At present, the semi-space frame chassis type only has a single option for material: aluminum, in the vein of the original Audi A8. However, this seems like a bit of a missed opportunity, for three reasons:
Semi-space frames have been made using a variety of materials. Although Audi’s Audi Space Frame design started out using purely aluminum components, Audi has used a blend of materials for their semi-space frame cars dating back to 2011’s A6. The Audi A6 and A7’s Audi Space Frame chassis is now composed almost entirely of steel.
The A8 wasn’t the first car to use a semi-space frame chassis. For example, the 1983 Pontiac Fiero’s chassis allowed it to use nonstructural plastic body panels - like a monocoque, its chassis was constructed as a single rigid unit, but like a space frame, the chassis alone bore the car’s structural load. GM would later launch its Saturn marque based on the semi-space frame Z platform in 1990.
Unlocking semi-space frame earlier and/or giving it more material options makes it a more viable choice in the campaign. Even though semi-space frame seems better than monocoque at a glance, the player stands to lose a lot if they decide to switch. First of all, there’s no lower-cost option for semi-space frame, limiting its use to premium vehicles. Second, switching means that the player must build new facilities and cope with the loss in familiarity, which poses a significant entry cost. Adding more materials and unlocking SSF earlier would help make it more compelling by making the technology more broadly applicable and giving it more time to break even.
I’d suggest the addition of at least two options:
- Steel/galvanized steel, unlocking in the early 1990s with the Saturn S series. Though slightly heavier than a pure monocoque, it offers better safety for the same material cost and slightly higher tooling costs.
- Mixed materials, unlocking in the early 2010s with the Audi A6. Strikes a balance between aluminum and steel semi-space frame without compromising on safety.
With an argument for one more:
- Glued aluminum, unlocking alongside (possibly instead of) glued aluminum monocoque in 2000 with the Lotus Elise. The Lotus Elise’s chassis, with its nonstructural body shell, could be thought to be a semi-space frame along the same lines of logic as the Fiero and Saturn S series.