Renault's PF3 platform vehicles have them. So does Cadillac's XLR roadster. And Mitsubishi's Japan-assembled Colt is fitted with supplier-assembled corner modules too.

Broadly speaking, brake corner modules contain the wheel hub and bearings, steering knuckle, brake rotor, disc, pads and calliper. Suspension or vertical corner modules also include the shock absorber strut and coil spring.

There are takers for corner modules among major car makers in Europe, North America and Japan. 'Younger' auto assemblers like Hyundai and Kia, with much less installed capacity, have also shown interest in the concept.

Suppliers have also found business among lower volume assemblers and for niche models.

But the market for brake and suspension corner modules has yet to really develop.

Penetration in North America is below 20%, and estimated to be well below that in Europe.

Supplier companies have been challenged to better their customers' assembly techniques and some of the potential benefits have yet to be delivered.

"In some cases we can do as good and sometimes better [than the OEM], through the value we can bring," says Bill Gillespie, Delphi's director of chassis engineering systems in North America. But "with large vehicle manufacturers our economies of scale might not be as good."

One of the big corner module suppliers is Auto Chassis International (ACI).

ACI supplies the corner modules to several Renault vehicles, and turns out around 13,000 module assemblies per day - roughly 730,000 vehicles annually out of the estimated 1.7 million vehicles were fitted with corner modules in Western Europe in 2003.

ACI was formed in 1999 as a fully-owned Renault subsidiary and operates primarily out of the former Renault Le Mans chassis engineering plant. ACI also supplies brake parts to the Nissan Micra in Europe, but the Japanese carmaker carries out all its own assembly.

Another potential benefit is management of tier 2 suppliers - Italian brake specialist Brembo recently won a contract in Europe where it replaced 32 different component supplies.

But it was a simple lack of space in Mitsubishi's Okazaki plant that drove the decision to buy an Akebono-managed corner module. Mitsubishi still direct-sourced most of the tier 2 suppliers for the module.

Akebono says a single point of responsibility for the module should result in shorter development times. Other market leaders in the sector are also focusing on improved integration of components.

Component integration is relevant to ease of assembly, for example by integrating the calliper and piston to the steering knuckle. Progress can also be made through tuning the sub-components to each other within the module, allowing better performance of the module overall, especially when wheels and tyres are mounted to the corner.

New cars continue to be designed with corner modules. But the difficulties of carrying out assembly more efficiently than their customers mean that other benefits have to show through for growth to increase.

Suppliers need to show that they can deliver cost effective solutions in the design and tuning areas before corner module growth accelerates.