Dear Tom and Ray: Years ago, it was understood that manual-transmission cars had better fuel economy than the same cars with automatics. But for the past several years, as manual transmissions become increasingly scarce, the dealers (and EPA) claim that the mileage is the same due to improved automatics. I don’t believe this. What’s your opinion, and do you think they just quit testing the manual cars, and slap on the same rating? I’m looking to buy a new car, maybe manual. – Barbara
Tom: It’s true, Barbara. You’re right to be a bit skeptical of the EPA’s mileage numbers. The EPA doesn’t actually test any cars; the manufacturers do the testing and then report their numbers to the EPA.
Ray: We know of at least one case of admitted fudging, by Hyundai. And another case in which Ford admitted to some “calculation errors,” and had to revise downward the mileage numbers for a bunch of its hybrids.
Tom: So the EPA numbers are really just estimates. In our real-world testing, the mileage numbers we get often are lower – particularly in city and mixed driving. For some reason, the highway numbers often come pretty close.
Ray: But, in general, we do believe that modern automatic transmissions do as well as or better than manual transmissions, as far as mileage.
Tom: There are two reasons for that. One is the number of gears. It’s not uncommon now for automatic transmissions to have between six and nine forward speeds. And with the international “gears race” in full swing, I’m sure 10- and 11-speed automatics are just over the horizon.
Ray: There also are continuously variable automatic transmissions (CVTs). They use pulleys to constantly adjust the gear ratio, giving them, theoretically, an infinite number of gears.
Tom: The more gear ratios you have available, the easier it is to find the most efficient one at any given moment. And that improves the car’s overall mileage.
Ray: The second factor is the lock-up torque converter. The reason manual transmissions used to get better mileage is because there’s no “slop” in them. You put the car in the gear, take your foot off the clutch, and the car is “locked” in that gear until you remove it.
Tom: That’s why a car with a manual transmission will stall if you come to a stop without taking it out of gear.
Ray: Automatics use a viscous, fluid coupling, which allows the transmission to “slip” when you’re stopped at a light, to prevent the engine from stalling.
Tom: But that same fluid coupling that allows the transmission to slip at low speeds was harming mileage at higher speeds.
Ray: The lock-up torque converter solved that problem by, essentially, allowing an automatic transmission to “lock” into gear (automatically) at higher speeds, like a manual transmission would – and then unlock when you slow down and need a traditional automatic transmission again.
Tom: So automatics do get comparable, if not higher, mileage these days.