Save Gas - Drive 55


#1

How much better gas mileage can I expect if I drive at 55 mph on the interstate instead of 80 like some of the type A personalities?


#2

Please don’t do this. Traffic moves like the water in a stream, and a car going 55 on the highway creates turbulance like a stone in a stream. Turbulance on the highway causes accidents.

Not to mention road rage. I don’t want to share my daily commoute with a whole bunch of “type A” drivers that you’ve just ticked off for the sake of saving a few bucks in gas.


#3

CU increased milage by 5 mpg for every 10 mph drop in speed in a Camry at freeway speeds. Pretty much depends on the auto/truck. Air resistance can amount to as much as 50% or more of the energy used at higher speeds. So you can see how much design plays into it. Only an EV would increase efficiency as speed approaches 0 mph at the low end IMO. Experiment.


#4

How much gasoline could the whole country save if we would all slow down to 65? I wonder what it costs per mile to run one of those big 18 wheelers. I hate driving on the interstae, but I must do it to get to work.


#5

Driving slower means that your engine is burning less gas for a LONGER PERIOD OF TIME for the same trip from point A to point B. No actual fuel savings for the total trip.


#6

New math?


#7

I agree that one of the most important safety factors in freeway travel is getting “everyone” to travel at the same speed. Unfortunately, the type “A’s” will almost always travel faster than the posted speed limit, be it 55 or 75 mph. These guys and gals just don’t like to be passed. “Turbulance” will always be there.


#8

Huh…that logic means that if you travel infinitely fast, you’ll use little or no gas. Type “A” logic. I like it. Start your engines; it’s Indy time to save gas.


#9

In general “everyone” will drive at an appropriate speed for the road and the conditions. On most (non-urban) highways that speed is in the 70-75 mph range, in urban areas the highway speed is usually more like 60-65. This speed has nothing to do with the posted limits. I normally don’t even know what the posted limits are when I’m driving in a strange area, I just try to drive at about the average speed of the traffic. That is the safest speed, and you have very little chance of getting a speeding ticket if you are not one of the fastest (or erratic) drivers.


#10

Nope, just the reallity that people don’t notice until you make the same trip over and over again. Now, this isn’t neccessarily true through all mph but think about it. The faster car gets to destination sooner and turns off the engine no longer burning fuel at all. The slower car is not there yet still burning fuel for fifteen minutes more ! MPG for MPH is directly relative to TIME spent for the equivilant trip.


#11

Not even close, the important parameter is not the time that the engine operates but the total amount of energy required to get the vehicle from one place to another. Traveling at higher speeds requires more energy due to higher wind resistance, higher rolling resistance, higher internal resistance, etc.

Another way to think of this is in terms of the number of engine rotations; driving 50 miles in high gear requires the same number of engine revolutions regardless of speed. Driving at higher speed will require more fuel per revolution.


#12

Proved it to myself many times. Gallup-Albuquerque-Gallup trip. Same trip, same truck, same fuel comsumption 60 mph vs speed limit of 75 mph.


#13

Your logic is baffling. Go back to school. The current standard for mileage is calculated by MPG. For instance, last time I drove on an out of town trip (500 miles), I maintained a speed of about 80 mph. My mileage was 19 MPG. That means, I used 26.3 gallons of fuel to get there. This was confirmed, because I had to fill up at 350 miles for 18 gals of a 21 gallon tank.

On vacation (no time requirements), I took the same trip with the cruise control on 60 mph. I was getting 23 MPG. This was confirmed, because I had to stop for fuel less than an hour away from my destination, and, at 450 miles traveled, I filled up 19 gals. I used 21.7 gallons.

If you can’t handle to occasional car driving 60 mph in the right hand lane, then you can kiss by rear. Please do, cause I could use the insurance settlement.


#14

This subject-matter thread gets started every few weeks. It always gets long and nasty.

In the '70s Jimmy Carter (via the Highway Department threatening to withhold federal funds) extorted all the states to reduce their speed limits to 55 mph. It was a joke. Cars and highways were simply designed to go faster than that comfortably and safely.

It wouldn’t work now either.


#15

That’s spot on, Craig. To Ken Green: Take my car, 60 mph = 2780 rpm = 166800 for a distance of 60 miles in 1 hour. Then, lets say, 30 mph. 30 mph = 1390 rpm = 83400 for a distance of 30 miles in one hour. That means 2 hours for a distance of 60 miles which results in 2 x 83400 = 166800. Now you can calculate on minor things like what Craig mentioned and see how much gas You’ll save.

That makes me think. If my engine had been driven all of its 170000 miles on a highway in fifth gear, then it would have done 472.600.000 revolutions and add to that the time spent on acceleration and idle time. Any higher numbers out there?. There must be.


#16

Comfortably and safely, yes, but not at peak fuel economy. Maximum fuel economy tends to occur at somewhat BELOW 55.


#17

As long as you’re buying the fuel, do whatever you think works best.


#18

You are correct; and if I cared about fuel economy I would drive much slower, and I would drive a vehicle that weighed half as much. If the cost of fuel ever gets up to a reasonable level, many people will start driving more slowly in more efficient vehicles. At the moment, there is very little incentive to do either.


#19

Understood. But the OP is only asking about fuel economy.


#20

I’ll bet your trips at 60 MPH involved a lot of traffic. Slowing down and accelerating back to 60 would eat up any gas savings vs. driving a steady 75 MPH.