Reference
Upgrade Order Cheat Sheet
The order to buy stage upgrades in so that every purchase improves your elapsed time immediately.
General order
- Tyres (grip first, always)
- Transmission
- Engine
- Turbo or intake
- Nitrous
- Body and weight reduction
Why grip first
Power you cannot put down does nothing. If the car spins off the line, engine upgrades make the problem worse.
Exceptions
All-wheel-drive cars can move engine ahead of tyres, because launch traction is rarely the limiting factor.
When to stop
Stop at stage 5 across the board before you touch fusion parts. Stage upgrades are always the cheaper performance per unit of currency.