Tunability:
The tuning in-game is very restricted, only having the gearbox the only tunable option. By adding more tuning options such as;
Adding tunable spring compression and rebound rate, where you can tune the rate of your suspension’s compression (how fast it compresses) and rebound (how fast it extends and return to its normal position).
Reworking the gearbox tuning to tune the gear ratios on each gear, you can make the gearbox short on the first few gears, helping acceleration, and longer on the rest of the gears, helping top speed.
More upgrade options:
Just simple suggestions like;
Forged engine block and internals, making the engine withstand more compression which means more power
Carbon Ceramic brakes, making the braking power more powerful.