What I love about GT3 is full on-deck customization. Sports, Semi-Racing, and Full racing parts fully depend on what you are doing. Normally on some parts like your driveshaft and a few other no name parts you would typically go full racing because of the HP boost and improved performance elsewhere. When it comes to brakes, suspension, tires, flywheels, and clutch it comes down to what are you racing on.
Rally Races use:
- Rally tires
- Sports Suspension
- Triple Flywheel (manual Trans only)
- Semi Racing Trans
- 2 way Limited Slip
Where as an actual racing track would see the use of:
- Racing Tires (I prefer Super Hard on long marathon races and Super Soft on Short courses.)
- Full Customized Transmission for that super speed run
- Triple Plated Clutch
- Racing Flywheel
- Full Customized Limited Slip`
The other items are merely HP boosts. The Brake Controller has an LSD setting you can play with. Once you get back into it, the customizations on all the parts is really down to the core and very useful.
Drivetrains also impact on what your car uses. Drivetrains in GT3 have hidden difficulty levels where FF & FR are easiest to use, 4WD/AWD is somewhat hard to use, and Mid Cabin(MD to my knowledge) is the hardest to customize to use effectively.
If you're using FF which is Front Engine, Front Drive train (where there is no use of a drive shaft), it would be a good drive train to start on. I would go against all out HP Boosts. Since Horsepower is more a ratio of more acceleration to top speed, overpowering your car is easy to do. Most packages involving sports to semi racing are great. There are some RR drivetrains but I haven't played with those enough.
FR is Front Engine Rear Drive Train(the standard of most cars today), these are more customizable, but as a starter package go for more Semi Racing/Full Racing. Some FR cars can go Full racing and some are a very steady and sound investment. Do not bother with NA tuning past 1 or Turbo stage two starting out.
I wont get in the MR since most are high end cars. Just that they go Full racing with Full Customization on parts and where you drop the most coin on.
4wd/AWD will have more a fine tuned mix of HP boosts and stabilizer options. Honestly best cars for off road.