Suspension and Drivetrain
Suspension and Drivetrain

Suspension
The suspension set up of each car affects the way the car will handle, turn, roll, flex and even the traction of the vehicle.

Springs and Coil Overs-Replacing the OEM springs will lower the center of gravity and reduce the body roll. The two choices you have are either Springs or Coil overs. Springs are usually cheaper, but are not adjustable. Coil overs allow you to adjust the height the vehicle rides out, where as springs are determined by the weight and manufacturer specifications. The down side with coil overs is that they usually do not last as long, and if one coil over is riding at different height, one will be at a higher stress level. It is often a wise idea to install a set of Caster Camber plate with either of these to insure proper alignment and improve the caster geometry. The Caster plates work nicely with a strut tower.

Struts or Shocks-Struts and shocks are essentially the same thing, struts are usually on a car, and the shocks are usually on a truck. Replacing these with firmer ones will give the vehicle more control in cornering and wheel motion. Many aftermarket units allow the adjustment of the comfort level. This allows you to choose whether you would like a rock hard ride, or a soft smooth ride.

Strut Tower Braces-Strut tower braces stiffen the body frame, which stabilizes the suspension during hard cornering and reduce body vibration. Not an expensive modification, but it does make a difference.

Control Arms-Control arms improve traction, stability, and side to side travel under hard acceleration.

Sway Bars-Swaybars keep the vehicle from rolling during corners, eliminates under steer, and increases the vehicle's cornering speed.

Sub Frame Connectors-Subframe Connectors help eliminate body twist and strengthen the suspension supports.
Traction Bars-This will greatly improve traction problems, and in a front wheel drive vehicle it will eliminate wheel hop.

Wheels-Wheels are not only an aesthetic modification, in fact they can be one of the most beneficial factors to your entire car's set up. Usually the stock tires are quite heavy, and narrow. Usually they don't even look good. By replacing them with aftermarket rims which are lighter, and wider you increase the performance. The heavier the wheel is, the harder it is to get that tire rotating. The wider, and taller the tire is the more traction you have at all times. This extends to a certain point though, if you get a tire that is so large that it weighs too much, this will decrease your acceleration. Also, if you have a limited sleep differential large wheels will tear your spider gears apart because there is no give in the axles or differential. Larger tires will also cause your car to loose much of it's cornering ability. So try to pick a nice equilibrium between the sizes.
Tires-Tires are also one of the most beneficial factors of a car's handling and traction. Each tire will have a different design and tread pattern that will respond differently. Lower profile tires are usually agreed on the best performance, but this does not always hold true. Because the tire is not as tall, it is lighter. This is also a bad thing because this causes the rim to become much more prone to bending because there is less side wall to absorb the strain from the weight. Lower profile tires also provide a firmer ride, with much less give while the tires with the large side wall provide more comfort and far less road noise.

Drivetrain
The drivetrain consists of the assembly that transmits an engine's rotary motion to the wheels. By modifying this, you can gain more traction, a more efficient means of transferring the power to the wheels, safety, and the ability to contain and transfer more power.
Clutch-The clutch disconnects the engine from the transmission, to allow the vehicle to brake, drop the rpm's, or change gears and then allows the engine and transmission to resume contact and turn together at a new speed. By replacing this with a stronger, more firm clutch the transfer of power becomes more efficient. The stronger clutch also means that the transmission will be able to hold more power than it previously had. This will usually result in more pressure to push the pedal in, and sometimes the shifting is not as smooth.
Flywheel-The flywheel is a heavy wheel that uses it's inertia to oppose and moderate any fluctuation of speed in the clutch, transmission and crankshaft. The flywheel keeps the engine moving as well once it has been started. You can replace this with a stronger and lighter flywheel which will allow the engine to rev faster and transfer the power more efficiently. With a turbo vehicle, this is not always a wise modification. The flywheel removes a lot of load of the engine, and a turbocharger will under work under load.

Axle-The axle transfers the power from the differential to the wheels. This works by running a splined shaft directly into the differential. You can upgrade the axles to stronger ones so that the power does not tear apart the axle or cv joints.

Driveshaft-The Driveshaft runs from the transmission to the rear differential. By rotating into the gears, the power is transferred to the axles. You can replace this with a lighter, more finely balanced driveshaft to allow faster acceleration due to the weight loss.

Differentials-An aftermarket differential may be installed to reduce wheel spin. There are two different types all in all. A clutch type and a plate type. This works by sending power to both axles rather than just one, diving the power into two parts.