¶ Overview
Driving around the track, performing an overtake, and even other cars pitting when you're on 
Durable Tires - all these actions earn you experience points (XP), which you can later use to upgrade your car.
¶ Earning XP
¶ Driving Around the Track
Each track consists of many invisible checkpoints (not to be confused with sectors). When your car drives through one, you receive a certain amount of XP that depends on the XP Gain modifier's value and your 
XP Gain upgrade's tier. The higher they are, the greater the multiplier that gets applied. You can increase that amount even further by putting on 
Experimental Tires, and selecting 
Sensor Quality cards.
¶ Overtaking
When your car performs a successful overtake (whether by winning an on-track battle or passing a car in the pit lane), you receive a base 350 XP bonus that gets increased as you upgrade your Sensor Quality, but also if you have 
Fast Tires equipped.
Overtaking bonuses are applied per car, not per maneuver. In other words - the total XP bonus you receive for overtaking many cars at once is the same as the total bonus for overtaking each one individually.
¶ Having Durables When Others Pit
When you're running on Durable Tires and a car comes into the pits, you receive a bonus that also increases along with your Sensor Quality upgrade's tier. Just like the overtaking bonuses, they're applied per car in case multiple pit.
¶ Levelling Up
At the start of the race, you need to gain 1500 XP in order to be able to select your first upgrade. From here onwards, the number of points you're required to score goes up by 25 if you're on Experimental Tires, and 50 otherwise.