Better Tires give the Drifter Bike more grip on and off road. Tire I costs 840 credits at Trust level 1 and Tire II costs 840 at Trust level 2. They make the bike easier to handle on dirt and in chases.
The bike slides less on dirt and gravel and corners better in a chase. Fewer crashes also means fewer repairs.
It is a mid-priority buy. Pick it up after the fuel tank and engine if off-road handling bothers you.
Derelict Vehicles
Derelict Vehicles are the dead cars and trucks across Oregon, and nearly all of them can be searched. They give crafting parts, ammo, fuel and Medkits depending on the type. Loot them as you ride, and use them as cover.
Engine
The Engine upgrade raises the Drifter Bike's top speed and acceleration. Engine I costs 1,200 credits at Trust level 1, and higher tiers add durability. It is one of the first parts worth buying, since speed is how you escape Hordes.
Exhaust
The Exhaust upgrade quiets the Drifter Bike so you can ride near enemies without being spotted. Exhaust I costs 600 credits at Trust level 1. Buy it early if you like stealth approaches to camps and nests.
Forks
The Forks upgrade helps the Drifter Bike absorb damage. Like the frame and rear suspension, it means fewer stops to patch the bike with scrap. Buy it after the speed and fuel parts.