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Has anyone experimented with various driving speeds to try to determine best speed to optimize fuel milage. I normally cover a lot of ground quickly at about 80 mph and I have noticed that my milage does not seem any better at 60mph than at 80. Anyone found a sweet spot?
 

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I've never tried in the FJ. I used to play the game in the Civic Hybrid. Best I could do was 58 mpg on the daily drive. Mostly I watch the gas gauge and think "Oh crap, I'm down to half a tank and it's only Tuesday. Need to calm down."
 

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I don't drive that fast..

Jade does pretty well 45-55, two lane and 60 hiway (hiway limit here is 65.) I'm always surprised how well she does on the back roads under 25 4HI or 4LO.

FJ's are bricks and Jade doesn't do well over 60.

Jade weighs in at 5500, full of gas and three of us + gear.. (tires, bumpers, winch, tools, recovery drawer etc.) I'm happy when I see 15+

I don't worry about the mileage and I carry extra 10 gal gas. ?
 
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I get great gas mileage when I drive over 5000 ft. Not so great at sea-level. Up to 60 or 70 more miles to a tank when the air is thin. :)
 

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Has anyone experimented with various driving speeds to try to determine best speed to optimize fuel milage. I normally cover a lot of ground quickly at about 80 mph and I have noticed that my milage does not seem any better at 60mph than at 80. Anyone found a sweet spot?
This is crazy. Have you ever driven a full tank of gas at 60 and then a full tank at 80 in the same weather conditions . ( temp/wind direction).

The FJ is a brick. Once it starts pushing any significant wind(which starts about45-50mpg) Every speed increase will see a fuel increase.

Against a strong headwind mileage will be better in 4th , than 5th in auto trans running 60mph.

Type of tire(weight/tread/diameter) also has significant bearing.

Considering what higher speed mpg is, I am always amazed how good the mileage is knocking around on backroads where speed is 25-35mph. ( remote rural areas)


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My supercharged '08 (stock tires and suspension) gets 15mpg at 75mph. It'll go 90 all day long (in the desert, in Utah, where the speed limit is 85 and its actually pretty hard to pass semi trucks), but only get 11~12mpg.

So, in answer to OPs question, as several others have said, 45mph is the ideal speed for maximum mileage, mine gets 21mpg when I go a whole tank at 45mph (with as little starting/stopping as possible).

Wind drag goes up by the square of the velocity, and for Automobiles, and mpg, it is typically said that aerodynamic drag only starts to become an issue above around 45mph.
 

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I usually cruise at 62-63mph no matter the limit. I've found that speed to be a good balance between speed vs mpg.

We took a trip once and pushed along at 75-80 the whole way and ended up getting 9mpg instead of our normal 11-12mpg.
 
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Get an ultraguage and see for yourself. I find 50mph to be the best mpg in my case.

 

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A lot of manufacturers put their sweet spot for hwy driving straight up on the speedometer. Which on the FJ is basically 60mph. Most of your mpg depends on your acceleration though, aka the driver. In addition to engine type, 4wd/2wd, manual/automatic, vehicle condition/repair, modifications, elevation or weather conditions. So it really can vary greatly from person to person. And yeah shockingly to me too, FJ’s can do 80mph easily, lol. Although not recommended in high winds. It’s down right scary passing semis at those speeds in high winds. Driving back from California to Texas I was roughly 75mph to 80mph, averaging about 300 miles per tank.
One thing to add, I also noticed an oddity with my FJ. (I’m not sure if it’s the same for everyone) While my speedometer was reading 80mph Waze was clocking me at 78mph. So either the the FJ speedometer is off, or Waze is. Mines a stock 2011 trail teams, on oem bfg all terrains.
 

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80 vs 78 is only 2.5%, well within tolerance, considering tire variation and everything else manufacturing-wise
 

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I've noticed for city driving around 45mph I get 20mpg if there's no/light traffic, as for freeway driving, I can get 18mpg if I keep it at 60mph but that number drops to like 10mpg if I do 70-80mph
 

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I have gotten as high as 22 mpg on a 2-lane 60 mph highway, which is about 3 mpg more than I get at 75 mph...depending on wind direction and speed.
 

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I keep it around 75mph on freeways as the mileage drops way off if I go to 80. I'll get 20-23mpg on I-70 from Denver area to Utah.
 

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I can't take credit for the detailed information below. I believe that I copied it from a thread a some time ago because it looked so comprehensive.

Speed and fuel based efficiency

The FJC has a drag coefficient of .40 without the roof rack, .43 with it.

Frontal area is 31.5 square feet.

So, aerodynamic resistance (Aero horsepower) at 100 km/h (62 mph) is 39.1 hp.

(The above is all stock - adding or changing anything will probably add to the Cd and the frontal area).

4500 pounds curb weight with driver only. No extra stuff like all you guys like to haul around.

I used 0.03 as a ballpark rolling resistance for an All-Terrain tire at 36PSI on asphalt.

Summertime fuel has a stored energy of 114,500 BTU.

I used .22 as engine efficiency. Ballpark, as Toyota doesn't advertise that. It's likely somewhere between .20 and .25, so I split the difference.

Drivetrain efficiency I estimated at .85. 6MTs are inherently less efficient than 5ATs because of the full-time 4WD and the Torsens all over the driveline.

Air density at 68 degrees F is 1.204 kg/m3 / 0.52 psi per 1000 feet

Variables for these results:
  • Vehicle weight: 2041.2 kg / 4500 lbs
  • Crr: .0.03
  • Cd: .43
  • A: 2.9 m2 / 31.5 ft2
  • Fuel energy density (Wh/US gal.): 33557
  • Engine efficiency: .22
  • Drivetrain efficiency: .85
  • Parasitic overhead (Watts): 0
  • rho: 1.204 kg/m3
So here are the results:
  • 65MPH - 21.95 MPG
  • 70MPH - 18.92 MPG
  • 75MPH - 16.48 MPG
  • 80MPH - 14.49 MPG
  • 85MPH - 12.83 MPG
The above numbers are an estimate only (we have a few variables with nothing but an educated guess), but it does illustrate the relationship between highway speed and MPG.

Note that you only get 66% of your 65MPH mileage at 80MPH. You're sacrificing a lot of MPG for a 23% speed increase. Plus the added attraction of tickets from The Law.

The next thing I did was calculate the range of a tankful of gas at different speeds, using 18 gallons as a tankful. I left an extra gallon of gas in the tank as cushion.
  • 80MPH = 260 miles.
  • 65MPH = 395 miles.
  • 80MPH = 3:15 driving time between fill-ups.
  • 65MPH = 6:00 driving time between fill-ups.
Hope that helps, as I am not a huge fan of public displays of math.
So then you start calculating how long gas stops take, how much you want to spend on fuel (summer of '14 we were seeing mostly $4.50/gallon in the West, so fill-ups were $70-80), and how much your time is worth to you. It's a fun exercise, and very illuminating.
 

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I have gotten as high as 22 mpg on a 2-lane 60 mph highway, which is about 3 mpg more than I get at 75 mph...depending on wind direction and speed.
I have noticed that I consistently get 4 to 5 mpg better in the high country (Million Dollar Highway) than I do back home in Texas. FJ is a brick but right now gas is cheap. When gas is cheap you can throw MPG out the window. Hammer Down!
 

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I can't take credit for the detailed information below. I believe that I copied it from a thread a some time ago because it looked so comprehensive.

Speed and fuel based efficiency

The FJC has a drag coefficient of .40 without the roof rack, .43 with it.

Frontal area is 31.5 square feet.

So, aerodynamic resistance (Aero horsepower) at 100 km/h (62 mph) is 39.1 hp.

(The above is all stock - adding or changing anything will probably add to the Cd and the frontal area).

4500 pounds curb weight with driver only. No extra stuff like all you guys like to haul around.

I used 0.03 as a ballpark rolling resistance for an All-Terrain tire at 36PSI on asphalt.

Summertime fuel has a stored energy of 114,500 BTU.

I used .22 as engine efficiency. Ballpark, as Toyota doesn't advertise that. It's likely somewhere between .20 and .25, so I split the difference.

Drivetrain efficiency I estimated at .85. 6MTs are inherently less efficient than 5ATs because of the full-time 4WD and the Torsens all over the driveline.

Air density at 68 degrees F is 1.204 kg/m3 / 0.52 psi per 1000 feet

Variables for these results:
  • Vehicle weight: 2041.2 kg / 4500 lbs
  • Crr: .0.03
  • Cd: .43
  • A: 2.9 m2 / 31.5 ft2
  • Fuel energy density (Wh/US gal.): 33557
  • Engine efficiency: .22
  • Drivetrain efficiency: .85
  • Parasitic overhead (Watts): 0
  • rho: 1.204 kg/m3
So here are the results:
  • 65MPH - 21.95 MPG
  • 70MPH - 18.92 MPG
  • 75MPH - 16.48 MPG
  • 80MPH - 14.49 MPG
  • 85MPH - 12.83 MPG
The above numbers are an estimate only (we have a few variables with nothing but an educated guess), but it does illustrate the relationship between highway speed and MPG.

Note that you only get 66% of your 65MPH mileage at 80MPH. You're sacrificing a lot of MPG for a 23% speed increase. Plus the added attraction of tickets from The Law.

The next thing I did was calculate the range of a tankful of gas at different speeds, using 18 gallons as a tankful. I left an extra gallon of gas in the tank as cushion.
  • 80MPH = 260 miles.
  • 65MPH = 395 miles.
  • 80MPH = 3:15 driving time between fill-ups.
  • 65MPH = 6:00 driving time between fill-ups.
Hope that helps, as I am not a huge fan of public displays of math.
So then you start calculating how long gas stops take, how much you want to spend on fuel (summer of '14 we were seeing mostly $4.50/gallon in the West, so fill-ups were $70-80), and how much your time is worth to you. It's a fun exercise, and very illuminating.
smcgee -
Very clearly presented relationship between vehicle speed, drag, and resulting fuel consumption - well done.

Your numbers correlate very closely with what I have seen over the last 5 years with my '14.
 
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