MPG: Speed vs. Time

[bikinpunk]

I've had this talk with alot of people over the course of my driving years, and I'm sure some of you have wondered this as well.

If you go slow, everyone knows that you use less gas than going fast. The faster you go the more gas you burn. I've even read that you add the equivalent of 20 cents per gallon for each 5 miles per hour you drive over 60 mph.

That being said, if you're driving faster you get to your destination faster. So, my question is, are you consuming relatively the same amount of gas by going faster thus reaching your destination sooner? Or do you still lose gas by going faster? If you increase your speed you'll get to your destination quicker. So, the question is, is the speed vs. time vs. mpg relatively the same as it would be if you were going slower?

I'm making these numbers up unless I have an equation next to it:
Say you burn 20 mpg going 65. Your trip is 20 miles, so you burn ~ 1 gallon of gas. You make the trip in about 18 minutes, 30 seconds ( (20 miles/65 mph)*60 min/hour).

If you increase to 80 and make the trip in 15 minutes, then are you still consuming the same total amount of gas?

I realize lower rpm's burn less gas, but in terms of speed alone.

[GeezerSi]

It takes more energy to maintain a higher speed. It's been proven many times that a slower speed over the same distance saves energy. I know what your saying, but there's no way around it. Sorry.

[bikinpunk]

Okay, so are you burning less gas TOTAL at a lower speed than at a higher speed?

Don't say sorry, it's not like I've been arguing this as a truth. It's just something that always gets brought up when talking about gas and noone ever has a true explanation. Thought I could get some input from some people here.

I think speed vs. time would be exponential. Thus, the more speed (rpms whatever) you have the higher the gas expenditure is, but the quicker you get there. You're reaching your destination faster at a faster speed. So, are you burning the same total amount of gas at a faster speed as you would a slower speed but getting there in a longer period of time?

[pickle430]

if that is the case how come when i do 79 on the free way i use less gas than going 65. i do 79 because 80+ is vtec 3500RPM. so im saving gas by not driving in vtec

Edit: I may be wrong but this is just my experence

[JeShUa]

Any mileage over 55mph will have a significant decrease in mpg.

You just get less miles on your odometer at the end of your tank, thus spending the same amount of money for less miles, in the end spending more per mile and getting a worse mpg.

[bikinpunk]

From another board's post:

i make a 500 mile trip a bunch of times every year and half is 80mph and half is 65.

250 miles @ 80mph
3.12hours 16mpg 16.6gallons

250 miles @ 65mph
3.85hours 21mpg 11.9gallons

cruise control the whole way
65mph part has maybe 4 or 5 slowdowns due to going through towns but no stops.
the 80mph part is a straight shot though on I-75

[sonitex]

When I had the Ridgeline, prior to Katrina, I enjoyed having my first pick up truck, in the highest form (best truck of the year). I was averaging 14-15 mpg. After Katrina, I started to count the nickles and dimes that went into our gas tanks. My Wife's CRV was only averaging 23 mpg (90% hwy). I then realized that I really did not need a truck to commute back and forth to work (6 miles one way, back roads).

Now, my wife drives the 06 ABM EX Coupe W/ ATM, and avg 35 mpg. She feels that she is driving a caddy.
Now I drive the 06 ASM Si. and avg 25 mpg. I no longer count the nickles and dimes for one reason only, we both are sooooo happy driving our cars. I like the idea of being able to drive my Si like a sports car I could never afford before. So, my response to this thread? Could care less.

[bikinpunk]

[tronvex]

One thing that I like about the R18 SOHC is that when you get cruiseing speed it lower the amount of fuel it take in. Instead of being 1.8 liter it switch to 1.5 liter this way it conserv the fuel. But yeh I think at lower speed and lower rpm the car should be getting more mpg, I see the difference when I drive my car nice a easy and when my friend drive his car hard. He would have to gas up more. Here is a video link on the R18 explain about the engine...
http://world.honda.com/HDTV/news/2005-4050705a/

[HAQER]

That's like one of those...

If train A leaves cleveland 5pm and tain B leaves LA at 645 then how many apples does Johnny have?

[pickle430]

Originally Posted by HAQER

That's like one of those...

If train A leaves cleveland 5pm and tain B leaves LA at 645 then how many apples does Johnny have?

lol

[Doolie77]

Obviously, he has 4 apples. And the train engineer's name is Bob. All the answers are in the question if take the time to read deeply in to it. :P

[bhoy]

but now with better aerodynamics we could go faster before wind resistance becomes a factor to gas mileage

[8thgenuser]

Originally Posted by bikinpunk

I've had this talk with alot of people over the course of my driving years, and I'm sure some of you have wondered this as well.

If you go slow, everyone knows that you use less gas than going fast. The faster you go the more gas you burn. I've even read that you add the equivalent of 20 cents per gallon for each 5 miles per hour you drive over 60 mph.

That being said, if you're driving faster you get to your destination faster. So, my question is, are you consuming relatively the same amount of gas by going faster thus reaching your destination sooner? Or do you still lose gas by going faster? If you increase your speed you'll get to your destination quicker. So, the question is, is the speed vs. time vs. mpg relatively the same as it would be if you were going slower?

I'm making these numbers up unless I have an equation next to it:
Say you burn 20 mpg going 65. Your trip is 20 miles, so you burn ~ 1 gallon of gas. You make the trip in about 18 minutes, 30 seconds ( (20 miles/65 mph)*60 min/hour).

If you increase to 80 and make the trip in 15 minutes, then are you still consuming the same total amount of gas?

I realize lower rpm's burn less gas, but in terms of speed alone.

I think I understand the reasoning of your question. Basically, you're theory is that if you decrease your speed to increase your fuel economy, you're on the road for a longer period of time, thus increasing your gas usage, compared to driving at a higher speed with less fuel economy.

If we can assume that your fuel economy increase as you decrease speed and the total number of miles is the same, then the above theory doesn't hold water.

# of Gallons Dependent on Total Amount of Miles:

    x miles          x
---------------- =  --- gallons
y miles/gallon       y

# of Gallons Dependent on Time:

   x miles/hr       x
---------------- = --- gallons/hr
y miles/gallon      y


 x                           x*z
--- gallons/hr  * z hours = ----- gallons
 y                            y

Try the equations for your two cases. You'll see that the number of gallons used will be less if you increase your fuel economy by reducing your speed.

BTW, you'll need to assume some sort of MPG when you travel 80 miles in 15 minutes, otherwise, you won't be able to answer your question.

[6ft5inAllMan]

Here is a question. Does the fuel rail squirt the same amount of gas per cycle into the cylinders at all rpm's?

If you drive at 3000 rpm's will it consume half as much gas when compared to 6000 rpm's?

[yacoub]

Originally Posted by JeShUa

Any mileage over 55mph will have a significant decrease in mpg.

False. Maybe for the big heavy old un-aerodynamic cars of yester-year. Maybe also if the transmission doesn't have an overdrive gear with a lower than 1:1 ratio.

With the Civic's awesome coefficient of drag and decent overdrive gear, I get excellent gas mileage going ~65-70mph. I have mixed driving but when I'm on the highway I am cruising at 65-70mph and this is my gas mileage thus far:

Miles	   Gallons 	Miles per Gallon     Total Miles

311.0	   9.502	    32.730	     311.0
323.0	   10.155	    31.807	     634.0
318.0	   9.903	    32.111	     952.0
302.0	   9.060	    33.333	     1,254.0
321.0	   9.697	    33.103	     1,575.0
317.0	   9.343	    33.929	     1,892.0
306.0	   9.170	    33.370	     2,198.0
325.0	   9.612	    33.812	     2,523.0
312.0	   8.998	    34.674	     2,835.0
321.0	   10.003	    32.090	     3,156.0
236.0	   7.191	    32.819	     3,392.0
324.0	   9.830	    32.960	     3,716.0
323.0	   9.490	    34.036	     4,039.0
300.0	   9.229	    32.506	     4,339.0

This is a 2006 EX sedan automatic, with the AC on most of the time.

[claudeboi]

an easy answer is, try to imagine it at as a "parabola", when you pass a horizontal line through a parabola, it crosses TWO points right? now that explains the contradiction of lower speed longer time and higher speed shorter time.....but theres one point in the parabola that if you pass a horizontal lin it only passes through on point (the very top, or crest), now that is the optimum time and speed that you can save fuel and maximize time, in other words its optimized......if you understand calculus' concept of rates of change and optimization, this will shed the light