Everything you've learned, on one screen: gearing from Stage 02, regen from Stage 03, power management from Stage 05. Pick a terrain, build a setup, and beat the engineers' target time.
Each terrain rewards a different compromise. The terrain brief is your engineer's hint.
Beat the target to take a virtual stage win. Your best time is saved to the timing sheet.
Deep sand wants force, frozen ground wants restraint, rainforest mud wants recovery. Every slider you moved is a trade against the others. Engineering is choosing which compromise wins on this map, today.
Gear taller and the motor works harder: more heat, more derating risk. Cap power and the battery lasts: but the launch suffers. Six stages taught you six parts; a race car is where they all argue with each other.
You found the better setups by running, reading the time, and adjusting. That loop: test, measure, change one thing, is the entire job of a race engineer, and of most engineers everywhere.