Mufflers
Buy either sports, semi-racing, or racing. Mufflers are just another option for increasing horsepower.

Brakes
Sport brakes- A must have on your car, your car will then be able to stop faster at higher speeds
Brake Balance Controller- Controls how much pressure will be applied to either the front or  back brakes. The more powerful the front brakes are the more the car will under steer (Ideal for high speed tracks). The more powerful the rear brakes the more the car will over steer (Ideal for tracks like Trial Mountain).

Engine
Performance Chip, Full Engine Balance, Port and Polish, NA Tune-up, Displacement Increase all increase your cars horsepower.

Transmission
Sports- Buy this for non-supercharge engines
Semi-Racing- Use for highly Tuned cars but without high torque, wide power band engines like a muscle car
Full Racing- For tuned engines but cant get above 200mph. By this and change the final drive gear.

• Gear Ratios- Starting with the final drive gear, lowering this setting lowers acceleration, but improves top speed. And just the opposite by raising the final gear improves top speed but lowers acceleration. If you increase the final drive gear to more than five thousand and then put the auto set up all the way to the right than it will give you good revs and top end speed.

Clutch
Heavy-Duty Single Plate- Replaces the normal clutch
Twin Plate- Ideal for high-torque transmissions, improves acceleration. Ideal for muscle cars
Triple Plate- Ideal for highly tuned cars.

Limited Slip Differential
2-Way- Delivers powerful traction during acceleration but makes turning more difficult.
1.5-Way- Provides good traction during acceleration and deceleration and good steering. This is the most common one to buy.
1-Way- Activated in acceleration and is ideal for front wheel drive cars. Causes unstable braking.
Full Customization- If you buy it leave it alone unless you know what your doing or you'll destroy your cars performance.

Flywheel
Sports- Goes hand in hand with a bought transmission. Makes acceleration quicker.
Semi-Racing- Same as the Sports but used in greater tuned engines.
Racing- Same as the other too but also improves deceleration.

Drive Shaft
Carbon Shaft- Improves acceleration.

Turbo
Turbo- Improves cars horsepower greatly.
Intercoolers- Also improves horsepower.

Suspension
Sports- For beginner cars.
Semi-Racing- A step up from the Sports, lets you alter a few things like ride height and springs.
Full Customization- For those serious about changing your ride to the tracks characteristics.

• Spring Ratio- The stiffer the springs the better the acceleration and handling but do just the opposite with tracks like Trial Mountain.
  
• Ride Height- This should be close to the ground. The only reason you wouldn't have the car on the ground is for rough tracks like Trial Mountain.
  
• Toe- A negative setting will help the car turn easier, while a positive will keep the car in a straight line.
  
• Camber & Caster- This will allow the cars wheels to tip inward towards the engine or just the opposite. Basically leave it alone.
  
• Dampers- A softer setting will make the car roll more in the corners while the harder the setting the more the car will become unstable. If your car shakes while on the test course you need to soften your Damper.
  
• Stabilizers- Affect the way you drive around corners. Over adjusting the stabilizers can make the car over reactive on straight always. Under adjusting them makes the car roll more in the corners. So make sure the setting is in between both and similar to the Spring and Dampening ratio.

Tires
Sports- for beginning race cars
Racing Hard- Low grip but primarily used in endurance races to keep grip in the long run.
Racing Medium- A little more softer then the Hard tires. You should use these in the rear with hard in the front for endurance racing.
Racing Soft- Good all around grip. Use these for any race. Once you have the money get these.
Racing Super Soft- Even better then the Soft tires. More grip at a higher price. 
Simulation- Real life tires. These make it harder for cornering, acceleration and deceleration.
Dirt- These tires will only be available to certain cars. Must have these in order to participate in rally events.

Others
Weight Reduction- Lightens the car and improves acceleration.
Racing Car Modification- Improves the car in every aspect. Will not be available to certain cars.

• Down Force- The more powerful the front is the more the car will under steer (Ideal for high speed tracks). The more powerful the rear is the more the car will over steer (Ideal for tracks like Trial Mountain).

Yaw Control System- Controls the distribution of torque to the left and right drive wheels. Raising the setting creates rotational movement in the tires during cornering making it easier. Having to much can make the car spin out.
Active Stability Controller- A high setting stabilizes the car but makes cornering more difficult. A low setting makes cornering easier but diminishes the affect of the system.
Traction Control System- A high setting stabilizes the car by eliminating wheel spin but also debases acceleration. A low setting diminishes the effect of the system but improves acceleration.