Gran Turismo 4 Tuning

Descriptions for every tuning on Gran Turismo 4

Spring Rate
Spring, together with damper is medium between the tire and car body. Both working together to absorb road irregularity received by the tire to increase comfort and handling. Spring will delay or deviate the force received, damper will dissipate it.
The higher the spring value, the harder it is and vice versa.
Forum argumentation on understeer/oversteer effects.
Many go to the opinion that a harder spring rate sticks to the track more. So when the rear spring rate is harder than the front, it understeers more, and when the front spring rate is harder than the rear, it oversteers more.
Stiffer spring rates also reduce body roll, which in turn increases handling in corners and reduces the need of high degree camber.
Too stiff of a spring rate can mess up a car's handling if the tire is unable to keep contact to the road properly.
If your rear suspension is too soft, your car would have a tendency to slowly drift or spin out in mid corner, but it will be easy to control. If your rear suspension is too stiff, your car would have a tendency to snap or slide at mid corner bump which is difficult to control.
Set stiffer spring rate for heavier part of the car. This will help midcornering ability of the car. Car that tend to tail slide during cornering caused by heavier rear will be more tame using stiffer rear spring rate or softer front spring rate. Car that tend to go straight during cornering caused by heavier front will be less understeer using stiffer front spring rate or softer rear spring rate.
Ride Height
Car with lower ride height has less body roll because of lower center of gravity, this will improve handling and corner grip.
Setting ride height too low can cause the suspension to bottom out, which can interferes with car handling. In some cases the chassis of the car can makes contact with the road, which can be notice easily as it usually create some sparks.
A lower front ride height will make the car more oversteer, and a lower rear ride height will make the car more understeer. This happen on the first stage of cornering, corner entry, where car body being sway to the side.
If ride height is too low and result in suspension bottoming out, the side which it's suspension bottoming out will loose traction suddenly on later stage of cornering, creating sudden understeer or oversteer in mid corner. To prevent this from happening, increase the ride height of the affected side.
Damper
Real life reference for car handling
Dampers dissipates force received by the tire. Dampers will prevent the springs from continuing to bounce after the tire travels over a bump. They also affect the speed at which the weight transfer is applied to the contact patch of the tire.
Bound is when the wheel absorbs the bump, Rebound is when the wheel goes back down after absorbing the bump. So it's best for the Rebound value to be higher than the Bound value. This allows the car to absorb impacts but also returns the contact patch to the pavement as quickly as possible.
Lower number values mean less damping effect - more bouncing of wheel relative to chassis.
A lower value makes the car less responsive to steering inputs, and can stabilize the car at high speeds. However, at extreme softness the chassis movement may become undercontrolled on rough pavement.
Higher number values mean more damping effect - less bouncing of wheel relative to chassis.
A higher value makes the car more responsive to steering inputs, and can stabilize the car's transitional phases. However, the suspension may not be compliant enough to absorb bumps, unsettling the car on rough pavement.
It's best to adjust the dampers to the weight distribution of the car - more damping for heavier parts. So for FF's, make the front dampers a substantially higher value than the rear.
Damper have most influence at car pitch change, like when applying throttle or lifting off throttle.
If the car feel understeer on lift off throttle reduce front bound or increase rear rebound. Likewise when the car feel oversteer on lift off throttle increase front bound or reduce rear rebound.
If the car feel understeer when applying throttle increase front rebound or reduce rear bound. Likewise when the car feel oversteer when applying throttle reduce front rebound or increase rear bound.
Camber
During cornering, the car body will lean to the corner outer because of it's weight, called rolling. Stabilizer, spring rate and ride height setting can be used reduce this, but sometime it won't be enough. During this rolling the tire which attached to the car body create an angle too, making the tire do not make flat contact with the road anymore. The goal when tuning camber is to make the tire make contact with the road as flat as possible at critical point of the track corner. Doing this correctly can make the car passing those corner at a faster speed.
Camber in GT4 is negative angle. More camber value means more negative camber.
Unlike real life, in GT4 the amount of angle that the tire make during cornering is the same as the angle of the car body roll. By measuring how much car body roll happen during cornering, we can estimate how much camber angle needed.
The optimal camber value for grip racing is different for each car, and can change when other suspension settings are changed.
Increasing the front camber does not always result in more front grip, especially if your car has little body roll.
There is no formula for camber, its better to start from scratch and see what each change does.
Higher than normal value can be used to make the car lose traction more in corners and on straightaways, so if N1 tires aren't slippy enough to drift, using excessive camber can help it. (Not a recommended method of tuning)
Using high camber value can increase tire wear
Toe
-4 is toe out, +4 is toe in.


Positive rear toe can make the car drift longer, more stable and easier to control, and on some cars it can give a little more traction to help acceleration.
Negative rear toe makes exiting and entering drift easier.
Positive front toe makes the car more stable on the straights, but it doesn't handle as well.
Negative front toe makes the car more responsive to steering, and can help with handling, but the car becomes more unstable.
Excessive toe angle can slow down a car and can cause more tire wear.
Stabilizer
Also known as anti roll bar or swaybar, it can have the value between 1 and 7.
High setting will make left and right wheel less independent, but with benefit of less body roll.
Tuning stabilizer involve in balancing between car roll and left and right wheel independencies.
Higher front value generally makes the car understeer more, it is good for a car that has corner entry spin tendencies (MR and RR).
Higher rear value can help FF car to turn better.
Stabilizer has most influence at mid corner. Because the stabilizer try to hold left and right suspension together, using high value will reduce the left and right suspension independency. This will make the side with stronger stabilizer loose traction more. At mid corner when the car being force to roll by centrifugal force, the side with stronger stabilizer will resist the force more, resulting in less traction for that side. This is looks apparent on MR, where you see the car rear get gradually loose traction on mid corner. Increase the front stabilizer or reduce the rear stabilizer to cure that.
Use stabilizer appropriately, use in combination with other suspension setting. Too strong will make the car unstable (bounce left and right) in road irregularity, especially on corner. Too soft will make the car roll too much and reduce traction.
Brake Balance Controller
Scaff's BBC Guide thread
BBC control how much force applied to the front and rear brake. By increasing BBC, we increase braking force. Unfortunately, if we set braking force too high, the GT4 always on Antilock Braking System will interfere and can make the braking distance increase. There is an optimum BBC value, sometimes a combination of spesific front and rear value, which varies for each car that gives the best braking distance.
Carefully tuning front and rear BBC value can help correct handling while braking and reduce the braking distance.
Transmission
Transmission is a gear combination that works to deliver power from engine to the tires. Correct gearing can make the car accelerate faster and has high speed too. It is a good thing that most car in GT4 has modifiable gearing. We can make an already fast car even faster.
Auto configuration feature can help us create a gear for spesific speed. You will see on some setting mentioned using "auto 16", this mean we have to change the auto number to 16. If the number is already 16 you have to change it to 17 or 15 and then to 16. If final drive not mentioned, it usually mean you use auto at default final drive. If final drive mentioned, you need to change the final drive before changing auto number.
auto configuration can give the same top speed for the same car type, like for example auto 1 at 5.000 final drive will give top speed of 150mph on most LMP Car.
Long gearing (low gear ratio and low final drive ratio) can reduces tire spin, it have higher top speed but also lowers acceleration.
The key to gear tuning is matching the gear to the corner speed or straightaway speed.
New gear ratio * new final drive * new speed = old gear ratio * old final drive * old speed
Tranny trick = move final gear ratio to maximum value, move auto to 25 and then to 1, and finally, move the final drive ratio to a value that makes the car top out at the end of the longest straight.
Closer gearing can be created by lowering the first gear ratio, raising last gear ratio, and adjusting other gear so it will look like "\".
Other way to make closer gearing is by using the tranny trick, which can reduce the distance between 1st and last gear more. In order to get the needed speed, use slight variation, like a lower final drive before using auto (if the resulting top speed is too high) or raise auto number (if the resulting top speed is too low).
If both methods above are combined, the result is that your gearing will be very close.
Close gearing can be very helpful for cars with a steep power curve.
LSD
LSD works by distributing power between wheels, that is only the rear wheels on an FR drivetrain, front wheels on a FF drivetrain, etc.
At a lower value, the power goes to the wheel that is easiest to spin, so you may have just one tire spinning at a time, which lowers traction greatly and reduces acceleration.
At higher values the left and right wheel will have low speed difference, LSD will try to keep both wheels rotating at more similar speeds. This makes the individual tires less likely to spin, so the "slip" is reduced. This will not, however prevent both tires spinning (loss of traction) which often occurs with some high power cars. High LSD values can make the car understeer more if used set too high.
Initial LSD affects the car behavior when not braking or accelerating, for instance when cruising or throttle lift off.
Accel LSD affects the car behavior when accelerating.
Decel LSD affects the car behavior when braking.
The LSD value seems multiplied by how much G's the car can pull on acceleration or braking. (2G's = 2 times the force of gravity.)
ASM
ASM pretty much applies the brakes or when it senses understeer or oversteer. The higher the number it is, the more sensitive it is (ie setting ASM Understeer at 10 will get rid of more understeer than setting it at 3). Since ASM applies the brakes when it senses an unwanted handling, it slows down the car. So it's best to keep it at a minimum, and if wanted, none.

Since the handling may be unwanted after the removal of ASM, the best way to cure it is to control the throttle. When it is understeering in corners, let off the throttle some so it will go through the corner more easily. And if your car has a tendency to oversteer when hitting the throttle out of corners, ease into the accelerator, so your rear wheels won't spin and make you oversteer.

Of course, in some cases ASM is a bit faster, such as helping go across a sweeper on the track more easily, using a normal controller. But in most other cases, it will slow down the car, resulting in a few extra seconds on your laptime.

When you tune your car, always decide wether you will use ASM or not. Car handling can feel very different between using and not using them. If possible always try to tune with ASM off, it will be easier to know what is wrong with the car. If you can drive the car without ASM, you can improve your time more.

TCS
TCS works to improve handling by reduces the wheelspin / slip during acceleration by slowing down the wheel (using the brakes or by lowering engine power). Unlike real life, this is not the same as launch control in some exotic car, in GT4 using TCS will reduce acceleration at any speed and should not be used to increase acceleration.
TCS can help control car with high power.
Higher TCS value do not always mean more control, using TCS:1 is usually enough for most cases.
You can modulate the throttle so you won't need to use TCS, and it will make your car accelerate faster.
Max Speed Tuning
The key is to get to a wheelie setting as close as possible but without making the car actually do a wheelie.
Wheelie = the front tire lift by the wind, and it results in more acceleration, and can make the car go faster than normal.
Wheelie trick = low spring rate, high front ride height, low rear height, low front downforce, high rear downforce, and plenty of power!
Don't hit the rev limiter.