorable to the speeds mentioned, but when it happens extended runs at 70 mpg are indeed possible, even for a novice in P&G. Since I almost never get true P&G terrain around here for more than a mile it is amazing to me what the car is capable of. I hadn't had the car long when I was half way through a tank with 67 mpg showing...and I was running around the speed limit.

Current tank is running 53.6, which I maintained today with no loss on two 2.2 mile legs several hours apart over hills, curves, and half a dozen stops each way.

 

Hi Tom,

Most likely the differnce is the hills for SHM. My highway driving has a long stretch of level straight roadway where there are many times no cars in front or behind me. I can concentrate on the pedal adjustment there, and in the consumption screen using the instantaeous gauge I adjust for 70 mpg, and this will hold the 53 mph. If its warm, and there is a tail wind, I will adjust for 75 mpg and the car will still hold 53 mph during that portion. In some conditions with the holding the 70 mpg gas pedal position, the car will get up to 56 mph in short order. Then I lift off to get back to 53 mph and will be in high 70's. Other conditions, at 70 mpg consumption the car just rolls along at 51 mph - due to cold tires, cold dense air, or a headwind. This is with a fully warmed up car and with the SOC above 60%. Its critical for the SOC to be near the nominal that the hybrid system wants, or the car will not use the generator to charge the battery. When I first get on the highway with a 50 something SOC, I could see the car chaging the battery at about 20 amps at a steady speed. What the SHM mode is , is the base level of the vehicles fuel economy at that speed, without any electric load at all. When I was running the Mycanscan I could see the battery current down under an absolute value of 5 amps or less, sometimes charging, sometimes discharging.

Oddly, even at cold temps there are SHM regimes, but we usually do not see them in everyday driving because the tires are so cold. On some weekend trips last winter in 15 degree F bright sunny (had to be sunny) weather there was a nice SHM about 56 mph and 70+ mpg , but only after an hour of driving when the tires have warmed up. The cold air probably improves the engine volumetric efficiency, resulting in higher combustion temps, and better efficiency. In pulse and glide in this weather the mileage was much worse, most likely because the tires were cooling off.

The P+G mileage above is just for the P+G portion - not considering stopping. I have a 3 mile long, 5 minute portion of my drive that I do the 41/35 P+G on and so I can see the bar after that. I have also been on that portion of road just after refueling. Many times just after refueling my tank fuel economy is in the high 70's, thanks to the practice I do on the way from gas station home, and its down hill. So the next day the mileage is still effected by that. So on that P+G road section, I look at the mileage at the end of each glide. Even though each P+G is only about 1/2 mile, the mileage for the tank is going up. 73 mpg .... 73.2 mpg ..... 73.4 mpg .... So, I know that the mileage of the P+G mode is up above 73 mpg, probably in the high 70's.

The Pulse RPM is critical to good P+G mileage. I used to shoot for 2000 RPM when I had insturmentation. Now, I am just guessing about where that 2000 RPM is by the battery usage. Initially there will be battery usuage as you press the accellerator. But then it will drop out after a couple of seconds if your on the right pedal depression and the car will accellerate with no battery being used. You want to be just short of the battery being used to be using the engine at its efficient level. Too little pedal and the power will be too low for efficiency. This accelleration rate is very nominal compared to other cars. Not granny level, in fact one can have a problem with slow cars doing this. I just drop into electric until I get enough of a gap to accellerate efficiently. And its not a WOT burst either. The Mycanscan color keyed tachometer was the ideal way to learn this.

My tank economy is at 66.5 mpg right now. I usually do not get back to that average mileage till the last half of my commute. The last half of the commute routes have good gliding opportunities. Its not uncommon on one route to have 1/2 hour of 70-75-70-75, then a 50, and then a 100 as I approach my destination. The 50 and 100 is the up/down hill portion of the route.

 

I am not a fast driver, don't approach the limits much and haven't gotten to 50 mpg yet for a tank. Sure, on some 5-10 min segments I have seen that 100 but not overall tank.

 

The DVD which comes with the 2010 Manual shows how they feel you will get the best mileage using the Dashboard Display. Don't know if it's really on the mark but it makes sense.

 

I commute from San Diego to Orange County everyday (100 miles each way). Regardless of the speed 55mph / 65mph / 75~80mph I get 49.5MPG on average. Is the computer accurate? It is hard for me to know the true performance since the gas tank bladder is dynamic in volume size. My fill up today at 387 miles at 7.4 GAL while the computer showed 49.7MPG.

 

My best mileage is P&G between 22 and 27 MPH. On relatively flat terrain this will yield over 100 MPG consistently.

 

The chart talks about the hack...is this the engine temp. resistor added ...if not ,what then.....thanks

 

Hi Best...,

I have to give that a try.

My experience with such low speed P+G's is that I cannot get the car to kill the engine. If the engine stays on during the glide, I am lucky to get 55 mpg. If the top speed is above 35 mph the engine will kill, but not always, depending on the warme up / thermos bottle recharge cycles in the car. In fact, I cannot be confident it will kill the engine below 35 mph until I am 1/2 mile from the destination. I cannot be sure the car will kill the engine for a glide above 35 mph, until I am about 10 miles into a route when the temp is 60 or warmer. This became very apparent with the MYCANSCAN, as the tachometer would stay green rather than go black, when the glide attempt was made.

Are you using the EV switch to kill the engine after pulsing ? Are you using the temperature sensor hack ?

 

Yep, this is what I observe as well. I go ahead and take it up to 35 for the reasons you stated, then let it fall to 25 in the glide before repeating.

 

Bob, could you explain those series a bit more than the top descriptions?