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Rear-engine design


In automobile design, a rear-engine design layout places both the engine and drive wheels at the rear of the vehicle. The center of gravity of the engine itself is actually past the rear axle. This is not to be confused with the center of gravity of the whole vehicle, as an imbalance of such proportions would make it impossible to keep the front wheels on the ground.

Rear engined cars are almost always rear wheel drive, a layout known as RR. The exception is certain high performance four wheel drive models from Porsche.

This layout is typically chosen for three reasons, packaging, traction, and ease of manufacture:

  • Since the engine is located at an extremity, the rest of the vehicle can be used for passengers and luggage
  • Having the engine located over the driven wheels increase downward pressure which is helpful for grip on loose surfaces
  • The drivetrain can be assembled as a unit and installed easily at the factory -easier than a FF layout where the driven wheels also steer the car

The disadvantage of the rear engine configuration is that placing the engine outside the wheelbase creates significant problems for car handling as, when the car begins to slide on a corner, the end of the car will tend to want to swing wide and overtake the front — especially under braking. This tendency is referred to as oversteer and creates potential safety issues both for ordinary drivers, and even in racing applications. There are also occaisions where expert drivers find such behavior desirable in drifting, a motorsport based on intentional oversteer. Details on the handling characteristics of rear engined cars were prominently featured in the 1965 book Unsafe at Any Speed.

In addition, even though the rear wheels benefit from the additional traction the added weight of the engine gives, the front wheels still need traction in order to steer the car effectively. For this reason, a rear engined car can also be prone to understeer.

Most manufacturers have abandoned the rear engined layout apart from Porsche who has gradually developed their design with improvements to the suspension as well as electronic aids to reduce the shortcomings of the layout to acceptable levels.

On the De Lorean, to compensate for the uneven (35/65) weight distribution caused by the rear-mounted engine, the car had rear wheels with a diameter slightly greater than the front wheels.


The most well known rear engined cars


Automobile layouts
Layouts:
FF | FMR | FR | MF | RMR | RR | F4
Engine positioning:
Front-engine | Mid-engine | Rear-engine
Drive:
Front-wheel drive | Rear-wheel drive | Four-wheel drive | Six-wheel drive