Here’s the latest reader question, along with my reply!
Chaz asks: My dad has given up on Subaru because of their insistence on using CVT transmissions. Since you are my car “sensei” I was wondering how you felt about these relatively new transmissions.
My reply: CVTs – continuously variable transmissions – have been in general use for about 20 years now; I know, time flies! They offer an efficiency advantage (manifested as gas mileage) over conventional automatics, which have a fixed number of forward gears (e.g., a six-speed automatic).
The CVT – often described as having just one forward “gear” (e.g., Drive) actually has a continuously – and infinitely – variable number of possible ratios, changing incrementally as required by load on the engine, road speed and so on.
In a fixed-gear automatic (or manual) each gear is optimum for a given load/road speed, but as the car goes faster – or slows down – or the load increase (or decreases) the transmission has to jump up (or down) from one gear to the next, missing out on the more optimum “in between” ratios. Also there is the time it takes to shift up or down, and friction losses as gears are engaged – and disengaged.
The CVT does its thing by always maintaining the ideal drive ratio for any condition, without ever having to shift up or down.
Subaru – which has a deserved reputation for unusually thirsty engines given the relatively small size of its engines – needed to improve its MPG numbers, if only for the sake of complying with federal fuel economy mandatory minimums (CAFE). The CVT was a big part of the plan and if you have a look at current Subaru city/highway mileage numbers, you will see they’ve gone up significantly.
Other car brands use CVTs for the same reason.
They’re not bad transmissions – in the sense of being unusually expensive or prone to problems (generally; the early models had some teething issues). But their operating characteristics can be off-putting, especially in a car with an engine that doesn’t make a lot of power.
The tendency is for the CVT to let the engine rev fairly high – close to redline, if you have the pedal to the floor – and then hold the engine at fairly high revs (where it makes whatever power it does make) without the usual decrease in engine RPM (and engine noise) you’d experience with a conventional automatic or manual transmission as it shifts up through its forward gears.
Even in cars that have powerful engines, the car accelerates differently – almost like a jet on take-off roll, with continuous, linear thrust. This is actually a boon because there is no “shift shock” – the coffee-spilling forward/back lurch that occurs in a car with a conventional geared transmission during each upshift, especially at WOT.
But many people prefer the feel of the conventional, geared transmission. Which is why – ironically – many of the latest CVTs are set up to mimic shifts and are even advertised as offering this feature.
But there’s no “shift shock,” even so. Because no changing of gears – just varying of the ratio. A given ratio is simply programmed to be held – and then released – per the programming (or via the manual + and – paddle shift controls these cars often have).
So, it’s ultimately a question of what you prefer.
The CVT gives you mileage as good or even better than a well-shifted manual transmission with the convenience of an automatic. But you may not like the way the CVT behaves vs. the more traditional geared automatic or manual transmission.
Thus, as always, a test drive is in order!
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Got a question about cars – or anything else? Click on the “ask Eric” link and send ’em in!
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