1. ## MPG: Speed vs. Time

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.

2. ## Re: MPG: Speed vs. Time

cool a topic that involves math...not even goin try...

3. ## Re: MPG: Speed vs. Time

you won't have the same 20 mpg cause the engine is using more gas becuase of the excess spinning.... think of it like who will use more gas a person running 2300 rpms at 60 in 4th or a person runnin 1500rpms in 5th going 60 both going 200 miles

4. ## Re: MPG: Speed vs. Time

I know that. The question is here, do you still burn the same TOTAL amount of gas. I'm not saying this is true, but this is where the point is always made:

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?

I shouldn't have said anything about the 20mpg until later. I started this post in 2 other forums and everyone says something about the rpms.

5. ## Re: MPG: Speed vs. Time

Very good subject. Suscribed.

6. ## Re: MPG: Speed vs. Time

even better for ya.... given a distance of 100ft.... if a car is going thru that set distance of 100 ft with the rpms at 1500 doing 55 it will take him more time to clear it, but he will use less gas than a car doing 70 @2000rpms, the car going 5...............ahhh **** it it has to do with more than i can back up jus ttherory( i know t is right just can't explain it in detail)

7. ## Re: MPG: Speed vs. Time

i had aready started the post.......u can't just thro out the rpm's thou, becuase it is like an importat variable....more rpm's more gas...also it may have something to deal with the load that is on the engine...what other boards didyouplace this on??

8. ## Re: MPG: Speed vs. Time

This is something for the Myth Busters.

9. ## Re: MPG: Speed vs. Time

Originally Posted by TwistedMovistar
i had aready started the post.......u can't just thro out the rpm's thou, becuase it is like an importat variable....more rpm's more gas...also it may have something to deal with the load that is on the engine...what other boards didyouplace this on??

So that mean's on sunday when i went long driving back home from a competition i was going up this steep *** hill on the freeway. I was lagging so i gassed it and hit around 4rpm constant. That means i was wasting alot of gas huh?

dante

10. ## Re: MPG: Speed vs. Time

I think it would ultimately it depends on the distance driven. In theory this may hold true under ideal or certain circumstances, which you may neve actually encounter in real life.

For Example: Driving X distance @ Y speed burns Z Gas

You can change the variables and still burn the same amount of gas, but the distance driven on any given trip is, for the most part a constant. So under certain circumstances you may be right, but I am willing to bet that most of the time, driving a little slower is going to benefit gas consumption the best.

11. ## Re: MPG: Speed vs. Time

Originally Posted by TwistedMovistar
i had aready started the post.......u can't just thro out the rpm's thou, becuase it is like an importat variable....more rpm's more gas...also it may have something to deal with the load that is on the engine...what other boards didyouplace this on??
Well, the reason I said for now to forget rpm's is because that's not of concern for this post. I think everyone knows the more rpms' you use the more gas you consume. Which is the reason I come off cruise control on hills and accelerate myself.

I'm really wanting to get this down to a constant speed vs. time vs. mpg issue.

8thcivic.com/forum
sounddomain.com/forum

12. ## Re: MPG: Speed vs. Time

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

it makes no difference that you are there faster.
period.

13. ## Re: MPG: Speed vs. Time

Originally Posted by mikeyboc
I think it would ultimately it depends on the distance driven. In theory this may hold true under ideal or certain circumstances, which you may neve actually encounter in real life.

For Example: Driving X distance @ Y speed burns Z Gas

You can change the variables and still burn the same amount of gas, but the distance driven on any given trip is, for the most part a constant. So under certain circumstances you may be right, but I am willing to bet that most of the time, driving a little slower is going to benefit gas consumption the best.
I agree with you. I'm not trying to convince anyone of this. It's just something that I've wondered for a long time. And anytime I bring it up noone ever has a true explanation of why it wouldn't be correct. I'm in aerospace engineering...maybe I should talk to one of my professors about doing this as an experiment. I was thinking this might be able to be done in a garage (where they do engine tests and etc) but I'd also like to have drag factored in this as well, since it's the most prominent issue in mpg at high speeds.

14. ## Re: MPG: Speed vs. Time

You could test this yourself.

15. ## Re: MPG: Speed vs. Time

Originally Posted by GrayMatter4tw
i make a 500 mile trip a bunch of times every year and half is 80mph and half is 65.

250 miles @ 80mph
3.125 hours 16mpg 16.625gallons

250 miles @ 65mph
3.85 hours 21mpg 11.9gallons

it makes no difference that you are there faster.
period.
Nice. Real Numbers.
Was this constant speed (no engine revs, speed increases/reductions, cruise control, etc)?

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