MPG Stupid?



Just read a good article which recommends a new method of measuring fuel efficiency. Which saves more gasoline, going from 10 to 20 mpg, or going from 33 to 50 mpg?

If you’re like most,you picked the second one. But, in fact, that’s backwards. Over any given mileage, replacing a 10-mpg vehicle with one that gets 20 mpg saves five times the gasoline that replacing a 33-mpg vehicle with one that gets 50 does.

You can read more about it here:



Yep, Europe does it right by listing consumption (liters/100 km, or something like that).


Yes, those complex mathematical operations like division and ratios seem to be beyond comprehension for the majority of people. Like this gem:

Hey, this is 90% off, how much is that? Gee, I don’t know but 50% is half and this is way more than that!

While I agree that we seem to cling to antiquated systems in this country, catering to this level of ignorance is astounding.


Honestly, I don’t think either is better than the other. Both are measurements of how efficiently a vehicle uses gas. Whether it’s done in volume divided by distance (litres/100 km) or miles per gallon, it still “rates” how efficient the vehicle is gaswise.

The example given chose numbers designed to confuse, selected to demonstrate that care needs to be taken when playing with numbers, but in reality a person driving a 50 mpg vehicle is going to use less gas than a person driving a 20 mpg vehicle no matter how you play the numbers.

This illustration to me is like politispeak: if the labor force added 10,000 new jobs but lost 25,000 of the old jobs. is that a net gain? Nope. But the general media will say “labor force adds 10,000 new jobs”.

All the article points out to me is…be careful how you interpret what you read.

And beware of ethnocentrism.


My problem with mpgs is that some folks seem to think a 5 mpg change is equally important, whether going from 15 to 20 mpg (big change) or 35 to 40 mpg (very small change). The former would save 333 gallons over 20,000 miles, the latter only 71 gallons.


Interesting, but at what cost? Let’s say I replace my old pickup (10 mpg) for an American sedan (20 MPG) and it costs an additional $10k. Or, I replace my Honda (33 MPG) for a hybrid or TDi (50 MPG) for $30k. An important missing variable is total miles driven per year. And lastly, depreciation can far outweigh fuel cost in total life time per-mile cost. MPG (or l/100 km) is just one of the total cost factors.



This is something I have been saying for a long time.

Written by me on 11/16/2008 7:48:23 PM:

Keep in mind that measuring miles per gallon can give you deceptive results. You are really better off measuring gallons per mile, or gallons per 10,000 miles. An increase from 30 MPG to 40 MPG will save 83 gallons per 10,000 miles, while an increase from 10 MPG to 12 MPG will save 167 gallons per 10,000 miles.*

The point of this exercise is to point out where we should be focusing our efforts to improve fuel economy. We can get more bang for our buck by improving a few MPGs on a large vehicle than we can the same MPGs on a small light weight vehicle.


Honestly, in the bigger picture I don’t think it matters. If more people bought cars that got more MPGs consumption would drop. How one measures the consumption does not affect the consumption. Confusing the issue by changing he measuring standard would accomplish nothing but to confuse the buying public.

If we really wanted to refocus our efforts, I’m sure there are better areas to focus on. For example, the billions spent on the farm subsidies to support ethanol production plus the billions spent on idiotic programs like Cash For Clunkers, could be invested in supporting the development of a recharging infrastructure to extend the range of EVs, and supporting technology to develop EVs. Companys like Tesla would be a better investment of some of those billions. 50% subsidized purchases of EVs would be a better investment.

It’s clear that we need to refocus our efforts, but refocusing them on the measurement method accomplishes no reduction in consumption. A given vehicle on a given trip will use whatever it will use, whether measured in MPG or Parsnips per Fathom.