Rear suspension

For front-wheel drive cars, rear suspension has few constraints and a variety of beam axles and independent suspensions are used.

For rear-wheel drive cars, rear suspension has many constraints and the march to the superior but more expensive independent suspension layout has been a long slog. The dynamics of such a vehicle are that the rear suspension must counteract by the tendency of the rolling wheel traveling in the opposite direction from the vehicle. This must be countered by the rear suspension taking up a counter-clockwise torque; otherwise, the body and frame of the car will strip itself off the rear suspension, whatever it is. It is that need which dominates several of the varieties of rear suspension.

Henry Ford's Model T used a torque tube to restrain this force, for his differential was attached to the chassis by a lateral leaf spring and two narrow rods. The torque tube surrounded the true driveshaft and exerted the force to its ball joint at the extreme rear of the transmission, which was attached to the engine. A similar method was used by the late-1930s Buick and by Hudson's "bathtub car" of 1948, which used helical springs which could not take fore-and-aft thrust.

Hotchkiss drive is the name of the most popular rear suspension in American cars from the 1930s to the 1970s. It was invented by a Frenchman. His system uses longitudinal leaf springs attached both forward and behind the differential of the live axle. These springs transmit the torque to the frame. Europeans consider this primitive technology(Though Citroen, Aston Martin, Volvo, and many more had used live axles during this period in at least a few of their autos), not producing good ride quality or car handling, but it was accepted by American car makers because it was inexpensive to manufacture. Also, the dynamic defects of this design were suppressed by the enormous weight of US passenger vehicles before implementation the Corporate Average Fuel Economy standard.

Another Frenchman invented the De Dion tube, which is sometimes called "semi-independent". Like a true independent rear suspension, this employs two universal joints or their equivalent from the center of the differential to each wheel. But the wheels cannot entirely rise and fall independently of each other; they are tied by a yoke that goes around the differential, below and behind it. This method has had little use in the United States, though it does not evidence the bump steer that a more expensive, true independent suspension does. Its use around 1900 was probably due to the poor quality of {tires|tyres}, which wore out quickly. By removing a good deal of unsprung weight, as independent rear suspensions do, it made them last longer.

Rear wheel drive vehicles today frequently use a fairly complex fully independent, multi-link suspension to locate the rear wheels securely while providing decent ride quality.