Gallons per mile, not MPG

WickedLou9 · 07-03-2008, 03:20 PM

Something interessting I learned the other day.

MPG is a misleading figure. Here is what I mean

Lets say we have 2 people

Sally drives a ford Explorer. She gets 20mpg.

Bill drives an Accord, he gets 30mpg

Bill and Sally are both angry about high gas prices so they decide to buy new cars.
Sally gets a v-6 Ford Fusion. She now gets 25mpg.
Bill gets a Honda Civic. He now gets 35mpg

Both Sally and Bill drive about 400 miles a week.
Both drivers experienced an increase of 5 mpg after thier new purchase.

However Bill soon discovers that he has been a dolt.

Sally has saved an average of 16 dollars per week or 832 dollars per year.
Bill saves less than half of that. He saves only 7.62 per week or about 396 dollars per year.

It's true that Bill pays less for fuel than sally, but Sally's increase of 5mpg had a much bigger benefit than Bills 5mpg.

The moral of the story is that if you drive an SUV or something that gets 18-20mpg, even a modest increase in fuel economy has big benefits.
If you already get 25-30 mpg... buying a new car really won't save you that much money. The incremental cost benefit of switching from something like a Civic to something like a Prius is minimal. Don't bother.

WickedLou9 · 07-03-2008, 04:02 PM

I'm really going to dork it up. Check out this chart I made in Excel. It really illustrates the issue well.

7960 · 07-03-2008, 04:10 PM

it's incremental gains, law of diminishing returns..........is this news?

Phantom · 07-03-2008, 04:10 PM

common sense?

WickedLou9 · 07-03-2008, 04:29 PM

Originally Posted by Phantom

common sense?

Not really. Most people think MPG is MPG. When you are comparing cars you just look at that one number. If you are looking at a large SUV or pickup truck, 1 or 2 MPG differece actually makes a big difference. When you get to something like a Civic 1 or 2 MPG is almost irrelevant.

So the point was that if you look at the cars "gallons per mile" rating you would see this hyperbolic curve where as if you just look at MPG, the graph is linear.

motivez · 07-03-2008, 05:51 PM

I think it's useful for a lot of people, I was actually talking to someone the other day who wasn't sure whether or not to buy a new car.. they didn't really know how to do any kind of cost/benefit analysis (...), I'm going to link this to them

6SpeedTA95 · 07-03-2008, 07:34 PM

Umm yeah thats called basic math

If you get 20 mpg and get 25 with your new car thats a 25% gain in mileage. If you got 30 mpg and get 35 its only a 16.6% increase in mileage...

nbiggershaft · 07-03-2008, 07:57 PM

They should stop paying me in dollars per hour and switch it over to hours per dollar. I don't want to get confused about a 5 dollar raise

Simius · 07-04-2008, 12:53 AM

Originally Posted by nbiggershaft

They should stop paying me in dollars per hour and switch it over to hours per dollar. I don't want to get confused about a 5 dollar raise

You can work for me for a 5 hour raise.

wait... wat...

WickedLou9 · 07-04-2008, 08:45 AM

Originally Posted by 6SpeedTA95

Umm yeah thats called basic math

If you get 20 mpg and get 25 with your new car thats a 25% gain in mileage. If you got 30 mpg and get 35 its only a 16.6% increase in mileage...

You give the general public too much credit.

lew · 07-04-2008, 10:03 AM

You guys really do give the general public too much credit.

I'd imagine something like 95% of the population doesn't understand this.

6SpeedTA95 · 07-04-2008, 11:32 AM

Originally Posted by lew

You guys really do give the general public too much credit.

I'd imagine something like 95% of the population doesn't understand this.

My car gets 40mpg and I'm going to spend 22k on a prius because it gets 43mpg! I win!

David Octavius · 07-04-2008, 07:08 PM

Not everything needs to boil down to marginal this or percentage that, sometimes people do things because it makes them feel good or maybe its just that they need a new car anyway so might as well get one with a higher MPG. I don't understand all this elitist crap spewing in this thread making fun of the public. To read this thread is to see an utter lack of understanding and a huge disconnect with you guys and the public at large.

Ardentfrost · 07-04-2008, 07:20 PM

Originally Posted by David Octavius

Not everything needs to boil down to marginal this or percentage that, sometimes people do things because it makes them feel good or maybe its just that they need a new car anyway so might as well get one with a higher MPG. I don't understand all this elitist crap spewing in this thread making fun of the public. To read this thread is to see an utter lack of understanding and a huge disconnect with you guys and the public at large.

You're describing the irrationality of the public. FEELING good does NOT mean it's ACTUALLY good. Recycling is a great example of this.

David Octavius · 07-04-2008, 07:37 PM

Originally Posted by Ardentfrost

You're describing the irrationality of the public. FEELING good does NOT mean it's ACTUALLY good. Recycling is a great example of this.

Irrationality is part of human nature, we are all irrational at one point or another. Trying to deride people for it only shows your own irrationality - its NOT the proper way to go about things.

Dispatcher · 07-04-2008, 07:49 PM

Originally Posted by David Octavius

Irrationality is part of human nature, we are all irrational at one point or another. Trying to deride people for it only shows your own irrationality - its NOT the proper way to go about things.

people are not irrational...they are insane. As my Grandmother used to say, "All the world is crazy but thee and me, and thou art a little whacko"

7960 · 07-06-2008, 11:20 PM

Originally Posted by WickedLou9

You give the general public too much credit.

and yet you expect them to understand the significance of your hyperbolic curve?

7960 · 07-06-2008, 11:21 PM

Originally Posted by Ardentfrost

You're describing the irrationality of the public. FEELING good does NOT mean it's ACTUALLY good. Recycling is a great example of this.

did you just say recycling is not good?

Ardentfrost · 07-07-2008, 08:26 AM

Originally Posted by 7960

did you just say recycling is not good?

For most things, recycling is not good. Not for the environment, not economically, and the "landfill benefits" are far overstated.

7960 · 07-07-2008, 08:30 AM

Originally Posted by Ardentfrost

For most things, recycling is not good. Not for the environment, not economically, and the "landfill benefits" are far overstated.

and you're going to leave it at that?

no explanation, no link to a story, no "I heard..........."

??