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MPG versus GPC
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Author:  Pat Dawson [ Fri Feb 27, 2009 4:47 am ]
Post subject:  MPG versus GPC
Think about this:

For every 100 miles driven, if I choose a vehicle that gets 15 mpg over one that gets 14 mpg, I would save the same amount of fuel as someone who chooses a vehicle that gets 50 mpg over one that gets 40 mpg.

Obviously, the 15 mpg vehicle would use more fuel than the 50 mpg vehicle, that's not the point.

It would be more useful for consumers to see GPC (Gallons per 100 miles)on the sticker instead of MPG especially as we are in an era where cars are achieving 40, 45 ,50, even 60 mpg.

So in our slanted world those who can get 20 or 22 mpg are really saving fuel over ones that are only achieving 16 or 17 mpg.

Say you tweaked your slant for economy and increased from 16 mpg to 22 mpg. If you decided you needed to park the 22 mpg slant for a more modern, more efficient car and you wanted to save the same amount of fuel you saved in your effort to get from 16 mpg to 22 mpg, then you would have to buy a car that achieves almost 38 mpg, an increase of 16 mpg.

I didn't come with this idea, I read it in a car mag. I couldn't see it until I did some conversions and graphed it out.

Comments?
Author:  bbbbbb9 [ Fri Feb 27, 2009 5:58 am ]
Post subject: 
Ummmmmmmmmmmmmm, no.

14mpg and you drive 100 miles you use 7.14 gallons of gas

15mpg and you drive 100 miles yu use 6.67 gallons of gas

40mpg and you drive 100 miles you use 2.5 gallons of gas

50mpg and you drive 100 miles you use 2 gallons of gas

Not seeing your point at all.
Author:  dakight [ Fri Feb 27, 2009 6:13 am ]
Post subject: 
The point is that going from 14 to 15 mpg saves about 1/2 gallon every hundred miles. Going from 40 mpg to 50 mpg saves about 1/2 gallon every hundred miles. I'm not altogether sure why that is important, except that as mpg gets higher there are diminishing returns for incremental increases and other factors might become more important than the mpg figure.
Author:  bbbbbb9 [ Fri Feb 27, 2009 6:24 am ]
Post subject: 
But the 14-15 mpg range vs the 40-50 mpg range is what, a 12-14 gallon difference?

Not sure how comparing those have any significant point other than to write an article.
Author:  bbbbbb9 [ Fri Feb 27, 2009 6:26 am ]
Post subject: 
Quote:
The point is that going from 14 to 15 mpg saves about 1/2 gallon every hundred miles. Going from 40 mpg to 50 mpg saves about 1/2 gallon every hundred miles. I'm not altogether sure why that is important, except that as mpg gets higher there are diminishing returns for incremental increases and other factors might become more important than the mpg figure.
It's a simple "Economy of Scale" and very hard to argue with. Over the life of the vehicle there is a significant savings between 50 mpg and 40 mpg
Author:  SlantSixDan [ Fri Feb 27, 2009 6:53 am ]
Post subject: 
The point is a valid one. Human beings, except those math whizzes you can see occasionally on television, are very poorly equipped to understand numbers. We can work with 'em to varying degrees (mental math) but it is very difficult for us to understand them without cognitive bias getting in the way and screwing us up. An example of such bias: We'll drive across town to save $20 on a $175 microwave oven, but not to save the same $20 on a $1400 television set (leaving aside the question of who the hell needs a $1400 television set). Another example: we'll say "Yes" to the car priced at $14,992 but "No" to the car priced at $15,009 (grand total difference of seventeen whole dollars). Another example: Subjects in experiments will do something to "win 300 cents" that they won't do to "win three dollars". It's just the way our brains are built and wired. 

Expressing fuel consumption (how much fuel it takes to go a realistically-large particular distance) rather than fuel economy (how far you can go on a small particular unit of fuel) helps people get a reasonable and realistic mental grasp of the operating costs for whatever vehicle they're driving (or, more importantly, thinking of buying). Fuel consumption illustrates the point that the most substantial efficiency gains are at the low-efficiency end of the market (trucks, SUVs, Hemi 300Cs, etc.) A 50% efficiency gain in a 10 mpg vehicle saves MUCH more money than a 50% efficiency gain in a 30 mpg vehicle. So not only is the improvement from 10 to 15 mpg much more financially significant than the improvement 20 to 25 (the same arithmetic difference) but it's also more
significant so than going from 20 to 30 (the same relative improvement).

Expressing fuel consumption also makes it a lot easier to figure out fuel costs on the fly in your head before you get in the car. Sure, anyone can sit down with a pencil and paper (or a calculator) and figure out how much fuel it takes to go "X" distance in a vehicle that gets "Y" miles per gallon, but that is a calculation to transform fuel economy into fuel consumption. Better just to express consumption right in the open.

Watch this-

I have a car that takes 11 L/100 km (11 litres of fuel burned to travel 100 km). Okay, fuel is currently about 80¢/litre, so those 11 litres will cost me roughly $9, so it's nine bucks in fuel to go 100 km, and I drive about 400 km a week, so my fuel costs are $36 a week. If I want to drive to Hamilton and back, that's 120 km, which will cost me about $10.50 in fuel. Makes it really easy to compare to train fare, bus fare, etc. If my car got 9 L/100 km, those 100 km would cost me $7.20, my weekly 400 km would cost me $28.80, and the trip to Hamilton would cost me about $8.60. All in my head, no paper, no fingers, no calculators, and I am not a math whiz.

Now watch this:

I have a car that gets 17 mpg. Fuel is $2.64/gallon. So that's 17 miles per $2.64. I drive about 250 miles a week, so 250 divided by 17...um...hang on, I'll grab a calculator. Oops, no more quick mental calculations close enough to accuracy to be useful.

The article (and Pat Dawson) have a valid point.
Author:  bbbbbb9 [ Fri Feb 27, 2009 7:46 am ]
Post subject: 
Hmmmmmmmmmm, so the point is to continue the dumbing down of Americans?

Listen I love my slant six and hopefully (one day soon) I'll be driving it once or twice a week. But my 35 mpg car is my daily driver.

So the point is to make it easier to understand? I think it's propaganda really. No offense to Pat here at all.

It's an article from a car magazine that is aimed (I'm assuming here for sure) at an audience who would rather have their consumption habits validated than to educate themselves.

IMHO

And I am not trying to start an argument here
Author:  SlantSixDan [ Fri Feb 27, 2009 8:11 am ]
Post subject: 
Quote:
Hmmmmmmmmmm, so the point is to continue the dumbing down of Americans?
Uh...no, the point is to provide usable, useful information. You want your weather forecast in Kelvins rather than degrees Fahrenheit or Celsius? How 'bout your maps, do you want 'em scaled in furlongs instead of miles or kilometres? Of course you don't. You could use any of those kinds of presentations, but it would be more difficult to get the information to a point of utility and usability. Why not just present the information in useful form to begin with? That's not "dumbing down", by any stretch of the imagination…except perhaps in the stunted imaginations of perpetually-angry AM-talk-radio hosts.
Author:  bbbbbb9 [ Fri Feb 27, 2009 8:28 am ]
Post subject: 
Quote:
Quote:
Hmmmmmmmmmm, so the point is to continue the dumbing down of Americans?
Uh...no, the point is to provide usable, useful information. You want your weather forecast in Kelvins rather than degrees Fahrenheit or Celsius? How 'bout your maps, do you want 'em scaled in furlongs instead of miles or kilometres? Of course you don't. You could use any of those kinds of presentations, but it would be more difficult to get the information to a point of utility and usability. Why not just present the information in useful form to begin with? That's not "dumbing down", by any stretch of the imagination…except perhaps in the stunted imaginations of perpetually-angry AM-talk-radio hosts.
Wow, I've never been compared to an AM radio host before.

Seriously Dan, you can't see MY POINT???
Author:  SlantSixDan [ Fri Feb 27, 2009 8:41 am ]
Post subject: 
No. Usually you're pretty thoughtful, so I don't think you're just jerking your knee, I think you're just still having trouble understanding the idea. You're welcome to your opinion, of course, and if you work to understand the idea and think about it and wind up disagreeing, that's entirely respectable, but you are not entitled to be left alone if you champion an uninformed opinion.
Author:  Pat Dawson [ Tue Mar 03, 2009 6:23 am ]
Post subject: 
Interesting comments. bbbbbb9, you were almost there, Dakight finished the math.

7.14 - 6.67 = .47 fuel savings per 100 miles compare 15 to 14 mpg

2.5 - 2.0 = .50 (almost) same fuel savings per 100 miles 50 to 40 mpg


SSD analyzed it completely. GPC is a better method than MPG to compare efficiency when shopping for a vehicle.

bbbbbb9, take some graph paper, calculate more MPG to GPC points and graph it out. Watch the curve. That was my "aha" moment. The scary part is that the more efficiency we achieve the less it matters and that spells the end for fossil fueled vehicles at some point if we are to believe that we are coming to an end to economically viable new fossil fuel sources.


Now, if I could just convince you of this (much tougher sell):

If you have a rear-view and left and right side mirrors and you can see cars behind you in your side view mirrors you are not adjusting your mirrors properly. I know - you've been doing it your way all of your life - it's still wrong.

I learned this from my insurance company. Took some getting used to (cause I was doing it wrong too) but since I have made the adjustment I have never unknowingly cut anyone off nor do I have turn my head to "double-check") when changing lanes.

A rear view mirror is just that - for rear view. Adjust your side mirrors so that cars coming up in the left or right side of you are visible in the side view mirror until your peripheral vision takes over. When no cars are present you'll be looking at median strips or guard rails and that's what is difficult to get used to. PS - it doesn't work if you can't see out the back (example: semi truck with trailer)
Author:  bbbbbb9 [ Tue Mar 03, 2009 6:37 am ]
Post subject: 
Woudn't you have to adjust them while driving? Or at least have another car with you in a large parking lot?
Author:  SlantSixDan [ Tue Mar 03, 2009 7:12 am ]
Post subject: 
PD's right again: most of us adjust our sideview mirrors incorrectly (much too close to the vehicle and with way too much overlap with the rearview). They should be adjusted to give just enough overlap in view to provide continuity, so you don't lose your spatial orientation when going from one mirror to another and aren't forced to jump back and forth from rearview to sideview trying to piece together a complete visual field. The inner edge of the sideview's field should just barely include your own vehicle when you move your head sideways in the direction of that mirror.

This is both a tougher order and a more critical one with smaller sideview mirrors...like the ones on most of our cars. :-(
Author:  bbbbbb9 [ Tue Mar 03, 2009 9:22 am ]
Post subject: 
Quote:
PD's right again: most of us adjust our sideview mirrors incorrectly (much too close to the vehicle and with way too much overlap with the rearview). They should be adjusted to give just enough overlap in view to provide continuity, so you don't lose your spatial orientation when going from one mirror to another and aren't forced to jump back and forth from rearview to sideview trying to piece together a complete visual field. The inner edge of the sideview's field should just barely include your own vehicle when you move your head sideways in the direction of that mirror.

This is both a tougher order and a more critical one with smaller sideview mirrors...like the ones on most of our cars. :-(
Having worked construction and pulled numerous sizes of trailers this is actually how I always adjust my side mirrors. Just the slightest part of my vehicle in the field of view
Author:  Wizard [ Tue Mar 03, 2009 9:30 am ]
Post subject: 
Thank you!!

That is what I do with my caravan's side mirrors also. Stock side mirrors are small, but I have CV mirrors in my pile of parts that are bigger, just need good time to put them on.

Cheers, Wizard
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