Mid or Rear Engine: what’s the diff?

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There's more than one way to have an engine in the back, like a mid-engined Ferrari or a rear-engined Porsche. Image from Wikimedia Commons.

There’s more than one way to have an engine in the back, like a mid-engined Ferrari or a rear-engined Porsche. Image from Wikimedia Commons.

Though very few cars utilize the layout, a number of people use the term “rear engine” as a catch-all for any car that doesn’t have a motor in the front. The truth is that very few cars actually ARE rear-engined, which has to do with some rather esoteric, though logical, reasons.

Very few actual rear engine cars

Believe it or not, the rear-engine layout is very rarely used. Only one rear-engine car is on the market today in any sort of capacity.

Oh, but what about Ferraris or Lamborghinis? The engines are in the back, some might say. Those cars aren’t rear-engined, but are actually mid-engined. What’s the difference, you might ask? Well, it has to do with the nomenclature behind drivetrain layouts.

Don’t be an axle

The difference between rear-engine and mid-engine layouts has to do with where the engine is located relative to the closest axle. A true rear-engine layout has the motor positioned directly over or behind the rear axle.

Likewise, a mid-engined car, such as the aforementioned Italian exotics has the engine positioned ahead of the rear axle. However, another wrinkle is such a thing exists as front mid-engined, so the favored rides of oil sheiks and superstars are – to put it more accurately – rear mid-engined.

A front engine car, likewise, has the motor positioned above or in front of the front axle, and front mid-engined cars have the motor positioned behind it.

Thus, true rear-engined cars are quite rare. The only one available on any large scale is the Porsche 911. All of Porsche’s other cars are mid- or front-engine.

Difference between mid and rear

There are some functional differences between a rear mid-engine car and a rear-engine car. Rear-engine cars, with so much weight hanging off the back, tend to have inertial characteristics which tend toward oversteer during cornering.

Imagine the swing of a pendulum. Now, as a, say, Porsche 911 enters a corner at speed, the pendulum swings to the outside of its arc due to inertia. Given sufficient inertial energy to break the grip (frictional adherence to the road surface), the rear end slides in the opposite direction of the turn, or “oversteers.”

Rear mid-engine cars have much more balanced weight distributions (most of the weight is in the middle) and handling characteristics, hence it’s popularity in serious performance cars. Granted, they’ll still oversteer with the best of them.

Rear and rear mid-engined cars also have to employ different drivetrain layouts. A front-engine, rear-wheel drive car (most performance vehicles) employs an upside-down “T” configuration; the engine connects to the transmission, which sends a prop shaft to the differential at the back, driving the wheels. A rear-engine or mid-rear engine car often has requires the engine be mounted transversely (side-to-side) and the transmission and rear diff have to be incorporated into a single system, called a “transaxle,” to fit in the allotted space.

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