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2012 Subaru Impreza (Subaru)
2012 Subaru Impreza (Subaru)

Rob's Garage

Don't rule out a CVT until you try one Add to ...

Hi Rob

Subaru is coming out with a new Impreza in 2012. Unfortunately (in my opinion), it is equipped with a CVT transmission. People tell me CVTs do not accelerate when you needed it most as in passing situations. What do you think?

Thanks very much, Ray

Like you Ray, I used to believe that continuously variable transmissions (CVT) were not the way to go. As a serious car guy, I had to feel the kick of a transmission shift to keep a sense as to what was going on under my hood.

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Ray, this is all changed now. Technology continues to march along whether we like it or not and in the case of CVTs, it's all good. We are seeing a proliferation of these devices for a many reasons - not the least of which is fuel economy. Consider a bicycle: the more gears you have at your disposal, the more efficient the bike and the easier it is on the rider.

Now consider that a CVT has an almost infinite number of gears. For the uninitiated, a CVT operates using two variable diameter pulleys or cones as its key components. I'm over-simplifying, but one pulley is connected to the engine while the other pulley is connected to the driving wheels. Between the two is a chain link belt.

Through the use of electronics and hydraulics, the engine pulley or drive pulley diameter can be made larger or smaller and the wheel connected or driven pulley can be made smaller or larger in diameter. By making the drive pulley larger in diameter and the driven pulley smaller in diameter, high speed is achieved but at the cost of a reduction in torque - overdrive. Reverse this scenario and you'll have low speed but high torque - just as you would find on the gear set on a 21-speed mountain bike. Now imagine that these two pulleys can change diameters independent of each other and in (almost) an infinite number of combinations; you can see that this transmission can deliver an amazing number of gear combinations.

Now here's the kicker - perception. This was what I used to have a problem with also. Because a CVT has the ability to affect vehicle speed and drive torque (not to be confused with engine torque) independent of the speed of the engine, pulling away from a light sounds and feels different.

Typically when you press the throttle, the car's engine builds revolutions per minute (RPM) finding its peak torque output, and stays at that level. What you hear is a constant engine purr that gives you the perception that the engine is not contributing to the acceleration of the car...when in fact, the opposite is true. This is where the efficiencies of the CVT comes in. The engine reaches peak torque, which coincides with near maximum volumetric efficiency, i.e. fuel economy. The engine can remain at this RPM for an extended period of time while the CVT makes adjustments to the drive wheels. This is what will feel strange to you, because the car accelerates, but the engine doesn't increase in RPM.

Like you Ray, I had a tough time absorbing this phenomenon. And apparently we were not alone in this perception because the manufacturers have had to program the electronics to make the CVT feel like shifts take place...even though they don't have to.

So Ray, don't dismiss the new Subie for the sake of its CVT. Take it for a drive when it gets here, and also test drive a Nissan Murano. Like the Subie, it uses a CVT.

Send your questions for Rob MacGregor to globedrive@globeandmail.com

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