GM to merge Zeta and Sigma chassis

One of the oddities of GM's platform strategy is that they have two large rear-drive architectures that are similar in size. Sigma and Zeta. Sigma is Cadillac's dedicated rear-drive chassis that debuted in 2003 on the original CTS and has seen duty under the SRX, STS, and the new 2nd generation CTS. It's two downsides are that it is relatively expensive and can't be shared with other, higher volume models (some would call this a benefit) and that the chassis can't be expanded much beyond the size of the current STS. Zeta is GM's latest rear-drive architecture that was developed primarily by GM's Holden division and is aimed at the lower costs needed by volume brands such as Holden, Pontiac, Chevrolet, etc. According to, GM has decided to merge the development of these two chassis. By planning the merged architecture for both luxury and volume models, they will be able to cut costs of all models without giving up the premium features that Cadillac customers expect. MT is expecting 6 different versions of the new chassis: Coupe - short version that will see duty in volume models like the Holden Monaro, Chevy Camaro, and possibly a Pontiac G8 coupe Coupe Premium - Next generation CTS coupe, differs from the standard coupe version with premium construction and suspension tuning Midsize - Holden Commodore, Pontiac G8, Chevy sedan Midsize Premium - Next generation CTS, same premium suspension as the premium coupe Large - Holden Statesman, Buick Park Avenue in China, Holden Ute, Pontiac G8 Sport Truck, Large Buick sedan Large Premium - STS/DTS replacement again with upscale upgrades and suspension changes Additionally, GM is still expected to be working on the Alpha chassis in standard and premium versions for the Cadillac 3-Series competitor and also smaller rear-drive models for Holden, Pontiac, and Chevy. Read all about it at: GM's latest rear wheel drive vehicle plans