Drivers fooled by 'MPG illusion'

[skadistic]

But if I understood the article right, it's better to go from 10 to 20MPG than go from 25 to 50...

Its relatively better to each other. But its still as simple as 33 is better then 30 and 42 is better 40. The amount of betterness may be better when the % of betterness is applied to the lower numbers. You may get a bigger jump at lower numbers but at higher numbers you are already ahead of the game. I think the phrase is something about 'diminishing returns'.

 

[classical_hero]

The litre / 100 KM thing is done here, but I still see most people use MPG.

As to fuel efficiency, while the study is true, it misses the mark that the 50 mpg car is going to be cheaper to run than the 11 mpg SUV. Always. The amount saved by switching from a 10mpg SUV to an 11 mpg SUV might be more, but you still pay more over all than the guy in the Prius. Which is what matters to most people at the end of the day.

That is what we use here. I think it much better because generally we equate lower numbers as being better, so it is confusing to have a higher number as being a better efficient car.

 

[Cheezy the Wiz]

http://www.guardian.co.uk/environment/2008/jun/20/travelandtransport.carbonemissions




Way to go guys, I admit, I was fooled too.

SPF ratings for suntan lotion are similarly misleading. It pretty much levels off at about SPF 30 or so: higher SPF ratings are not a comparable improvement on SPF30.

 

[I'm Cleo!]

The point is that if your distance traveled is unchanged (which it usually is), and you choose to upgrade your 10 MPG car to a 20 MPG car, that upgrade will reduce your gasoline consumption more than if you upgrade your 25 MPG car to a 50 MPG car. That's it. It's not making any more claims than that.

Cleo

 

[Bamspeedy]

But that's the problem, Augurey, it isn't true.

This isn't about upgrading from a SUV to a hybrid, it's about when people have both and being forced to make a choice of upgrading one or the other (SUV to a more efficient SUV, or upgrading the compact to a hybrid).

Yeah, those are legitimate for that instance. I was calling foul on the ridiculous 10 to 11 vs 33 to 50 claim.

Half a gallon difference over 500 miles when he said they were the same?

How about going from 10 to 12 mpg vs going from 28 to 50mpg as being (almost) the exact same thing? Of course, people would want to go from 10mpg to 50, but that isn't what the report is about.

Anyways to sidetracked a bit here, I saw an ad in the paper a few weeks ago that advertised a new car and it posted 'Your monthly gas savings if you buy this car compared to your old car' and it showed a chart based on your current vehicle's mpg. I would have saved $69/month. But, considering right now I don't have a car payment because mine is paid for and I only have liability insurance since it is 11 years old, I am way better off financially to keep my truck.

 

[Mise]

Yeah, agreed Bamspeedy. If it was 35 instead of 33, the 10mpg vs 11mpg would win. It's a fairly trivial difference -- the thrust of the article is perfectly sound.

The article correctly highlights that switching from MPG to GPM would be a much more intuitive and straightforward measure.

 

[bhsup]

Yeah, agreed Bamspeedy. If it was 35 instead of 33, the 10mpg vs 11mpg would win. It's a fairly trivial difference -- the thrust of the article is perfectly sound.

Hardly. It's simple math. They utterly botched it and deserved to be called on it. And as you said, it is so trivial, they should not have even used that one as an example anyway.

 

[Phlegmak]

The article is bad. MPG is perfectly fine. What the article is complaining about is the "savings" difference of changing an X1 MPG car to X2 MPG car, vs. a Y1 MPG car to a Y2 MPG car. Talking about the relative "savings" in gasoline usage doesn't make much sense to me. A 50 MPG car is still more fuel efficient than a 49 MPG car or an 11 MPG car.

 

[Ayatollah So]

It's amazing how stupid people can be in some contexts, while being smart in others. I guess framing is everything. Forget mpg and gpm. How you word the question determines what answer most people will give you - on just about any subject whatsoever.

 

[Mise]

Hardly. It's simple math. They utterly botched it and deserved to be called on it. And as you said, it is so trivial, they should not have even used that one as an example anyway.

I think you misunderstand what I'm saying.

Lets use 35 vs 50 instead of 33 vs 50.

Over 500 miles, a 35mpg car uses 14.29 gallons. A 50mpg car uses 10 gallons, which is a saving of 4.29 gallons.

A 10mpg car would use 50 gallons, and an 11 mpg car would use (as you correctly calculated) 45.45 -- a saving of 4.55 gallons.

So you save more going from 10mpg -> 11mpg than you do from 35mpg -> 50mpg.

The difference between 33 and 35 is trivial. The thrust of the article, and the example given, is not. 10mpg vs 11mpg seems like a trivial difference, but it is more significant than 35mpg vs 50mpg.

 

[bhsup]

The difference between 33 and 35 is trivial. The thrust of the article, and the example given, is not. 10mpg vs 11mpg seems like a trivial difference, but it is more significant than 35mpg vs 50mpg.

But don't you see what you're doing there? You say 33 to 35 is trivial, which I more or less agree with you on. But suddenly when you are making the comparison, you change the 35 to 50, and 33 to 50 IS huge.

 

[Mise]

But don't you see what you're doing there? You say 33 to 35 is trivial, which I more or less agree with you on. But suddenly when you are making the comparison, you change the 35 to 50, and 33 to 50 IS huge.

No, it's not, and I never said it was . The difference is 0.86 gallons.

The comparison should be between 10mpg -> 11mpg and 35mpg -> 50mpg. Those jumps both represent pretty much the same savings, even though the difference between 35mpg and 50mpg looks like it should save a lot more.

 

[Phlegmak]

By the way, here are some GPMs:

10 MPG => 0.1 GPM
11 MPG => 0.09 GPM
25 MPG => 0.04 GPM
33 MPG => 0.0303 GPM
35 MPG => 0.0285 GPM
50 MPG => 0.02 GPM

Am I missing something here? I see no amazing trend here. The ONLY thing I see is the smaller changes when using GPM. And I still think that MPG is perfectly fine.

To make the calculations above, I simply took the reciprocal of MPG.

 

[mrt144]

the marginal decrease in fuel savings as cars become more efficient in fuel has what implications? that it's bad to try and maximize efficiency or the cost of doing so outweighs the benefit?

also the comparisons they make are stupid and are based on a false dichotomy.

 

[LucyDuke]

Innumeracy. Is anyone actually surprised?

Wah, math is hard.

 

[EdwardTking]

I think that the article is sound, but there is either a typo or an editor sexing it up.

While:

Likewise, replacing a car that does 10mpg with one that appears only slightly more efficient at 11mpg saves as much fuel as upgrading from a 33mpg car to a 50mpg car.

is, as VRWCAgent points out, incorrect.


Likewise, replacing a car that does 10mpg with one that appears only slightly more efficient at 12mpg saves as much fuel as upgrading from a 33mpg car to a 50mpg car.

and

Likewise, replacing a car that does 10mpg with one that appears only slightly more efficient at 11mpg saves nearly as much fuel as upgrading from a 33mpg car to a 50mpg car.

would be correct.

 

[Mise]

@Phlegmak: GPM scales linearly with the amount of petrol used. MPG scales inversely (reciprocally, as you say) with the amount of petrol used. Clearly, a linear scaling is preferable, since it's easier to get a feel for how much petrol you're going to save.

 

[Masquerouge]

I love where this thread is going

 

[bhsup]

@Phlegmak: GPM scales linearly with the amount of petrol used. MPG scales inversely (reciprocally, as you say) with the amount of petrol used. Clearly, a linear scaling is preferable, since it's easier to get a feel for how much petrol you're going to save.

Only if someone can't do basic math in their head...

 

[nivi]

Only if someone can't do basic math in their head...

Most people can't, especially when the math is just a bit counter intuitive.