How Car Suspensions Work

Specialized Suspensions: Hot Rods

1923 T-bucket
1923 T-bucket
Photo courtesy Street Rod Central

­The classic American hot rod era lasted from 1945 to about 1965. Like Baja Bugs, classic hot rods required significant modification by their owners. Unlike Bu­gs, however, which are built on Volkswagen chassis, hot rods were built on a variety of old, often historical, car models: Cars manufactured before 1945 were considered ideal fodder for hot rod transformations because their bodies and frames were often in good shape, while their engines and transmissions needed to be replaced completely. For hot rod enthusiasts, this was exactly what they wanted, for it allowed them to install more reliable and powerful engines, such as the flathead Ford V8 or the Chevrolet V8.

One popular hot rod was known as the T-bucket because it was based on the Ford Model T. The stock Ford suspension on the front of the Model T consisted of a solid I-beam front axle (a dependent suspension), a U-shaped buggy spring (leaf spring) and a wishbone-shaped radius rod with a ball at the rear end that pivoted in a cup attached to the transmission. Ford's engineers built the Model T to ride high with a large amount of suspension movement, an ideal design for the rough, primitive roads of the 1930s. But after World War II, hot rodders began experimenting with larger Cadillac or Lincoln engines, which meant that the wishbone-shaped radius rod was no longer applicable. Instead, they removed the center ball and bolted the ends of the wishbone to the framerails. This "split wishbone" design lowered the front axle about 1 inch (2.5 cm) and improved vehicle handling.

Lowering the axle more than an inch required a brand-new design, which was supplied by a company known as Bell Auto. Throughout the 1940s and 1950s, Bell Auto offered dropped tube axles that lowered the car a full 5 inches (13 cm). Tube axles were built from smooth, steel tubing and balanced strength with superb aerodynamics. The steel surface also accepted chrome plating better than the forged I-beam axles, so hot rodders often preferred them for their aesthetic qualities, as well.

Some hot rod enthusiasts, however, argued that the tube axle's rigidity and inability to flex compromised how it handled the stresses of driving. To accommodate this, hot rodders introduced the four-bar suspension, using two mounting points on the axle and two on the frame. At each mounting point, aircraft-style rod ends provided plenty of movement at all angles. The result? The four-bar system improved how the suspension worked in all sorts of driving conditions.