Slower speed & increased fuel economy? (1 Viewer)

[canman]

Has anyone been driving less than 100 kph (62 mph) in order to increase fuel economy, and if so, what kind of difference have you seen?

I've recently slowed down on the highway to 85-92 kph (53-57 mph) from 110-115 kph (68-71 mph), and it seems to improve my fuel economy quite a bit, but I have no hard data yet. Around 90-92 kph, engine speed is around 1800 rpm on my 315s which seems to be a sweet spot.

 

[baldilocks]

This is why speed limit was reduced to 55 in the 70's. Beyond 60 mph wind drag increases sharply the faster you go. dimishing returns for the fuel burned.

 

[landcruiser80]

My great uncle was driving way out in the woods one time when he saw his fuel light come on.
He just went verrrry slowly down the road and was able to drive 1.5 hours out of the bush, down the main road, and to the nearest gas station.
I don't know how much of a difference small deviations at high speed make but if you really cut down on your speed, then...30mpg???

 

[coax]

Yep the drag is relative to the square of the velocity, so small reductions make fairly large gains. I recall hearing somewhere that the best speed for gas mileage was around 40-50mph, depending on the vehicle.

 

[Landseer]

Doesn't show a LC but gives you a general idea.
http://upload.wikimedia.org/wikipedia/commons/a/a9/Fuel_economy_vs_speed_1997.png

 

[bmac1996acc]

Normal driving gives me 11.5-12 mpg. On a recent trip I was driving more leisurely than normal which included only driving 55 mph on state highways where I normally would drive 65-70 mph. I got 14.2 mpg on that trip.

 

[Frankencruiser]

When I moved from Colorado I drove the 80 behind the moving van. Top speed 55mph. Slooooooooooow up hills (like 25-30mph). It averaged an almost inconceivable 18.7mpg over 1400 miles.

I'll never drive that slow by choice.

 

[surfpig]

When I moved from Colorado I drove the 80 behind the moving van. Top speed 55mph. Slooooooooooow up hills (like 25-30mph). It averaged an almost inconceivable 18.7mpg over 1400 miles.

I'll never drive that slow by choice.

^THIS^



I've done the same. Drive under 65mph on the same boring-ass stretch of road for hours upon hours. You do see a significant improvement.

 

[Stylo07]

When I moved from Colorado I drove the 80 behind the moving van. Top speed 55mph. Slooooooooooow up hills (like 25-30mph). It averaged an almost inconceivable 18.7mpg over 1400 miles.

I'll never drive that slow by choice.

That's just it, 50-60 mph will yield better fuel economy, but many aren't willing to do so due to impatience, reluctance to be a disturbance to faster moving traffic, or otherwise. I recently tried going slower on my highway drives (55-60) and got 13 mpg with 35s and some mixed city driving.

 

[inkpot]

Now you know why old farts drive so slow. They've been doing the math for years. Why hurry when you don't have to, and ya save some $$$ in the process.

 

[baldilocks]

Owning an 80 implies that fuel economy is not at the forefront of the owners thoughts in the first place. I confess that I welcome a good long stretch of downhill though.

 

[BILT4ME]

I recently took a 7 hour trip and I chose a route that was 30 miles shorter but the speeds were 65 mph max speed limit vs interstate driving of 70 mph. I chose the lower speed route and averaged 15.75 mpg vs the interstate route average at 13.5 mpg. The interstate route I would drive 78 mph and the other route I would drive 58-65. Time difference between the two routes was 10 minutes longer on the slower route. If I drive the LC again, I will take the scenic route. If the minivan I will take the interstate.

 

[leonard_nemoy]

With my old tacoma with the 2.7 4 liter I would average 18 mpg on the interstate. I drove the entire length of utah on highway 89 speeds anywhere from 40 to 65 max and avergeed 24 mpg.

 

[Random Dan]

My Dad's 80 with 200,000+ miles, ARB bar with Warn, Kaymar rear, and 35s on a 4 inch OME lift got about 15mpg doing 75 on the interstate on its last road trip. In town it averages about 12-13.

 

[cruiserdan]

The 80 was designed when the maximum legal speed limit was 55MPH.

Take a guess at the target cruising speed during the design process.....

 

[inkpot]

The 80 was designed when the maximum legal speed limit was 55MPH.

Take a guess at the target cruising speed during the design process.....

Yup! There are still a few of us that remember the Double Nickel Days. Sucked!!

 

[ironhippy]

I can get significantly better fuel mileage in the 80 - 100 km range. If I'm travelling long distances, I normally just say "screw it, I'm gonna pay to get there faster" and forget about fuel mileage.

I don't take long trips in the Cruiser unless I need to, or I am going to be spending significant time off road

 

[Qball]

I can get significantly better fuel mileage in the 80 - 100 km range. If I'm travelling long distances, I normally just say "screw it, I'm gonna pay to get there faster" and forget about fuel mileage.

I don't take long trips in the Cruiser unless I need to, or I am going to be spending significant time off road

Yup! If I drive 60-65 on fairly flat ground with heavy 35 AT tires and 2 inch lift I can get close to 16mpg, but that takes patience and work.

Most of the time I go with speed of traffic or just shy of. Since I don't drive the LC or LX as DD, difference in saving is minimal because I normally fill up once or twice a a month max.

 

[Golgo13]

Yep the drag is relative to the square of the velocity, so small reductions make fairly large gains. I recall hearing somewhere that the best speed for gas mileage was around 40-50mph, depending on the vehicle.

coax nailed it above. From Wikipedia "Drag Equation":

Mass density, Reference Area, and Drag Coefficient do not change for the case of driving down the highway.
Force of drag increases with the square of your velocity.
If you get really technical about it, you find that at low speeds, the velocity isn't really enough to cause appreciable drag. At higher speed, everything becomes limited by drag.

Now, if you multiply the Force of Drag from above by the speed of the vehicle, this will tell you how much horsepower is necessary at the wheels to maintain that speed. Throw in factors for driveline efficiency, transmission efficiency, and rolling resistance or the tires, and you can get a good idea of the vehicle's required power output from the engine.

To get REALLY detailed you can do some fancy calculus to include the accelerations of the vehicle speeding up and slowing down. Then you can use all this information to calculate the rate of gasoline mass flow from the injectors.

Then when you're done with that they give you a diploma and you never do calculations like that again.

 

[cruiserdan]

Then when you're done with that they give you a diploma and you never do calculations like that again.

Sig line material right there folks.....