another helpful link to check out is Web's Sway Bar & Strut Bar thread that information can compliment a lot of the things I'll explain here.
I'll do my best to keep things easy to understand and tC specific, but even though I'm being tC specific, this information can apply to almost any car.
The tC when you buy it off the lot with no changes made to the suspension, you'll notice the ride although being pretty nimble, has too much body roll and lean to provide a sporty ride.
Most cars have this problem stock unless they are specific sport performance vehicles. The tC (Touring Coupe) is a hatchback coupe, not a sports car. Engineers have placed softer springs and sway bars to provide a softer comfort balance than sports performance.
PREFERENCE FOR A SPORT RIDE
Most consumers prefer a comfortable ride instead of a firm or harsh ride, that is why engineers place a strong emphasis on comfort. This trend is slowly changing as drivers push for higher top speeds and an aggressive style of driving.
The ideal sports ride would be a vehicle that does not flex or bend, the term most commonly used to describe this style of ride is rigid
All vehicles flex and bend as you turn, go over bumps or do any style of driving, no vehicle is 100% rigid, if it were, you'd crack your car in half just trying to get over a pothole
There are a few simple upgrades you can do to make the vehicle rigid and well balanced to provide a sportier ride than stock
INTRODUCTION TO MODIFICATIONS
^image of TRD rear sway bar
There is a lot of misunderstanding about a sway bar and what it does for your car. If you complain that your car leans or rolls too much, that is mainly due to your sway bars
How can you tell if your car has too much body roll or sway?
Go to an area with little or no traffic or an empty parking lot and drive about 10 mph and swing your steering wheel from side to side at about 10-15 mph (do not do this at high speed) if your car rocks like a boat, you've got too much sway
There are kits you can buy that include a front sway bar, but even a rear sway bar alone is very effective.
HOW THE SWAY BAR WORKS FOR YOU
It's a piece of metal... a bar... as a matter of fact, it looks like something you'd add weights to at the gym to do power arm curls...
this metal bar connects one side of the car to another to reduce twisting... yes when you were swerving your car side to side at 10 mph, the rear of your car was twisting and bending.. a sway bar will reduce this twisting to keep your body and wheels firmly planted to the ground.
Even if your car is front wheel drive, it's important to reduce this twisting at your rear because as your rear is rolling and twisting, that force is carried to the front of your car and can affect the traction of your front wheels. Since most cars steer at the front, a majority of this twisting moves to the rump of your car.
Most people that know suspensions will agree that a harder sway bar will be a very worthwhile suspension upgrade and I'd agree as well. The difference is almost night and day.
SPRINGS & SHOCKS
also called lowering springs, most sport performance springs will lower your car to provide a lower center of gravity, but more importantly, these springs are stiffer
It all goes back to the rigidity thing.. soft springs are like gym shoes with trampoline like bounciness to them...
okay.... imagine trying to play basketball with shoes that bounce way too much... it's not going to help you jump higher if you have loose bouncy soles... try and dribble around someone with bouncy loose shoe bottoms... if you tried to slam dunk, most of the force from your leg muscles would be absorbed into the shoe bottoms, they'd be comfortable to walk in, but it'd be hell trying to do any kind of sports... think of springs for your car in the same manner
As you lean into a sharp turn at 30 mph, a lot of force is moving into the springs and they compress, eventually the springs will decompress the speed is compression and decompression is controlled by your cars shocks
Think of springs and shocks as a team that work together, without shocks, every time you'd hit a bump your car would bounce and not stop bouncing for a very long time.
Let's go back to the analogy about playing basketball with bouncy soles, your leg muscles would be the shocks and your springy bouncy shoes would be the springs. With super bouncy shoes, your legs would have to work a lot harder to control your body from bouncing your body flat on your face
I cannot go into detail about all the different types of springs, but keep this in mind, the lower your spring, the longer the shocks have to hold their compression, a mild drop is usually okay because it doesn't go beyond the shocks range of compression/decompression. You can always go extra low, but keep in mind your normal shocks will have to work a lot harder
Specialty shocks or performance shocks have a difference range of compression/decompression, many are designed for short springs and have a stronger resistance to compression/decompression to provide an even greater feeling of firmness.
Some shocks/springs are sold as a complete adjustable kit so you can adjust compression/decompression of the shocks, I will not say one is better than the other. You should buy shocks and springs according to your needs. A fully adjustable kit is normally an overkill for daily driving and mild street driving
WHY DO I NEED LOWER SPRINGS
I wouldn't say you need to have lower springs, but it can enhance your ride by keeping your car lower to the ground. Keeping a lower center of gravity can further reduce the lean of your car during sharp maneuvers. Having extra stiffness in the springs can prevent your car from bouncing too much when you need to have control, just remember the bounciness basketball example.
If you think it'd be a good idea to have rock stiff springs, just imagine walking around with shoes made of granite/rock, it's just a bad idea. You need some flex in your suspension to have a good balanced ride.
On top of all that, lowering your car looks really good
BRACES/STRUT TOWER BARS
This is pretty easy to explain, the front strut tie bars, rear strut braces, c-pillar bars and everything else you can think of, have one goal in mind! RIGIDITY!!
These thing work a little by themselves, but they are further enhancements to everything we mentioned above
Should you get braces and bars? Yes
As I said before, it's not as effective by themselves, but these modifications can enhance your ride, by further reducing twisting bending forces through your car.
Over time, as you acquire many miles on your car, all the bending and flexing can takes it's toll and if you're really perceptive you may notice your ride not feel as solid as before.
If you get into a really old ride (15-20 years old) you'll really understand lack of rigidity.
New cars have new steel and feel pretty rigid... because they're new.
The goal of rigidity is keep the car solid so you can keep your tires firmly planted to the ground, since most of the twisting happens at points where the body connects with the wheels, most ride enhancing parts tighten those areas where the body meets the wheels.
Everything we mentioned above means nothing without tires, if you really want to make the biggest impact on performance and driving as well as safety, you MUST start with your tires!
I can't stress this enough, if you complain that your car drives like crap in the rain, it's your tires
Want to take those turns a little faster? You'd better upgrade your tires!!
I hope you've found this information helpful, it's not meant to be an end all point of information, but a guide to help new users understand some benefits to suspension upgrades.
Extra performance is nice, but it means nothing if you can't put that wheel horsepower to the ground and keep it there.