What's the Deal...?

The OP lives in Canada so you'd think l/100 km would be just the thing.

Quentin - you gave an excellent explanation.

 

Why did you start this thread complaining about the proliferation of the gal/100mi standard?

BTW, I'm not saying that you or I can't do the math. I'm saying that people often don't actually do the math (see people claiming that the next gen Prius better get 60mpg or they aren't buying). If we ultimately want to minimize the fuel used and money spent, using an efficiency standard where higher is better is sort of silly. I can't think of a ton of other efficiency units that use the volume of energy in the denominator.

 

Another example comes from extending this observation:

... this is the same amount of fuel difference as a Prius bouncing between 35 MPG and 50 MPG. And I cannot count how many times PC posters have seen narrower swings within this range as being a catastrophe.

Efficiency losses from rain and snow and AC use also get unreasonably magnified in a Prius, and hidden on the SUV end, by the MPG scale. The Gal/100mi scale keeps these losses in equally scaled perspective regardless of the vehicle.

The US MPG scale also cost me real money, thousands of dollars, during the Cash For Clunkers deal. A little arithmetic revealed that the incentive was structured around trades that saved at least 1 Gal/100 miles for the lower incentive, and 2 Gal/100 miles for the higher incentive. Then it was translated to an MPG basis, and several limits artificially added to keep it simple enough for innumerate Americans to figure out. The result was that many truck & SUV owners making trades to newer trucks & SUVs that saved 1.0 gal/100 miles received a $3500 incentive, but my trade (from an already-efficient car for that era to a Prius) that saved more than twice as much fuel, 2.2 gal/100 miles, received nothing.

 

[emphasis added]

Speak for yourself.

 

LOL
Few people beat me in mental arithmetic, but dividing something into 235.2 is definitely out of my league too.

OTOH, memorizing that 6L/100km = 40 MPGus, and then calculating proportions mentally is pretty easy for a lot of people if they understand the idea. And to the point of the OP, as someone who has lived under multiple measuring systems I can say that the best approach is to simply not convert at all. Just learn the applicable range for daily use.

As an example, I know that 15c or less during an overcast day is unpleasantly cold for me unless I am active, and anything over 26C in the summer is unpleasantly hot outdoors out of the shade. When I moved to a farenheight country I found the corresponding values.

 

Try this:
3.9 is 0.8 less than 4.7
0.8 is a bit more* than 1/6th of 4.7

So the corresponding MPG is 50 + 1/6th of 50. The easy estimate is 59.

---
Or just estimate that every 0.1L/100km is a 2% change. That will lead to a result that is about 3% lower than actual.

*Corrected

 

I would memorize the same 4.7L/100km as 'EPA,' and then know that ~ every 0.5 change in L/100km is a 10% deviation. Since I know that 20% less fuel consumption than EPA is a pretty good target, I would shoot for 3.7L/100km

Conversions are a PITA. Percentages and fractions of a few key values is *so* much easier if a little inaccuracy is tolerated.

 

Well, I didn't say how many significant figures I normally keep, four is clearly excessive for this exercise. And from you other posts, I'd guess that you are much closer to this league than you suspect.

 

^^ Very few people use all that phrase to describe me.

 

Fun with numbers:
If you can tolerate using 234 as the unit conversion constant,
it is (not completely) factored to 3 * 6 * 13,
or perhaps even better, 4.5*4*13

Those numbers are pretty good jumping off points for other values.

 

Correct, 5 mpg represents a larger percentage over 15 MPG than over the 35 MPG sedan... It's simply percentages.

However, at least the way L/100km works out as fuel economy gets better, the number gets smaller. How many people really grasp the difference between 4.7 and 4.3... Those two numbers are REALLY similar, so surely they yield really similar fuel economy, right?

Metric or standard, I don't really care... But unit/distance is wonky.

 

Irrational.

 

I like Pi.

 

Well ... it's kinda easy if it's small numbers ... like 50 MPG is 2 Gal/100 Mile; 25 MPG is 4 Gal/100 Mile, so that's easy to cowvert. But numbers like 37.2 MPG or 2.7 Gal/100 Mile is a bit harder.

 

So at least you got me thinking of how much money I will be saving ...

It's funny I picked 37.2 ... 37.5 is 3 Gal/mi.

Here is a "savings" chart at different MPG between my XB and an estimated MPG on my prius


Mi / Yr $ / Gal Old MPG New MPG
25000 2 25 45
Old $/yr Cost=> 2000 1111.11 <= New $/yr Cost
-888.89 <=Savings

25000 2.5 25 45
Old $/yr Cost=> 2500 1388.888889 <= New $/yr Cost
-1111.11 <=Savings

25000 3 25 45
Old $/yr Cost=> 3000 1666.666667 <= New $/yr Cost
-1333.33 <=Savings

25000 4 25 45
Old $/yr Cost=> 4000 2222.222222 <= New $/yr Cost
-1777.79 <=Savings

25000 5 25 45
Old $/yr Cost=> 5000 2777.777778 <= New $/yr Cost
-2222.22 <=Savings