PRO kits are great ways to extend your vehicles' performance even further than it can at MAX level. These cards are found all over the place. You can get them from a multitude of boxes, from winning them in Time-Limited Events, R&Ds, EDDs, Championships, Moto Blitz seasons, and sometimes can even be found in Mastery. Every upgrade rank requires more cards, sometimes more rare than others, and some require a ton of cards (HTT Plethore LC 750 (with 170 cards)). Around 95% of the cars require FIVE (5) different PRO levels for four statistics:
Since the F1 cars (M14A, MP4/8, MP4-25, MP4-31) are PRO-only cars, they require 10 PRO ranks to PRO a single statistic.
For cars, PRO kit cards consist of Tires, Suspension, Drivetrain, Exhaust, one of three different techs*, and one engine**. These can vary in quantity, and they can clout quite a hefty price tag. Certain beginner cars like the Dodge Dart GT, only require ONE PRO kit level to PRO one category.
For bikes, PRO kit cards consist of Bike Tires, Fork Tubes, Transmission, Bike Exhaust, one of four different techs***, and one of the two bike engines****. Again, can vary in quantity going up the PRO ranks, and they can clout quite a hefty price tag. Although bikes require 10 levels to upgrade to MAX, they only require 5 PRO ranks before it earns the coveted PRO rank.
Upgrade all the stats to PRO, and you'll get the PRO badge in the garage, located next to the MAX symbol. PRO kits are available all the time, and don't require you to MAX the car in order to unlock the separate performance section.
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If you have seen the asterisks (*) above, that is because there are multiples of that card.
* - Initial Tech (C), Early Tech (C), Mid-tech (R), Advanced Tech (L)
** - I4 (C), I5 (C), I6 (C), V6 (C), V8 (C), Forced-Induction V8 (L), V10 (L), V12 (L), V16 (L), W16 (L), F12 (L), F6 (L), Electric (R), Hybrid (R), Rotary (L), Serial Racing Engine (R), High-Grade Engine (R), Custom Racing Engine (L), Exceptional Engine (L)
*** - Common Tech (C), Rare Tech (R), Pro Tech (L)
**** - Four-Stroke Engine (C), V-Twin Engine (C)
Key: (C) = Common (R) = Rare (L) = Legendary
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As you may already know, the upgrades will get more expensive as you go. The higher-up the car is, the more cards it will need.