Corvette Frames - Good Foundations

When It Comes To Corvettes, It's Often What's Underneath That Counts

From the April, 2011 issue of Vette

By Walt Thurn

Photography by Walt Thurn

The C6 Corvette is known for its lightness, strength, and superb handling. These traits are linked directly to the car's structure, which has evolved dramatically since the marque launched nearly 60 years ago. In the pages that follow, we'll take a look at how Corvette frames have evolved from 1953 to today.

The first Corvettes had two major structural components-a large, boxed steel frame and a hand-built fiberglass body. The production team installed the engine, suspension, brakes, driveshaft, and rear differential onto the steel frame. The completed body was then bolted onto the finished frame and readied for shipment. This assembly method remained unchanged until C1 production ended in 1962.

The '63 C2 Sting Ray was an all-new design that included independent rear suspension and a coupe body. The design engineers still used a separate steel ladder frame bolted onto a fiberglass body, but the body construction changed. A new steel cage was engineered, and the fiberglass panels were attached with a bonding agent. When completed, the body was bolted to a steel ladder frame with its running gear already installed. This resulted in a strong but heavy Corvette. This method remained through 1982, when C3 production ended.

The fourth-generation model brought a major change in how Corvettes were built. A new steel frame was welded together to form a single unit, and the body panels were glued to this frame. The engine, transmission, suspension, driveshaft, and differential were attached to two separate steel cradles, and a long, aluminum torque bar connected the front and rear frame sections. When the body and driveline sections were completed, they were joined together on the assembly line. This resulted in a Corvette that was lighter and stronger than in previous generations. This assembly process continued until the end of the C4 production in 1996.

When engineers began developing the fifth-generation Corvette, they studied the fourth generation to determine what needed improvement. They discovered that the car's steel structure would flex under spirited driving conditions. The C4's two side framerails consisted of three pieces that were welded together to form one beam; engineers discovered that these welds were the source of the flexing.

The C5 design team found a clever solution to this problem: It made the new frame out of a 14-foot-long, 3mm-thick steel tube. The tube was closed off at each end and filled with high-pressure water. The water bent the steel into the correct shape without welding. This new process was named hydroforming and was introduced in 1997. Frame strength proved so high that when the convertible was introduced in 1998, it didn't require any extra bracing.

The sixth-generation Corvette, introduced in 2005, featured a completely new body wrapped around a fifth-generation frame. Not long after the car's debut, Chief Engineer Dave Hill and his team began working on a new Z06 model. They wanted the new version to be lighter and faster than its C5 predecessor, so they decided to reduce the car's weight with lightweight materials. These included aluminum, carbon fiber, and titanium.

A new hydroformed frame was constructed from annealed, 4mm-thick 5745 aluminum alloy. The standard C5/C6 steel frame is 3 mm thick and weighs 502 pounds, while the Z06 frame is 4 mm thick and tips the scales at 392 pounds (22.5 percent lighter). Even better, the Z06 frame is 50 percent stronger in bending resistance and torsional stiffness. Continuing the theme of ongoing improvement, it's also the first car to use laser welding and self-piercing rivets in a mass-production environment. The final result is that the Z06 Corvette tips the scales at just 3,130 pounds.

Because of the car's low production volume, the aluminum frames are built at the Metalsa (formerly Dana Manufacturing) plant in Hopkinsville, Kentucky. The completed frames are then shipped to Bowling Green for final assembly. In 2009 the higher-performance ZR1 was added to the Corvette lineup; it uses the same Z06 aluminum frame built at the Metalsa plant. As you can see, when it comes to modern Corvettes, every model is built on good foundations.