If an automobile engine is described as transverse mount, it means that the crankshaft lies perpendicular to the direction of the vehicle's movement. This is also known as an east-west mount engine. The alternative is called a longitudinal-mount engine.
If an engine is mounted transversely in a vehicle, it is almost always either front wheel drive or four wheel drive, or uses a chain/belt to drive the rear wheel(s), as is the case with many motorcycles.
The first ever transverse mount front drive car was the Mini in 1959, which used an under-engine, in-sump gearbox, sharing an oil source with the engine.
The primary advantages of transverse mount engines include:
- Engine can be mounted closer to the centre of the vehicle without intruding into the passenger compartment, allowing for better front/rear weight distribution.
- Engine can be mounted in a slant alignment without causing problems with left/right weight distribution.
- Vehicle can have a shorter nose, or shorter tail in the case of rear/mid engine cars.
- Engine spins in the same axis as the wheels, meaning (in the case of front drive cars or rear engine rear drive cars) there is no need for heavy driveshafts running under the length of the car, nor does the differential gear have to be separate from the gearbox.
- In the case of motorcycles, and some go-karts, no differential gear is necessarily at all.
Disadvantages of transverse mount engines include:
- Rotational inertia of the engine can upset front/rear stability of a vehicle under rare circumstances.
- Driveshafts are usually of uneven lengths, which can lead to torque steer in some cars.
- CV joints have to be used in cars where the front wheels are driven and are high-wear items.
- Gearbox usually has to be mounted to one side of the engine, which can upset left/right weight balance, and usually also means that the engine must be at least partially removed for clutch/gearbox replacement.