Not All Automatic Transmissions Are Created Equal
If you are in the market for a new or used car, you probably want one with an automatic transmission. Compared to a manual, automatic transmissions are easier to use and particularly convenient in stop-and-go traffic. If you have been out of the auto market for some time, you may not be aware that there are now several types of automatics in use, some with driving characteristics quite different than those to which you may be accustomed.
Conventional automatic transmissions, which shift smoothly, but are heavy, complex and expensive to purchase and repair, are still the most common type. In the past, this type of transmission reduced fuel economy, but modern computer-controlled conventional automatics often provide better gas mileage than a manual transmission in the same car. They can also be programmed to shift much more quickly than in the past.
Continuously Variable Transmissions (CVTs) offer up to a 10 percent increase in fuel economy by providing an infinitely variable range of gear ratios. When a car with a CVT accelerates, the engine rpm rises fairly high and remains there while the transmission gear ratio is varied to increase vehicle speed. Many drivers do not like this characteristic, so some CVTs are programmed with gear ratio “steps” that simulate the operation of a conventional automatic.
The newest type of automatic, the dual-clutch transmission (DCT), is essentially two manual gearboxes operating in parallel. A DCT has two shafts, one for the odd-numbered gears and one for the even-numbered gears, each controlled by its own clutch. A computer uses several inputs to preselect gears and apply one clutch or the other as necessary. DCTs can shift very quickly and, like a CVT, offer up to a 10 percent improvement in fuel economy. A DCT automatic transmission also contains fewer and potentially more durable parts provided proper car maintenance is performed. DCT downsides can include abrupt clutch engagement when leaving a stop, and short delays in shifting when the needed gear is different than the one preselected.
When shopping for your next vehicle, it’s important to understand what type of automatic transmission it has and how it will change your driving experience. Then, take a thorough test drive where you can operate the car at various speeds, travel uphill and downhill, and rapidly accelerate and decelerate. If the transmission behavior is to your liking, great. If not, try out vehicles with other transmission types to find the one you like best. What might seem like a minor glitch on a test drive can turn into a major annoyance as time passes and the miles add up.
Regardless of your final automatic transmission choice, a friendly word of caution is in order. To avoid a premature visit to your repair shop, always use the brakes to hold the vehicle in position when stopped on an uphill grade; never use the throttle. Using the accelerator can overheat the transmission fluid and will cause accelerated (and expensive to repair) clutch wear in some CVT and all DCT transmissions.
For more in-depth information on automatic transmissions, click here to read a comprehensive AAA Automotive Technical Update on this topic.