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After your gas engine and accessories have wasted energy, they pass on about 19-25% of it to the transmission/gearbox (drivetrain). Gasoline and Diesel engines need a transmission because they only make good power in a narrow range of engine speeds (RPM), while cars need to go a wide variety of speeds, from parking lots to freeways.

By giving the motor different gears to send the power through, the car can do all that it does, but at a cost. As the power goes through the gears, clutches and other parts, some of it is lost to friction and heat.

Most hybrids have a transmission, but it accepts power from both a gas/diesel motor and one or more electric motors. These types of hybrids still suffer from the same drivetrain losses as gas cars, but without the idling and standby losses.

EVs and “range extender” hybrids, plus some “plugin hybrids”, have an electric motor that has a simplified gearbox or no gearbox at all. These types of vehicles suffer little to no drivetrain losses.

Types of Transmissions/Gearboxes

Not all transmissions/gearboxes are created equal. Some waste far more energy than others, but there are ways to improve the situation. While the automotive world has seen many types of different transmissions over the decades, I’ll cover the four most common types:

  • Manual (aka “standard” or “stick”)
  • Automatic Transmissions
  • CVT or “Cone Clutch”
  • Dual Clutch (aka “DCT” or “DSG”)

Volumes can and have been written about these transmissions, so I will not be able to cover each type in depth. What I will be doing is talking about the gas mileage pros and cons to each type and discuss how to get the most out of each.

Manual Transmissions

The manual transmission is one of the best transmissions you can get for fuel economy. Its great strength is simplicity.

Pros

  • Simple design minimizes power wasted
  • No slippage when in gear, more direct power to wheels
  • Driver gets more control over the car, enabling better performance and efficiency with a skilled user
  • No unwanted “kickdowns” – it won’t downshift when you didn’t want it to

Cons

  • Requires more skill to drive, but it’s not as hard to learn as many seem to think
  • Requires more attention, which could be a problem for some drivers (mental disabilities) and professions (police, fire, EMS)
  • Power is lost during shifts, shifts can be slow depending on driver

How To Get The Most Out Of This Transmission

I can’t teach you how to drive a stick here, but assuming you know the basics, here are some things you can do to increase your mileage:

  • Shift earlier. Keep RPMs low, but not too low (where it shudders).
  • Don’t spend too much time on your clutch.
  • Don’t downshift when climbing hills unless the engine RPM would go too low or you lose too much speed (avoid “lugging”/vibration).
  • If your car has deceleration fuel cutoff, don’t coast in neutral when coming up to a stop. Stay in a higher gear to keep the fuel cut off for as long as safely possible while not braking much.
  • Be sure to “engine brake” with lower gears when going down hills so fuel will be cut off instead of idling and burning gas.

Automatic Transmissions

The most common type of transmission in the United States, but not in many other countries. Automatic transmissions use a torque converter instead of a clutch to allow slipping. This prevents stalling at low vehicle speeds and allows shifting from gear to gear.

Pros

  • Doesn’t require much skill to drive.
  • Easier for the disabled.
  • Less power loss during shifts

Cons

  • Torque converter slips and wastes energy (and fuel) unless torque converter clutch (TCC) is locked. Some cars lock up at lower speeds than others, with some only locking on the highway. Older automatics (before the 1980s-90s) didn’t lock up at all.
  • False sense of security, encourages inattention in some drivers.
  • Many automatics shift late, downshift too easily, and keep engine RPMs up too high for best fuel economy, while also shifting wrong in many performance driving situations.

How To Get The Most Out Of This Transmission

  • Find out when your TCC locks, and try to keep it locked if possible:
    • TCC may lock above a certain speed
    • TCC might engage more in “sport” or “eco” mode if your car has this
    • TCC might lock more in “manual”, “tiptronic”, “manumatic”, or “+/-” modes.
  • If you are driving at a speed too low for your car’s TCC to lock, move your gas pedal up and down slightly. You’ll see the tachometer needle wiggle up and down a number of RPMs. Don’t let the car sit at the top of this wiggle room all the time. Slightly releasing the throttle and going to mid-range of the wiggle room can help save gas without decelerating as much as you would taking your foot completely off the throttle.
  • If your engine RPMs climb above 2500 during light acceleration, briefly release the gas to trick the transmission into upshifting.
  • Use the shifter to force the transmission into a lower gear for light engine braking when coasting up to a stop. This helps keep deceleration fuel cutoff going for longer.
  • Use lower gears when going down steep hills. This keeps speed under control without brakes, and keeps deceleration fuel cutoff going.

Use manual mode if you have it.

If your car has a manual mode, aka “tiptronic”, “manumatic”, or “+/-“, USE IT!

By taking more control, you can get better fuel mileage using the tips in the above section. You can also look at your MPG/economy readings and learn how to get your car to sustain higher MPG (more on this in upcoming lessons).

CVT Transmissions

Continuously Variable Transmissions (CVT) don’t have gears like most transmissions. Instead, they have a “cone clutch” or similar mechanisms that allow for a range of infinitely variable gear ratios instead of a number of fixed gears. Engines optimized for these transmissions can be much more efficient, and for this reasons CVTs are very common in hybrids, often as a part of the overall transmission.

 

Pros

  • Engine can be kept at its most fuel efficient or most powerful RPM while shifting gear ratio to adjust speed of vehicle to match
  • Less wasteful than an automatic transmission
  • Fewer moving parts; less expensive to make

Cons

  • Not available in heavy or powerful cars due to design limitations
  • Unfamiliar feel for many drivers at first
  • May require more maintenance (belt changes)
  • Still requires a clutch or torque converter to prevent stalling when stopping

How To Get The Most Out Of This Transmission

Keep acceleration moderate, but don’t worry about keeping RPM low as much. The CVT will select the best ratio, and keeping the RPM in the right range will do more to help efficiency than trying to keep the RPM low.

Some drivers have said these transmissions are good at coasting. Either way, keep an eye on your fuel efficiency gauge (MPG) and adjust your driving for the best mileage.

Dual Clutch Transmissions

Designed to be the “best of both worlds”. They shift like an automatic, but have manual transmission guts. Computers control the shifting, allowing for lightning-fast shifts with nearly immeasurable power output loss during the shift. Superior to most automatic and manual transmissions for fuel economy.

Pros

  • Fast, precise shifts that are humanly impossible in a manual
  • Low power loss during shifts
  • Very little slipping during shifts, no slipping when in gear
  • Almost always comes with a “manual mode” or “sport mode”

Cons

  • Some manufacturers are still figuring out how to build them right.
  • More expensive than most transmissions
  • May feel weird to some drivers, especially when taking off from a stop

How To Get The Most Out Of This Transmission

  • Use the “manual mode”
  • Shift earlier. Keep RPMs low, but not too low (where it shudders).
  • Don’t downshift when climbing hills unless the engine RPM would go too low or you lose too much speed (avoid “lugging”/vibration).
  • Coast in the highest gear you can to minimize energy loss until you begin to approach a stop.
  • Don’t coast in neutral when coming up to a stop. Downshift and use light engine braking. Stay in gear to keep the fuel cut off for as long as safely possible.
  • Be sure to “engine brake” with lower gears when going down hills so fuel will be cut off instead of idling and burning gas.

All Wheel Drive (AWD) and Four Wheel Drive (4WD)

All wheel drive and four wheel drive are great for a variety of tough conditions your vehicle may encounter. They can be great for versatility and safety, but they increase driveline losses between the transmission and the wheel.

Four wheel drive systems should never be used on dry pavement. If your vehicle has four wheel drive, leave it turned off on the roads. Also, minimize use of low range (4 Low, 2 Low) to when you really need it.

If conditions are good and you are on dry pavement, you might be able to turn an all wheel drive system off. Many cars have a button or switch for this. Just hit the button and turn the system off to restrict power to two wheels. If there’s no button, keep in mind that many all wheel drive systems turn off above a certain speed to save gas all on their own.

If you aren’t sure about your all wheel drive car, look at your owner’s manual for more detailed information on your all wheel drive system.

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