Is it solely a case of one-upmanship that is driving the number of forward gear ratios forward in today's passenger cars? Or, are consumers choosing vehicles based on the number of gears in the transmission? I am not entirely sure, but I do know that I would consider passing on a vehicle just because it only has a four-speed transmission. As rare as they are today, some vehicles, like the GM full-size pickups, are still using four-speed automatic transmissions. Before you comment, I know that they are being phased out in favor of the new six-speeders. But, a little research shows that Mercedes and BMW offer seven speed automatics, and Lexus has an eight speed for their top-of-the-line model. Why so many gears? Efficiency is one reason, and performance is the other. We'll start with the latter.
Do you remember the old Power-Glide trannys that GM used when muscle cars were just hitting the scene? I'm not old enough to remember, but I have experienced them after-the-fact. They worked fine, but if you were cruising in second gear and hit the gas causing a downshift, it might be rather abrupt, because there was only one choice for the transmission to make. In the newer trannys with more gears, there are many choices. For instance, imagine cruising in gear eight, you hit the gas ... depending on how hard and at what speed you are traveling, you could drop to seventh for a gradual acceleration, or to fourth for fast pick-up. Conversely, only having two forward gears in the Power-Glide allows for excellent reliability and it also makes them predictable, which is why they are still popular transmissions for drag racing.

Now, as far as efficiency is concerned, if you are driving slowly, the transmission can up-shift to a lower numeric gear ratio, saving gas in the process. I have never driven a car with more than six forward gears ... so I can't say what the driving experience is like, but it is certainly a market trend to increase the number of forward gears. For maximum efficiency, a manufacturer may choose a CVT with an infinite number of ratios, but some consumers don't like the driving experience with them. So I would expect to see more and more new transmissions like this ZF with eight forward gears. The more the merrier?

[Source: Gizmag]

Share This Photo X