- 10 inch wheels - affects packaging for WHUBs, suspension, and frame primarily
- Narrower track (~46", front and rear)
- Smaller wheelbase (60")
- Complete frame redesign - no rear box
- Lower occupant positioning - CG focused
- Lots of downforce
Once again, the focus will be on mass, aero, and mechanical grip. All of these need to be understood on at least a high level to design an architecture, as many of these enablers and decisions will drive packaging. For example, originally I started with a rear box because I thought diffuser design would dictat my suspension points, but with CFD I've found that I can actually get better downforce with a shorter diffuser (more on why that is in another post).
So let's take a walk through how to set up an architecture:
- Pick your basic dimensions, such as wheelbase, track, overall width, etc. Go into these decisions knowing that certain design requirements or trade-offs might forces these dimensions to change.
- Place components that are "architectural" - the components that will be in the same general vicinity no matter what. These part include the engine, wheels/tires, driver, basic frame planes (roll hoops, bulkheads), fuel tank volume, etc.
- Create a vehicle layout - I tend to do this using typical sections. Using these sections, I can throw in background and find out what the constraints are for the system, and keep track of these constraints. That's why in a lot of my models (especially early on) you'll see sketches all over the place.
- For example place the two sprockets, and from that minimum dimension try to match the rear wheel centerline with the drivetrain axis to minimize driveshaft angle. This might dictate engine packaging (in our case it does - it forces the engine forward to a certain position), and understanding what compromises this drives is critical.
- From the example above, the engine more or less defines occupant positioning as well fore-aft in vehicle. In our case, we actually push the driver farther forward, and with lowering the driver, the car gets longer. However, this is a tradeoff between yaw inertia and CG that can be quantified and balanced.
Obviously this is a very high level overview, and there's a lot of work that goes on between the lines. Decisions are made every day, hopefully with data, and communication between the team is key to make sure all involved parties are 1) aware of what's going on and 2) able to offer their perspective on this decision.