Mods are modifications for your car that will improve its performance and stats. You can have one of each type of mod equipped at any one time. Different mods will be beneficial in different situations and can be changed on the fly through the Easy Drive menu.
Unlocking Pro mods requires the Standard mods to be unlocked first. This is done by placing first in all five of the events tied to the car. Each event has two Standard mods for rewards. If you're having trouble, keep in mind that placing second still unlocks one mod, which you can use to increase your cars stats enough to make the event easier when you retry.
Once a Standard mod is unlocked, the Pro version of it is earned by equipping the Standard mod, and completing milestone requirements tied to it.
These are the mods you'll unlock and the milestone requirements to unlock Pro versions:
Off Road - Drive 5,000 yards off road with off road tires equipped.
Track - Drift 5,000 yards with track tires equipped.
Re-inflates - Hit 5 spike strips with re-inflates equipped.
Burn - Use burn nitrous for 300 seconds.
Powershot - Use Power Shot nitrous 25 times.
Lightweight - Get 60 seconds of air time with lightweight equipped.
Reinforced - Score 10 cop takedowns with reinforced equipped.
Aero - 120 seconds of slipstreaming with aero equipped.
Impact Protection - 2 crash escapes with impact protection equipped.
Long Gears - Drive 10,000 yards in oncoming traffic with long gears equipped.
Short Gears - 25 near misses with short gears equipped.