How fast can you go and still get <acceptable> MPGs?

quixotequest · 08-10-2007, 12:37 PM

Last week we were able to take our first ~2000 mile road trip in our young Prius. (Just had it's second oil change this week.) Anyway, not knowing how "broken in" our car really is still at this point, and also wanting to eat up miles to get to our destination as soon as possible while still delivering decent MPGs, I played a lot around with finding the "sweet spot" between max speed and fuel economy. And understanding what others will consider a "sweet spot" to be is relative, here's what we observed:

1) Normally, on road trips, with our other cars, I have operated with 9mph over the limit cruise control setting, except in populated areas which is usually 4 or 5 mph over. (SO I'm one of those people who push the limits of what speed is allowed without making myself likely to be pulled over.)

2) In Idaho, where 75mph is the highest limit permitted on our trip from Utah to the Oregon coast, we tried driving at 84mph. Ambient temps were in the 80s. In some places was in the low-mid 90s. A/C only ever ran as high as the second mark (I dislike the Auto setting so always alternate settings manually). And sometimes, when it got a little chilly we shut it off. While there were some hills and descents, we were traveling on a gradually downward course from about ~4400 elevation in Utah to ~2800 elevation in Boise. (The highest the elevation ever got again was in the Blue Mountains near Pendleton.) Whether on cruise or using the pedal I was not able to eek out higher than a 33 mpg. But dropping cruise to 79 I was able to push out average mpgs to the mid 40s. By working the pedal myself with "pulse and glides" I could squeek out the highest avg mpg of 47mpg. (However, coming back home across Oregon and Idaho, where we had more wind to push against, plus a gradual climb to a higher elevation, keeping the similar speeds I was only able to obtain 43-44 avg mpg.)

SO the sweet spot for our experience seemed to be around 78-79mph was the fastest we could travel and still get what I considered an acceptable avg mpg, which was a goal to at least be in the mid 40s mpg.

Headed across Oregon where the highest we aimed to travel was 9 over 65mph (across eastern part of state--still quite a few hills and mountains) or 5 over 55mph (hilly, twisty areas around the coast) we were able to eek out between 49mpg to as high as 51.5mpg on average. We expected this as slower high speeds most always result in higher MPGs.

But what interested me the most is seeing how fast we could drive, in areas that allowed it, before the Prius' MPGs really came crashing down. (It also makes me wish the MFD would display a graph of average speeds and other useful environmental factors charted against fuel economy.)

###

What are others' experiences like?

scm2000 · 08-10-2007, 01:35 PM

Quote:

Headed across Oregon where the highest we aimed to travel was 9 over 65mph (across eastern part of state--still quite a few hills and mountains) or 5 over 55mph (hilly, twisty areas around the coast) we were able to eek out between 49mpg to as high as 51.5mpg on average. We expected this as slower high speeds most always result in higher MPGs.
[/b]

I drive in NY state and the max highway speed limit is 65mph on remote areas of interstates and 55mph on local stretches of interstates.
I always drive the speed limit unless conditions indicate I should drive slower so I can not comment on speeds above 65mph, but....
My experience in driving 55 or 65mph is that you get about 55mpg for either of those speeds. I've traveled at 55mph on the rather hilly roads around lake ontario for long distances and got the same mpg.

This is on a new 07 Prius with about 2500 miles on it.

I know you were looking for comments regarding speeds in the 70's and above but I noted that you said you were getting 49-51.5mpg at similar speeds as mine.

Devil's Advocate · 08-10-2007, 01:48 PM

85 mph uphill (5-6%) 39 mpg
75 mph towing two motorcycles uphill (same hill) 29 mpg
100 mph flat ground 34 mpg
lifetiem average 115,000 miles 42 mpg

bwilson4web · 08-10-2007, 03:39 PM

The "I-90" curve is from an NHW20, 2004-current Prius. The other data points are from an NHW11, 01-03 Prius.

For slow speeds:

The cluster of black dots between 25-30 mph are from the NHW20, 2004-current Prius marathon of about two years ago. The other curves and points are for an NHW11, 01-03 Prius.

Bob Wilson

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
What IS the maximum acceptable inverter temp??	JimboK	Gen II Prius Technical Discussion	14	08-01-2008 10:13 PM
Are Winshield Repairs acceptable alternative to replacement?	NoMoShocks	Gen II Prius Main Forum	19	05-25-2007 03:28 AM
25.8 average MPGs for the day!!!	Kacey Green	Other Cars	0	08-31-2004 08:34 PM
why estimate mpgs?	jamarimutt	Gen II Prius Fuel Economy	38	08-09-2004 11:23 PM
Had BIG jump in MPGs	Brian	Gen II Prius Fuel Economy	2	06-18-2004 02:30 PM

08-10-2007, 12:37 PM	#1
quixotequest Member Join Date: Jul 2007 Posts: 39 My Car: Model: Package: Thanks: 0 Thanked 1 Time in 1 Post Friends: 0	Last week we were able to take our first ~2000 mile road trip in our young Prius. (Just had it's second oil change this week.) Anyway, not knowing how "broken in" our car really is still at this point, and also wanting to eat up miles to get to our destination as soon as possible while still delivering decent MPGs, I played a lot around with finding the "sweet spot" between max speed and fuel economy. And understanding what others will consider a "sweet spot" to be is relative, here's what we observed: 1) Normally, on road trips, with our other cars, I have operated with 9mph over the limit cruise control setting, except in populated areas which is usually 4 or 5 mph over. (SO I'm one of those people who push the limits of what speed is allowed without making myself likely to be pulled over.) 2) In Idaho, where 75mph is the highest limit permitted on our trip from Utah to the Oregon coast, we tried driving at 84mph. Ambient temps were in the 80s. In some places was in the low-mid 90s. A/C only ever ran as high as the second mark (I dislike the Auto setting so always alternate settings manually). And sometimes, when it got a little chilly we shut it off. While there were some hills and descents, we were traveling on a gradually downward course from about ~4400 elevation in Utah to ~2800 elevation in Boise. (The highest the elevation ever got again was in the Blue Mountains near Pendleton.) Whether on cruise or using the pedal I was not able to eek out higher than a 33 mpg. But dropping cruise to 79 I was able to push out average mpgs to the mid 40s. By working the pedal myself with "pulse and glides" I could squeek out the highest avg mpg of 47mpg. (However, coming back home across Oregon and Idaho, where we had more wind to push against, plus a gradual climb to a higher elevation, keeping the similar speeds I was only able to obtain 43-44 avg mpg.) SO the sweet spot for our experience seemed to be around 78-79mph was the fastest we could travel and still get what I considered an acceptable avg mpg, which was a goal to at least be in the mid 40s mpg. Headed across Oregon where the highest we aimed to travel was 9 over 65mph (across eastern part of state--still quite a few hills and mountains) or 5 over 55mph (hilly, twisty areas around the coast) we were able to eek out between 49mpg to as high as 51.5mpg on average. We expected this as slower high speeds most always result in higher MPGs. But what interested me the most is seeing how fast we could drive, in areas that allowed it, before the Prius' MPGs really came crashing down. (It also makes me wish the MFD would display a graph of average speeds and other useful environmental factors charted against fuel economy.) ### What are others' experiences like?

08-10-2007, 01:48 PM	#3
Devil's Advocate Senior Member Join Date: Mar 2005 Location: Las Vegas, Nevada Posts: 913 My Car: 2005 Prius Model: Package: #9 Thanks: 0 Thanked 1 Time in 1 Post Friends: 0	85 mph uphill (5-6%) 39 mpg 75 mph towing two motorcycles uphill (same hill) 29 mpg 100 mph flat ground 34 mpg lifetiem average 115,000 miles 42 mpg

08-10-2007, 03:39 PM	#4
bwilson4web 03 and 10 Prius Join Date: Nov 2005 Location: Huntsville AL with 2003 Prius Posts: 3,885 My Car: 2010 Prius Model: III Package: #1 Thanks: 148 Thanked 369 Times in 205 Posts Friends: 20	The "I-90" curve is from an NHW20, 2004-current Prius. The other data points are from an NHW11, 01-03 Prius. For slow speeds: The cluster of black dots between 25-30 mph are from the NHW20, 2004-current Prius marathon of about two years ago. The other curves and points are for an NHW11, 01-03 Prius. Bob Wilson