Car geekery part 3: automatic transmissions with clutches

As much as I like cars, there aren't too many technical innovations in them that I'd be willing to pay for. An exception is what I'll call an automated manual transmission. Once a rarity (think Ferrari F1 cars and BMW M3s), they have slowly approached my price range (Audi/VW DSG, still not there). But lo and behold: this year we get a dual clutch automatic transmission in the 2011 Ford Fiesta ... for about $14k. This is a car I'd actually consider buying.

What is an automated manual transmission? You can think of it as a stick-shifter with the addition of a computer that can shift for you. How is this different from a conventional automatic transmision? In a car with a stick, there's a solid mechanical connection (through a clutch plate) between the engine and the wheels. In contrast, a conventional automatic puts the engine's power through a fluid connection (the torque converter). They're called "slushboxes". Think of sticking a spoon in a jar of honey and twisting the spoon to spin the jar. The drawbacks are delays, inefficiency, and less sense of being connected to the road.

Inefficiency, yes. Fuel economy is everything these days. Everybody knows manuals get better gas mileage than automatics--they're lighter, they don't waste power churning fluids, and they have more gears to choose from. Nonetheless I was startled to see the EPA estimates for the Fiesta:
Manual: 29 city/38 highway
Automatic: 30 city/40 highway
Um, what? The automatic gets BETTER mileage than the manual? Yes - it's doubtless heavier but it has one more gear.

On the downside, apparently you cannot choose what gear to be in, so you can't downshift in preparation for a passing maneuver. I think I'm OK with that. What I really want is the immediate response. I hate pushing the accelerator and waiting for my car's automatic to raise the engine revs and tighten the torque converter before I start to accelerate.

Jalopnik thinks very highly of this car, despite it only having 120 horsepower. It's light and has a great suspension, which is actually a lot more important to me than the powertrain. I know from experience that having more power just makes me drive like a jerk. What I enjoy is being able to go around corners without slowing down. This could be my next car.

Previous car geekery: part 1 and part 2.


  1. Modern automatics have lockup torque converters. When the converter's slip action is not needed a mechanism latches the two halves together solidly, eliminating that source of inefficiency. It's another set of parts and additional weight but it does make automatics more efficient at fixed speeds. There used to be a big difference in fuel economy between manuals and automatics when the choices were a 5 speed manual or a Turbo-Hydro-Matic slushbox. As this gap has closed manuals have gone from being the preference of fuel conscious drivers to being produced primarily for an enthusiast audience.

  2. My old Guzzi motorcycle has the strangest transmission on earth (other than a DAF with CVT through a leather drive belt). The Guzzi has a 2-range manually shifted gearbox and a torque converter. Basically unless you're climbing a hill, you leave it in one gear all the time, making it a 1-speed transmission. The torque converter means you don't have to declutch and shift in stop/go driving. It's dreadfully wasteful on gas but a ball around town.

  3. I still see differences in fuel economy in favor of manuals in most cars--maybe 5%, but it's always there. Probably churning losses from the RPM differences between the locked torque converter and the housing.

    My understanding is that almost all motorcycles have sequential manuals, like those first BMW M3 SMGs. I saw one on recently for $17k. Hard to believe, but that design was a failure for BMW.

  4. In other news, you can now get the VW DSG in a Polo GTI. But it's still $28k. I think this Ford is going to be a tremendous little car. I can't wait for the transmission filter up into the rest of their lineup.

  5. Any automatic will always have a weight penalty in addition to more frictional losses than a comparable manual. Sequential manuals are used in some race cars because they're light, rugged and shift quickly. I can see why they failed in road cars, though.
    Automobile transmissions are due for a revolution. Engines have changed a lot in 30 years but transmission advancement has been limited to the upper end brands.
    Exception: Subaru had a CVT in the Justy 23 years ago. Those are becoming more common now that modern designs can handle more torque.