Optimal cruising interstate speed

[wilto]

Good Morning!

We are travelling to Orlando next week for a week at Disney, this is our first road trip in the PF (4.0 V6) and it's about 450 miles from my house to Disney , it will be interstate all the way.

I worked it out 450/21 (gallons) is about 21.5 MPG so if we can get above that and make it on one tank I will be very happy!

From your experiences what is the best cruising speed in which to reach the max MPG? Also would premium make a difference?

[skinny2]

Physics would tell you the best economy is at the slowest speed in the highest gear. Lets rule out anything south of 65mph...you'll get killed. If I keep it around 70mph I can get 21-22mpg and that's in hilly terrain. Plus I'm 4x4 and I'm guessing you're not. I don't see a big change in mpg until I go up over 80..which is usually where I run. I get 20mpg on long highway trips at that speed.

I think that's a pretty easy target but the problem is you don't want to use all 21 gallons...in fact I've never gone more than 19.5 gallons and that's many miles after the light has come on and my DTE is screaming at me to get fuel.

Premium makes a very slight difference if you're driving hard. I've never clocked a mpg difference for highway driving. I usually try to buy a good 87 octane (bp seems to eliminate all knocking for me) and live with slightly lower performance. I sometimes will mix in some 89 or 93 particularly if I'm towing but again, I don't see much mpg difference. It's strictly for performance.

Oh, and sorry about the Disney thing

[martyf250]

i have an 05 4x4. On trips from RI to NJ 256mi one way i used to get best gas mileage at 60MPH-65MPH....and would be able to break the 25MPG barrier. Of course the speed limit was 65 and everyone else was doing 75+ so you would get a lot of dirty looks

[deermjd]

On a recent road trip I averaged 21 mpg going 70-75. The speed for optimum gas mileage would probably around 60 but at that speed your concern is not getting killed rather than gas mileage.

[hfrez]

I noticed that wind speed and direction will also influence your gas milage greatly. With headwind I got as low as 17.5mpg and from beind I got 23mpg's once or twice.

[leadpig]

I've found very approximately that 60/70/80 mph returns about 21/20/19 mpgs. The load on the little picture to the left got 17.9 at about 75. That's with 91 octane.

[FLiPMaRC]

I noticed that wind speed and direction will also influence your gas milage greatly. With headwind I got as low as 17.5mpg and from beind I got 23mpg's once or twice.

So true! I had that happened to me a few times.

[skinny2]

I noticed that wind speed and direction will also influence your gas milage greatly. With headwind I got as low as 17.5mpg and from beind I got 23mpg's once or twice.

So true! I had that happened to me a few times.

Same here. A couple days a week I drive 70 miles to work due west and 99.5% of the miles are highway. I've had mpg as low as 17 during horrible headwinds and as high as 22 on a normal day. Heading back home due east I've seen anything from 21-25 depending on speed and traffic. The tail wind doesn't help you as much as the headwind hurts you!

[smj999smj]

I've never had any noticeable differance in mpg on a long trip using premium fuel versus regular 87 octane. For the size of the vehicle, R51's do pretty good on fuel mileage when cruising the highways, in part to the 5 speed AT. It's the stop and go and around town driving that takes its toll on the fuel mileage! I use the cruise control as much as possible and try to take it easy on the pedal. My last 400 mile jount from southern VA to central NJ netted me a 19.5 mpg average doing 70 to 80 most of the time. I even hit 24 mpg in my 06 LE 4X4 on a particular stretch of I-95 doing 65mph! I was all, "Whoo-hoo!"

[JAHBLESSINGS]

i drive 65 mph and get around 24-26 on the mpg computer.

[res0ippr]

More on physics: drag force depends on the area-squared for large objects like the pathy so avoid putting things up there. Drag force also depends on the speed-squared for speeds greater than 60-65 MPH so keep it around there.

Air temperature also plays a factor so deffinitely drive early morning or night. Lastly, avoid stops as acceleration kills MPG (I know some of these already mention).

Let us know how it worked out...

[doctahjones]

my unscientific observations have been that i get the best mpg's when setting cruise to 60-65. i lose about 1mpg per 5mph over that.

hard part is i generally like doing 70-80 (depending on road and speed limit) so i had been averaging about 17-18 when i do all hwy.

i have the air raid installed and initially though i got a huge boost in mpg during a test, but there must have been a tailwind as i haven't been able to repeat the 20+mpg i got during that test.

plus as it gets hotter here my mpg seems to be (at least last year it did) about 3-5mpg less than in the winter/mild months. i'm guessing this should be because the ac running all the time and high air temps cause less fuel burn (or whatever the technical/scientific term for it is).

[jking63]

I lost 1.5mpg when I replaced my H/L tires with A/T's.

[wilto]

Ok well the trip is done and we are back home and I got about 20.5 and stuck to 70 mph.

There were some road works where I had to go 50 and then some areas where I went 75 so averaged out to 70 mph.

[Mark21]

Sooo. I am amazed to see the mpg you guys are getting. I have a 2005 SE and have never gotten better than 18-19 on long drives. I usually have cruise set on 78 all the way. I always wondered how accurate the mpg gauge was. Am I missing something here or are the newer models that much better on gas.