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Why MPG is wrong: Measurement matters

by David Zatz, PhD

When fuel economy figures for the Hurricane-powered 2025 Ram 1500 showed up [story at Stellpower], some yawned while others were quite excited. One factor was whether people realized that 3 mpg is a yawn for cars already achieving 30 mpg, but quite important for trucks getting 15 mpg.

The problem is that miles per gallon (mpg) is not a linear measurement—it’s not a straight-line thing. Gallons per mile would be, but we don’t use that; neither does anyone else, mostly because very few countries use gallons. Instead, most of the world uses the truly-linear liters per 100 km—roughly, quarts per 62 miles. It’s clumsy to write, say, or abbreviate (L/100km), but it is linear and doesn’t cause us to get confused. Here is the source of the confusion with mpg:

MPG curve (vs l/100km

(If this curve looks lumpy, it’s because I only ran so many data points, and then used horizontal lines.)

Adding just one single mile per gallon (1 mpg) on a truck that averages 15 mpg (city) means 4 gallons per thousand miles—around 48 gallons per year. That doesn’t seem like much until you multiply by, say, 400,000 trucks sold in a year—19.2 million gallons of fuel. That’s an important mile per gallon.

My family’s Chrysler is rated at 19 city, 31 highway. A single 1 mpg increase in city driving saves 2.5 gallons of fuel per thousand miles; the same 1 mpg on the highway only saves 1 gallon per thousand miles. This is what comes of having the wrong number in the top of the equation!

Now, let’s look at the new Ram 1500. With the Hurricane engine, which is not a hybrid, it saves 3 mpg over the old non-hybrid Hemi. For illustration, we’ll see what taking, say, a Dodge Dart Aero from 40 mpg to 43 mpg would do. The answer is that the Aero would not do much—over a year, it would save 1.7 * 12 = 20.4 gallons of fuel, netting the owner around $62 in savings, and over maybe 60,000 sold, 1,224 gallons of fuel per year. But on a Ram 1500, the story is quite different! If we look at a city/surburban driver, we see 11.1 gallons of fuel saved per thousand miles—that’s around 133.2 gallons per year, or $400 at $3/gallon. Now multiply by the number of Rams sold in a year and you get into serious savings of money and fuel and pollution.

Gallons saved per year
  City Highway
Ram 1500 133.2 78
Dart Aero 36 20.4

If you multiply your Ram by its design lifespan of around 17 years—200,000 miles—that’s around $6,800, quite enough for maybe an extra repair or two. The gap is even bigger if you use the midgrade fuel required for the Hemi V8—because the Hurricane takes regular-grade fuel. It’s also obviously a higher number if gasoline prices rise above $3 per gallon; currently, in this area, they are around $3.30 for regular and $3.55 for midgrade. The 2,264 lifetime gallons multipled by $3.55 rather than $3 comes out to over $8,000.

Assumes Ram 1500 Hemi, non-hybrid, at 15 mpg city, 20 highway. Assumes Dodge Dart at roughly 30 city, 40 highway.

Here’s a chart so you can check the math and satisfy your curiosity. Yes, it might time to get a good tune on that old Fury III in your garage.

Savings per thousand miles
Rising 1 mpg Rising 3 mpg
10 9.1 10 23.1
15 4.2 15 11.1
20 2.4 20 6.5
25 1.5 25 4.3
30 1.1 30 3.0
35 0.8 35 2.3
40 0.6 40 1.7

The average car is driven around 12,000 miles per year, if you were curious as to the calculations for gallons saved per year. You can clearly see that as a vehicle gets higher and higher gas mileage, one (or three) miles per gallons means less. That also means that the biggest guzzlers in the Mopar fleet, which is to say the Wrangler, Gladiator, and Ram series, as well as the new Wagoneer, are in dire need of any improvements possible.

This is the comparison chart for the Ram 1500 with the two Hemi choices and with the Hurricane. Gas mileage with the V6 is completely unchanged from 2023 figures. You can see that the highway mileage went up by 2 mpg compared with the hybrid version; but compared with the “straight” Hemi V8, both city and highway numbers went up by 3 mpg for rear-drive trucks, and city went up by 2 mpg with highway up by 3 mpg on 4x4s. (The difference is likely due to rounding, since the EPA doesn’t report decimal places.)

Ram 1500 RWD 4x4
2023 Hemi 15/22 15/21
2023 V8 Hybrid 18/23 17/22
2025 I6-SO 18/25 17/24

In addition to writing about cars and Chrysler, David Zatz is an organizational researcher and change agent. He currently works with Toolpack Consulting and teaches classes in data analytics, decision making, and strategy for Fairleigh Dickinson University’s School of Public and Global Affairs.

Also see: Hurricane engine, 2025 Ram 1500, upcoming Ram 1500 Ramcharger

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