Maximizing corner exit grip (Minimizing under and oversteer at full throttle or the edge of wheelspin) while not impairing your performance on the rest of the circuit (i.e. straights)

Optimizing corner entry balance while not impairing corner exit grip. (Making sure you make it safely through the corner)

Tuning the car based on driver preference; you can have the fastest car in the world, but you'll never be able to be the fastest in it unless you're both comfortable and confident within the car.

Front Wing
The front wing helps the car to gain downforce at the front end. Increasing it's value will
eliminate understeer at medium/high speeds. But It will increase drag thus slowing you down
on straights. Decreasing it's value will make the car more stable at medium/high speeds and it
will decrease drag increasing your speed on straights. You can also gain downforce by lowering
the car

Rear Wing
The rear wing produces downforce at the rear end of the car in the expense of more drag.

Increasing the value will make the car more stable at medium/high speeds but you will lose top speed

Decreasing the value will make the rear of the car more lively but you will gain top speed.

Longitudinal meaning:running lengthwise rather than across.
Lateral meaning:of, at, towards, or from the side or sides.

Camber
Increasing the value will make the wheel gain negative camber. More negative camber
gives more turn in and lateral grip but less longitudinal grip while braking or accelerating.
More camber also raises tire temps.

Decreasing the value will make the wheel lose negative camber. Less negative camber give less lateral grip but also more longitudinal grip while breaking or accelerating. It also lowers tire temps
spreading them more equally.

Toe
A negative value means the wheel, as seen from above, looks towards the outside of the car.
Gives faster turn-in but also instability under braking, higher tire temps and less mid-turn grip

A positive value means the wheel, as seen from above looks toward the inside of the car.
Gives slower turn-in but more stability under braking and higher tire temps.

A zero value gives higher top speed and lower tire temps

The damper stops the spring oscillation(movement back and forth in a regular rhythm.)
Damper bump creates a force to slow the speed of the suspension in compression (bump)
when slow movements occur, primarily on weight transfers (roll, pitch)

Bump
Higher values at the front make the car more reactive giving better feeling and precision,stability under braking
but also higher tire temps and wear
Higher values at the rear make the car more reactive giving better feeling and precision but also gives more oversteer under acceleration or at the moment you release the brakes entering a turn

Lower values at the front make the car more predictable but slower in reactions, less precise
and less stable under braking but It lowers tire temps and wear
Lower values at the rear make the car more predictable but slower in reactions, less precise
when drifting but also more traction and stability the moment you release the brakes entering a turn.

Rebound
Higher values at the front make the car more stable and fast on changing direction (ex. chicanes)
Higher values at the rear make the car less stable under braking and initial turn-in, but also much more agile on slow turns that need the whole car to rotate.

Lower values at the front eliminate understeer under acceleration but it also makes the car slower to change direction.
Lower values at the rear make the car more stable at initial turn in but can provoke inertia movements of the rear end on chicanes and fast direction changing

Diff power
When a wheel is spinning under power it loses grip. A locked diff will transmit more power on the
non spinning wheel thus aiding traction but also changing the handling of the car.

Higher values will aid traction until grip is enough but then will provoke both driven wheel spinning.
This will give oversteer to RWD cars and understeer on FWD cars under power.

Lower value will give less traction letting the spinning wheel to continue spinning. Makes the car more stable under power but also makes you lose time and overheat the spinning tire.

Diff Coast
When braking or coasting the locked diff will try to keep both wheels at the same speed. This can change the handling of the car.

Higher values make for a more stable car under braking but also cause understeer.

Lower values will make the car less stable under braking and turn-in but also make it more agile and willing to rotate

Diff Preload
Keeps the diff locked until torque difference is equal to the value indicated. Then the lock becomes the one in power/coast.

Zero or low values make the car agile in the initial turn-in but can also make it nervous or lose traction if driven very abruptly

Higher values can make the car more stable and give traction but can also overcome the diff power and coast settings making the car feel very tight and resistant to turning.

Gear ratios are the number of teeth on two meshed gears. For example, 1st gear will be the smallest gear on the layshaft/countershaft and will mesh with the biggest gear on the mainshaft. If 1st gear on the layshaft has 10 teeth and 1st on the mainshaft has 30, their ratio is 10/30. When you change ratio's you change individual gears, so they're either bigger or smaller, hence you get either better acceleration/low top speed in that gear or vice versa. So 9/25 has better acceleration, whereas 16/32 would have a higher top speed (due to the gear reduction effect) as the difference in size between the two gears is smaller, so the torque increase through the gears is lower.

So basically the numbers and the top speed/acceleration have an inverse proportion.
High number = High top speed, worse acceleration
Low number = Low top speed, better acceleration

You should do a couple laps on totally different tracks (ex. Monza and Monaco) to get what I am saying.

Spring Rate
This is the spring force multiplied by the install ratio of the suspension.

Increase the value to stiffen the suspension and get a more direct handling with fast reactions.

Decrease the value to soften the suspension and get a more slow and predictable handling.

You may think the stiffer the suspension the less grip you get but this is not the case and it depends on suspension geometry and other design choices. As usual try to find a compromise via trial and error.

Ride Height
Modifies the length of the damper rod and subsequently the ride height of the car.

Keep in mind that ride height also varies depending on the wheel rate values, tire pressures, fuel load and the travel/rigidity of the bumpstop packers.

Anti-Roll Bars
Increase the value to make the front/rear end roll less and gain stability,precision and fast turn-in. You might lose some grip on the front end but it's not always the case depending on the suspension geometry.

Decrease the values to make the front/rear end roll more. You will have better mid-turn grip but you will lose precision and agility and a slower turn-in.

Keep higher values on tracks with lots of bumps and kerbs to aid stability.

Travel range
This is the suspension travel before it hits the bumpstops.

With a higher value the suspension has more travel before it eventually hits the bumpstop.

With a lower value you hit the bumpstop earlier thus blocking suspension travel.

Check the bumpstop rate to help understand what happens when the suspension hits a bumpstop.

Bumpstop rate
Packers or bumpstop rate

This is usually a rubber spring before the actual end of the suspension range. It's basically an extra spring that starts working when the suspension is compressed enough to hit on it.

Increase the value to limit the suspension travel after it hits the bumpstop. Makes the car more reactive.

Decrease the value to permit a bit more suspension travel after it hits the bumpstop. Makes the car more predictable.

Brake power
Modifies the power of the brakes in order to avoid the locking of the wheels

A value of 100 defines the maximum brake power and equals to shorter braking distances with an higher chance of locking the wheels.

When the value is less than 100 the chance of locking the wheels is lower but the braking distances get longer

Brake bias
Changes the amount of braking power towards the front or the rear of the car.

More foward bias makes the car more stable but also can lock the front tires.

More rearwards bias makes the car more agile and willing to rotate during turn-in but also less stable and easy to spin.

It's generally a good idea to set the bias as rearwards as possible without locking the rear tires.
I would also recommend setting a bind to adjust the bias on your steering wheel/controller on the go.

Cold Pressure
Increasing the tire pressure will give more precise steering, higher top speed and maybe lower tire temps if you don't push the car too much but it will make the tires slide earlier if you overdo it.

Decreasing the tire pressure will give more traction and grip but also less precision, lower top speed and more heat.

Take track conditions (heat,etc.) into consideration while adjusting tire pressure.

Tire Types
On most cars you will have more than 1 tire option.

Choosing tires especially on MP races can mean the difference between winning and losing. Choosing harder compounds will mean you will be able to race longer for slower while softer compounds will mean you can race faster for shorter.

Tire options also make a difference on hotlap mode especially on longer tracks (Spa,Silverstone,etc.)
You may think that the softer tires would be the best choice since pit stops don't make a difference but especially on Silverstone where load on your tires aren't equal on both sides causing them to overheat if you push too hard. So to keep pushing hard you might find yourself switching to medium tires.

Loss of control
1)Move brake bias forwards
2)Decrease slow damper

Front tire lock
Move brake bias backward

Car pitches too much
Stiffen front springs

Nose scrapes the floor
1)Increase ride height
2)Adjust bumpstops
3)Stiffen front springs

Excessive locking
Reduce brake pressure (power)
(Be careful)


Understeer
All Speeds:
1)Adjust front tire pressures
2)Soften front ARB
3)Increase front toe out
4)Decrease diff coast
5)Soften front springs

Mid-High speeds:
Reduce rear wing angle or Increase front wing angle

When Braking:
Move brake bias rearwards

Oversteer
All speeds:
1)Adjust rear tire pressures
2)Stiffen front anti-roll bar
3)Decrease front toe out
4)Stiffen front springs

Mid-High speeds:
Increase rear wing angle or decrease front wing angle

Lift-Off Oversteer
1)Increase diff coast
2)Increase pre-load value

Understeer
All speeds:
1)Stiffen rear ARB
2)Increase diff power locking
3)Stiffen rear springs

Mid-High Speeds:
Reduce rear wing angle or Increase front wing angle.

Oversteer
All speeds:
1)Soften rear ARB
2)Decrease Diff Power locking
3)Soften rear springs

Mid-High Speeds:
Increase rear wing angle or decrease front wing angle

Car bounces during weight transfer (turning)
When braking,accelerating and turning:
Increase slow damper setting

On bumps/curbs:
Increase fast damper setting

Tires overheat
All over:
1)Increase pressures
2)Decrease toe value

Tires can't heat up
All Over:
1)Decrease pressures
2)Increase toe value

Low top speed
1)Reduce wing values
2)Increase tire pressure
3)Reduce fuel

Hopefully I have teached you something.