Career Mode had been much improved in F1 2018, with one of the best changes being team-specific research & development pathways, which are covered by a "fog of war". This provides impressive replay value to Career Mode and also a lot of unknown factors to the process for new players.
While there are still the minor → major → ultimate quality of upgrades within the Aerodynamics, Chassis, and Powertrain departments, there are also different types of upgrade within each department which creates performance jumps in different ways. To maximise your limited resource points and create a car which suits your own driving style it is important to know how upgrades affect your car.
Within the chassis department you have four different types of upgrade: Brakes, tyre wear, weight reduction and weight redistribution.
The weight reduction upgrades improve the overall responsiveness of the car, aiding acceleration and braking as well as change of directions. The redistribution upgrades continue this effect, providing better balance to allow for more responsive and predictable handling. These upgrades are felt the most around the streets of Monaco and Singapore as well as the twists of Suzuka.
The best upgrades in this department are the brakes and tyre wear ones. The brakes upgrades dramatically reduce stopping distance and overheating problems, greatly improving your out-and-out pace while the tyre wear upgrades can prolong the life of your tyres to an extreme. You can take qualifying tyres deep into the race without having to tip-toe around corners and it greatly reduces the need for two- or three-stop strategies at most tracks. You can also avoid using the hardest compound at a lot of races.
The aero department has four types of upgrades too. Front and Rear Downforce, Drag, and DRS. The DRS upgrade is the least important one of the bunch. While it does increase the efficiency of the DRS, you rarely use DRS in a race. It is available, and vital, in qualifying, but for the most part this upgrade will only have a minimal impact on your overall pace.
The front and rear downforce upgrades improve the efficiency of your wings and the amount of downforce they can generate. The more upgrades you purchase here the more wing angle you can trim from your setup without compromising cornering grip and stability.
The drag upgrades help to improve your top speed. This can be extremely effective at raw power circuits like Monza, Azerbaijan, and Canada where you are frequently hitting 200+ MPH. Combining drag reduction upgrades with brakes upgrades from the chassis department can turn even a Williams into an overtaking machine.
The powertrain department has three types of upgrade: Engine Power, Fuel Consumption, and Energy Recovery System.
The engine power upgrades do impact top speed a little, but not as much as drag, but they improve acceleration most dramatically. Fuel consumption can be a race-winning upgrade, allowing you to run at rich revs for most of a Grand Prix and also letting you severely under-fuel the car to start the race, which helps preserve tyres as well.
The final one is the energy recovery system. These upgrades help harvest energy more efficiently and deploy it more effectively. This is especially good for ERS-hungry circuits like Monza and Azerbaijan where you are unable to run in hot lap mode for the whole lap.
Research & Development Strategy
So how should you allocate your resource points? Well, the most important thing to do is start by purchasing at least one quality control upgrade (which reduces failures) and efficiency upgrade (which reduces costs) in each department. Once you have those, then you should focus on fuel consumption, brakes, tyre wear, and drag upgrades across the three department.
These upgrades all improve the driveability of the car and greatly increase race pace, which is far more valuable than qualifying to your championship hopes. You may not be able to get to these upgrades straight away, but once your branches open out and you can see where they are then these are the ones you should work toward as quickly as possible.