I just want to clarify:
Four wheel drive only distributes acceleration forces due to engine output to four wheels. The tire's static friction with any given patch of road does not change whether the car is two wheel drive or four wheel drive, meaning that oversteering due to anything other than excessive engine power does not change whether the car is two or four wheel drive.
If you have a car with 50/50 AWD, the force on the tires are distributed 25% on each of the 4 wheels, when a 50/50 AWD is driving in a straight line. With a FWD or a RWD, the forces on the tires are ditributed over only two wheels.
With "forces" I mean the force applied from the engine power.
When a car oversteers, the sideway there are also sideway force on the rear tires. As I said, the speed of a WRX in a corner is higher without losing grip than with a FWD/RWS. In that case, because the speed is higher, the forces are higher and you will exceed the sideway forces a tire can handle faster than you think. Don't forget that in my previous posts, I mentioned shifting the weight of the car onto the front tires, which makes the rear tires lose grip even faster. So, you can definitely oversteer a WRX easily, as long as the speed is high enough (that was my argument in previous post ==> showing off to friend etc.... ).
Let's take one wheel of the front suspension for instance. Driving straight forward, there is only one force on the tire. A force in a straight line. If you turn a secondary sideway force is applied to the tire. If the sideway force exceeds the straight forward force and the tire isn't designed to cope with this sideway force, this tire will lose grip and you have understeer.
If the forces are applied 25% on each wheel, it takes longer for the forces to exceed the forces a tire can handle thus making a 50/50 4WD more grippy than a FWD or RWD with all the engine power on only two tires instead of 4 tires.
A RWD or a FWD has the engine power divided over only two wheels making the forces on these two tires exceed faster (because there is more engine power on one tire compared to a 4WD) than with a 4WD. If the FWD and RWD has the same tires as the 4WD, the FWD and the RWD will lose grip faster than the 4WD making a 4WD better to handle and making a WRX more dangerous to drive because you ca go much faster through corners. Showing off to your friends with a WRX is catastrophic.
The above example is theoretical and not entirely correct because I didn't mention the mechanics of a differential, the suspension in general etc... .
I don't know anything about the mechanic's and electronic's of a car.
It is difficult to explain in English. It much easier in Dutch though.
It all makes perfectly sense in my head but putting it in writing (in English) is difficult and my sound strange of faulty.
I hope I make sense though.
How to correct understeer?
*
Decrease speed, forces on the front tires diminishes and the weight of the car shifts forward, creating more grip on the front tires. You can also apply the brakes
slightly to transfer more weight to the front of the car.
*
Open your steering. I.e. do the opposite of what you intuition says and instead of turning more, turn less thus decreasing the sideway forces on the front wheels, creating more grip on the front wheels
*
Apply the clutch to cut off the engine power to the front tires and the tires get more grip because the forces (other forces than engine power) is less and divided
almost equally over the 4 wheels. Use the clutch to push yourself into the driver's seat leaving your arms and hands free and have all the freedom to control the car.
*
Look where you have to drive to. Your hands (brain) will follow where you look at.
* As a very last resort,
use the e-brake. Only use this if you are going straight to a ravine on a road in Austria with snow on it and you're driving on summer tires. (Real experience I had and I managed not to go into the ravine
) I was trying to follow an Austrian 4WD VW Van with winter tires and I had a VW Golf II Manhatten on summer tires.
All the above didn't work because I was going too fast and wasn't able to slow down enough in time so I used my e-brake to alter my trajectory (turn the car away from the ravine). And summer tire on a snowy road in Austria is
Losing grip= when the speed (forces) of the tires exceeds the speed of the car compared to the surface the car is driving on. ==> Locking wheels = no speed of the wheels but the car is still driving. Spin the wheels on acceleration = speed of the wheels is higher than the speed of the car.
This is a simplistic explanation of what losing grip is.
Edit: All the car journalists, homeforsummer, Famine, niky, specially Scaff and other members on GTP, if I'm wrong, feel free to burst my bubble and correct me. Do it in a nice manner and don't hurt my feelings or I'm forced to start insulting people and get banned.
/justkidding