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Why focus on city mileage?

by David Zatz on

Until recently, automakers seemed to work harder on boosting  highway mileage than city mileage, using aero tricks and gearing. Now, they are spending big money on weight loss and hybrids to gain city mileage. Why?

Aero and gearing work wonders on the highway, but city mileage is far more important to most people in actually using less fuel. While most consumers are attracted by highway economy numbers, e.g. “Up to 41 mpg!,” that doesn’t help much in meeting fuel economy rules.

annual gas savings in gallons

Start mpg
Gal. saved/
1000 mi.
10 9.1
15 4.2
20 2.4
25 1.5
30 1.1
35 0.8
40 0.6

Corporate average fuel economy (CAFE) requirements, which recently began to climb, are based on combined city-highway mileage. The quoted 50-mpg number is a bit of a game, given the huge number of loopholes in the law and outdated, optimistic test methods; but getting to a real combined 30 mpg (which is roughly what “50 mpg” translates to) will still take a good deal of work.

As an example, let’s say you have 35 mpg on the highway; going to 36 mpg sounds good but, for the average driver, that’s around ten gallons of fuel saved per year (which does adds up across a nation). Suppose you add that same 1 mpg to the city rating of, say, 20 mpg;  — now we’re talking 29 gallons per year, or three times as much.

This is the reason why every automaker is coming out with hybrid cars, stop-start systems, lightweight materials, turbochargers, and other tricks to help economy. The irony is that investment in these same technologies are likely to boost performance; just as automakers turned to advanced fuel injection, computerization, computer models, and metallurgy years ago to boost mileage and ended up with Spirit R/Ts (and finally Hellcats), these technologies can cut both ways. Cutting weight increases acceleration, all else being equal; advances in turbochargers and superchargers lead to quicker power boosts; and hybrids and electric cars may well be the next step in instant-on performance. It does all come at a price, but that price will likely come down in time, just as multi-port fuel injection is no longer an exotic, expensive add-on.


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