Dual Frame

Two years after the presentation of the famous orbital wheel, the hubless wheel, Franco Sbarro unveils the Helios program and the Dual Frame chassis concept.

Franco Sbarro and the Dual Frame chassis for the Helios program (photography Dingo)

The Dual Frame principle

The idea is to separate "structural dynamic functions from structural protection and comfort functions". In practice, this means dividing a car into two distinct parts:

A mechanical part (module 1, known as active safety) comprising the mechanics and the rolling structure. An engine-gearbox assembly, attached to a central-beam chassis, which includes all suspension components, guaranteeing rigidity and precision;

a trim section (passive safety module 2) corresponding to the bodywork, made of composite materials, and the passenger compartment. Between the two modules are pneumatic spheres, comparable to double-acting cylinders. These spheres inflate and deflate according to road conditions or driving style. Thanks to this pneumatic system, the ride height can be varied to eliminate pitching under acceleration, diving under braking and rolling when cornering.

Dual Frame modules linked by pneumatic spheres (drawing ACA Sbarro)

The benefits of Dual Frame

First of all, weight savings: fewer mechanical elements are needed for the "suspension", and the composite hull is lighter than conventional materials. Of course, this weight saving does not come at the expense of safety, nor does it lead to cost price inflation. The weight of a complete car equipped with the Dual Frame system varies from 800 to 1150 kg, depending on the level of equipment chosen. By way of comparison, a Ferrari 599 GTB Fiorano officially weighs 1700 kg: that says it all!
Handling is progressive. As we have seen, the pneumatic spheres adapt the car to the driving style (sporty, comfort) and the road (low position on circuits or freeways, high position on rough roads, plus all the intermediaries between these two situations).

The mechanical module weighs 500 kg, while the bare composite monocoque weighs just 150 kg. (Drawing ACA Sbarro)

What future for Dual Frame?

Franco Sbarro naturally used the Dual Frame on numerous prototypes, including the two Sbarro Helios, the first cars to be equipped with it. Students at the Sbarro schools also used the Dual Frame for their various projects: proof that this system can be easily exploited. It was to be hoped that this ingenious system, which met the expectations of carmakers, would soon find its way to the general public. But the automotive industry was not interested: only the customers of Franco Sbarro and his students made use of the Dual Frame, which seems to me to be a great pity.

In brief
1- New chassis concept
2- Chassis in two separate parts
3- Chassis used notably on Espera prototypes
Main sources
1- Catalog Sbarro 1991 next step 1992
2- Book "Franco Sbarro / Concept car" by Fabian Sbarro