As a general rule, electric vehicles don’t have conventional multispeed transmissions as gas-powered cars do, with nearly all having just a single speed. (There are exceptions, which we’ll get to in a bit.) That’s largely because electric motors produce their full power as soon as they start to turn (meaning, from a dead stop) and continue producing it over a wide rev range.
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Peak power doesn’t sustain, but motors rev as high as 20,000 rpm in some vehicles. By contrast, gas engines typically top out (aka redline) around 6,000 or 7,000 rpm; have to be “revved up” to make their maximum power; and are most efficient, based on load, within a fairly narrow rev range. They require more than one speed to operate at low and high road speeds, especially with greater efficiency. A multispeed transmission that’s of value in a gas vehicle isn’t normally worth the considerable increase in weight, cost and complexity in an EV, but EVs still have a transmission of sorts.
Even EVs with just one speed still need gears that change the electric motor’s drive-gear ratio and transfer power to a differential, which splits that power between the wheels. Furthermore, they may have a device that locks the gears when Park is engaged. In most EVs, selecting Reverse simply makes the electric motor spin in the opposite direction, so separate gears for that aren’t needed.
Exceptions to the Rule
One of the first modern EVs was the Tesla Roadster, introduced for the 2008 model year as a small, two-seat sports car with a rear-mounted motor and rear-wheel drive. Very early versions used a two-speed transmission, but it was soon replaced by a single-speed unit.
Another exception is the current Porsche Taycan, a high-performance four-door offered with a rear motor and rear-wheel drive, or front and rear motors and all-wheel drive. Interestingly, it has a two-speed transmission only in the rear, with the front motor (on AWD models) driving the front wheels through a single-speed transmission. Porsche claims the two-speed transmission enables both strong off-the-line performance and better efficiency and range at the very high speeds traveled on the German Autobahn. In Porsche’s case, a two-speed transmission can be more easily justified in the Taycan because it’s a performance-focused EV with a top speed of more than 140 mph and a starting price north of $80,000, with high-end AWD models topping out around 160 mph and $185,000.
It’s possible that the common practice of using just a single-speed transmission in electric vehicles may change. Porsche’s example of using a two-speed transmission — if only in the rear — may be a harbinger of things to come, as many advancements in EV technology appear first in high-priced vehicles, later trickling down to lower-priced ones.
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