Most efficient speed for best MPG?

Swamibob · 01-24-2006, 12:36 PM

Does anyone know what the most efficient speed for the 2006 Prius is? I know running off the battery would be the most efficient, but I mean as far as highway driving for long stretches, what is the speed I should set my cruise on to get the best MPG? This would be on level ground and assume no headwind or tailwind.

Thanks,
Swamibob

tumbleweed · 01-24-2006, 12:55 PM

What I have observed is generally speaking slower is better. Of course at 0 mph we get 0 mpg and at some speed, say 70 mph at 65 degrees F, we might get 48 mpg. Well we know we can beat both of those numbers and I expect your question is at what speed does the graph peak out. I think it will depend on a lot of things even if the terrain is dead level with no wind, such as: temprature, tire pressure, use of heat and air conditioning, and a bunch of other things. But in any case I expect the best mileage will be at some speed, say 30 or 35 mph, that is really to slow to drive for long distance. Best thing is to experiment when you can.

BTW driving on the battery is not always the most efficient way to get down the road, remember that all of the energy in the battery has to be put there by burning gasoline. For example, if you come down a hill and put a lot of energy in the battery you had to get up the hill to start with. The battery is great though because it lets you recover some energy you would otherwise throw away.

Check some of the older topics in this forum by efusco and others. There is really a wealth of good information here.

Edit: I should add that using energy in the battery is indeed a good idea and if you can do it with the ICE off so much the better. It's just that you shouldn't drive with storing energy as a goal.

Jack 06 · 01-24-2006, 01:14 PM

One of the "mad scientist"-type engineers who sprang up when the Gen 1 Prius was first getting analyzed on the Yahoo groups produced a grid predicting MPG at all speeds, and taking into account factors such as ambient temperature and wind speed. I don't remember where that might actually reside, but I'll bet either john 1701a or Dr. Fusco does. Seems the "sweet spot" was somewhere between 50 and 55, but I'm not sure. If john or Dr. Fusco don't see this and respond, I'll PM one of them. Some other analysis may have emerged since then, anyway, that I'm not aware of.

**efusco** · 01-24-2006, 03:25 PM

The 64mph "Sweet spot" once proposed on his site is not true.
The best MPG will be on level terrain b/w 30-40mph. Lower forces the ICE to run too much in a low efficiency state. Higher and drag becomes the bigger factor. It's a linear thing and there's nothing magical about 64mph or 53mph or any other number.

kDB · 01-25-2006, 08:12 AM

Quote:

Originally posted by efusco@Jan 24 2006, 03:25 PM
The 64mph "Sweet spot" once proposed on his site is not true.
The best MPG will be on level terrain b/w 30-40mph...

[snapback]196388[/snapback]

i agree, though for me anywhere between 35 and 50mph give me 55+mpg on near-flat streets. i'd say around 42 would be a good place to start testing. but when you start adding in head/tailwinds, hills, etc... it makes it hard to define an accual number.

and driving on battery only usually isn't a good idea to get better milage. sure it will look like a huge increase while your doing it, but not later when your burning gas to replace the charge. generally i only use ev mode at under 15-20, when i want to burn off a green charge, or when i know i have a long downhill coming soon that will recharge me to green.

tomdeimos · 01-25-2006, 08:39 AM

The best mpg is on battery only at around 30 mph.
You should easily achieve over 70 mpg.

kDB · 01-25-2006, 08:55 AM

well if your talking instantanious mpg battery would be better, but you have to get that electricity from somewhere, and usually it's from burning fuel.
but even if you are talking instantanious, simply gliding without battery or gas would be best. i guess it's all in what terms you use.

the way i read it made me answer this way. if i were to use a whole tank of gas on a nascar style oval track. what speed would be best to drive at with constant pressuse on the pedal (i.e. trying to keep as close to the same rate of gas flowing into the ICE at all times). now since i don't have the money to rent a track to test on (i wish i did, we could answer this once and for all, well at least until you start throwing in pulse and glide, etc.), i answered what i usually average driving to work and back.

now sure you can argue that you have the regenerative braking, but even then there are limit to where it helps. overall, i try to not charge the battery, but i also don't try to use the charge much either. and as you can tell from my tanks (click link in sig), i can do fairly well. there are only a few times i have averaged below 50mpg on a tank. there are the first few tanks because of me learning how to deal with the problems filling the tank. and three others. one at 49mpg, and two at around 45mpg. the two at 45 were me trying my hardest to drive the car like a normal person would, with the heat up fairly high (normally i don't use heat unless it's below 30 outside, and then just enough to get the cabin to around 45).

tomdeimos · 01-25-2006, 09:57 AM

The battery is why the Prius works. The more you can use it the better. It is completely useless to try not to use it. You can't at 40 mph or below. The car will not let you.

The only reason for having a hybrid is to benefit from using as much battery power as possible. It is way more efficient and the 70 mpg I mentioned is the min mpg I can achieve daily if I drive slow, which is not very often.

It is true you can do better not using the battery by coasting, and get mpg more up toward 100 mpg but I do not find that practical or possible where I drive.

If you try to run on the gas engine all the time you are guauranteed less mpg for other cases.

kDB · 01-25-2006, 10:13 AM

the battery system itself is not the reason the prius works. yes, it is one of the main parts, but there is pleny of other stuff there. theres the ICE, very efficient, and it turns off when not needed. there's also the low drag coefficent...

the fact is, the electricity in the battery comes from somewhere, and unless your plugging the car in and getting it from the grid, have a solar setup, ect., it's coming from the ICE. sure there's the regenerative braking, but something has to speed you up first so you can use that. EV for speed... your back to needing a source of electricity, and eventually in this loop you'll run out due to friction of the road and inefficient electricity transfer to and from the parts in the system.

tomdeimos · 01-25-2006, 11:12 AM

You're correct there are other efficiency improvements in the Prius. But the battery is a major one at low speeds.

You can't get the super mpgs by using the engine. I have tried at various speeds. I always get better mpg on battery driving on flat roads at 40 mph than on engine at 43 mph. My best mpg is always when I am on battery about 2/3 or more of the time and I can drive at a steady speed.

Any time the engine is going full time I generally get mpg's that are always below 70 mpg. This includes slow driving in winter too, when it is too cold for the engine to stop.

01-24-2006, 12:55 PM	#2
tumbleweed Senior Member Join Date: Oct 2005 Location: Eastern Oregon Posts: 1,692 My Car: 2010 Prius Model: V Package: Adv. Technology Thanks: 33 Thanked 104 Times in 84 Posts Friends: 0	What I have observed is generally speaking slower is better. Of course at 0 mph we get 0 mpg and at some speed, say 70 mph at 65 degrees F, we might get 48 mpg. Well we know we can beat both of those numbers and I expect your question is at what speed does the graph peak out. I think it will depend on a lot of things even if the terrain is dead level with no wind, such as: temprature, tire pressure, use of heat and air conditioning, and a bunch of other things. But in any case I expect the best mileage will be at some speed, say 30 or 35 mph, that is really to slow to drive for long distance. Best thing is to experiment when you can. BTW driving on the battery is not always the most efficient way to get down the road, remember that all of the energy in the battery has to be put there by burning gasoline. For example, if you come down a hill and put a lot of energy in the battery you had to get up the hill to start with. The battery is great though because it lets you recover some energy you would otherwise throw away. Check some of the older topics in this forum by efusco and others. There is really a wealth of good information here. Edit: I should add that using energy in the battery is indeed a good idea and if you can do it with the ICE off so much the better. It's just that you shouldn't drive with storing energy as a goal. __________________ Tom

LinkBacks (?) LinkBack to this Thread: http://priuschat.com/forums/gen-ii-prius-fuel-economy/14675-most-efficient-speed-best-mpg.html
Posted By	For	Type	Date
Mercury Mariner Mpg, New Mercury Mariner Hybrid For Sale White, Mariner Outboard Motor Pictures - Cowhidemirror	This thread	Refback	03-09-2009 06:13 AM
Understand the MPG meter (one more time) - GreenHybrid - Hybrid Cars	This thread	Refback	05-17-2008 12:28 AM
Comments on the FAQ - Page 2 - GreenHybrid - Hybrid Cars	This thread	Refback	02-01-2008 07:33 AM

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
EPA - Cars LESS Fuel Efficient Than In The 80s!	Areometer	Gen II Prius Fuel Economy	17	07-04-2008 12:17 PM
Energy-efficient californians	chogan	Environmental Discussion	8	02-27-2007 04:54 PM
Efficient speakers	Jmad1138	Gen II Prius Audio and Electronics	10	12-09-2006 01:19 PM
Prius less efficient at highway speed than two-mode hybrids?	sola	Gen II Prius Technical Discussion	11	06-15-2006 10:20 PM
Prius 1/3 as efficient...	texassalsa04	Gen II Prius Main Forum	5	01-10-2006 12:38 PM

01-24-2006, 12:36 PM	#1
Swamibob Join Date: Jan 2006 Posts: 12 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	Does anyone know what the most efficient speed for the 2006 Prius is? I know running off the battery would be the most efficient, but I mean as far as highway driving for long stretches, what is the speed I should set my cruise on to get the best MPG? This would be on level ground and assume no headwind or tailwind. Thanks, Swamibob

01-24-2006, 01:14 PM	#3
Jack 06 Join Date: Oct 2005 Location: Winters, CA: Prius capital of US. 30 miles W of Sacramento Posts: 2,567 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	One of the "mad scientist"-type engineers who sprang up when the Gen 1 Prius was first getting analyzed on the Yahoo groups produced a grid predicting MPG at all speeds, and taking into account factors such as ambient temperature and wind speed. I don't remember where that might actually reside, but I'll bet either john 1701a or Dr. Fusco does. Seems the "sweet spot" was somewhere between 50 and 55, but I'm not sure. If john or Dr. Fusco don't see this and respond, I'll PM one of them. Some other analysis may have emerged since then, anyway, that I'm not aware of.

01-24-2006, 03:25 PM	#4
efusco Troll Slayer Join Date: Nov 2003 Location: Nixa, MO Posts: 17,228 My Car: 2004 Prius Model: Package: #9 Thanks: 49 Thanked 249 Times in 148 Posts Friends: 37	The 64mph "Sweet spot" once proposed on his site is not true. The best MPG will be on level terrain b/w 30-40mph. Lower forces the ICE to run too much in a low efficiency state. Higher and drag becomes the bigger factor. It's a linear thing and there's nothing magical about 64mph or 53mph or any other number.

01-25-2006, 08:39 AM	#6
tomdeimos Join Date: Feb 2004 Location: Lexington, MA Posts: 995 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	The best mpg is on battery only at around 30 mph. You should easily achieve over 70 mpg.

01-25-2006, 08:55 AM	#7
kDB Join Date: Jun 2005 Location: Fenton, MO Posts: 243 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	well if your talking instantanious mpg battery would be better, but you have to get that electricity from somewhere, and usually it's from burning fuel. but even if you are talking instantanious, simply gliding without battery or gas would be best. i guess it's all in what terms you use. the way i read it made me answer this way. if i were to use a whole tank of gas on a nascar style oval track. what speed would be best to drive at with constant pressuse on the pedal (i.e. trying to keep as close to the same rate of gas flowing into the ICE at all times). now since i don't have the money to rent a track to test on (i wish i did, we could answer this once and for all, well at least until you start throwing in pulse and glide, etc.), i answered what i usually average driving to work and back. now sure you can argue that you have the regenerative braking, but even then there are limit to where it helps. overall, i try to not charge the battery, but i also don't try to use the charge much either. and as you can tell from my tanks (click link in sig), i can do fairly well. there are only a few times i have averaged below 50mpg on a tank. there are the first few tanks because of me learning how to deal with the problems filling the tank. and three others. one at 49mpg, and two at around 45mpg. the two at 45 were me trying my hardest to drive the car like a normal person would, with the heat up fairly high (normally i don't use heat unless it's below 30 outside, and then just enough to get the cabin to around 45).

01-25-2006, 09:57 AM	#8
tomdeimos Join Date: Feb 2004 Location: Lexington, MA Posts: 995 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	The battery is why the Prius works. The more you can use it the better. It is completely useless to try not to use it. You can't at 40 mph or below. The car will not let you. The only reason for having a hybrid is to benefit from using as much battery power as possible. It is way more efficient and the 70 mpg I mentioned is the min mpg I can achieve daily if I drive slow, which is not very often. It is true you can do better not using the battery by coasting, and get mpg more up toward 100 mpg but I do not find that practical or possible where I drive. If you try to run on the gas engine all the time you are guauranteed less mpg for other cases.

01-25-2006, 10:13 AM	#9
kDB Join Date: Jun 2005 Location: Fenton, MO Posts: 243 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	the battery system itself is not the reason the prius works. yes, it is one of the main parts, but there is pleny of other stuff there. theres the ICE, very efficient, and it turns off when not needed. there's also the low drag coefficent... the fact is, the electricity in the battery comes from somewhere, and unless your plugging the car in and getting it from the grid, have a solar setup, ect., it's coming from the ICE. sure there's the regenerative braking, but something has to speed you up first so you can use that. EV for speed... your back to needing a source of electricity, and eventually in this loop you'll run out due to friction of the road and inefficient electricity transfer to and from the parts in the system.

01-25-2006, 11:12 AM	#10
tomdeimos Join Date: Feb 2004 Location: Lexington, MA Posts: 995 My Car: Model: Package: Thanks: 0 Thanked 0 Times in 0 Posts Friends: 0	You're correct there are other efficiency improvements in the Prius. But the battery is a major one at low speeds. You can't get the super mpgs by using the engine. I have tried at various speeds. I always get better mpg on battery driving on flat roads at 40 mph than on engine at 43 mph. My best mpg is always when I am on battery about 2/3 or more of the time and I can drive at a steady speed. Any time the engine is going full time I generally get mpg's that are always below 70 mpg. This includes slow driving in winter too, when it is too cold for the engine to stop.