Bread82, thanks for sharing the links.
I believe that in real life preload means the diff is
locked until a torque difference is achieved between the left and right wheels (
link,
link,
link,
link).
If I may throw in my own take on how diffs work in real life (please correct me if I'm wrong, also
here is a great page)
- An open diff (0 / 0 / 0 in GT5) sends torque down the "path of least resistance" (increased grip = more "resistance" for that wheel). If both wheels have enough grip, it's all cool, but when the one wheel starts to spin, its grip decreases so the open diff sends all the torque to that wheel. So the gripless wheel is spinning furiously and you end up going nowhere.
- A locked diff (60 / 0 / 0) means that both wheels must always travel the same speed. But as you go around a corner, the outside wheel needs to travel further (therefore faster) than the inside. So, instead, a tyre must skid so that you can turn- this often makes the car harder to turn.
- The best of both worlds is a diff which is locked when it needs to be (full throttle) and open the rest of the time. But then this can cause harsh handing effects, so we need to add a few more things and we end up with an LSD (which contains complicated things like lockup %, coasting lockup and preload)
- pre-load "smooths out" the LSD's behavior. By keeping some diff lock even when the diff is unloaded, it reduces nasty transitions as you go from throttle to brake. To understand how it works, imagine you need to change a flat tyre on your car: with an open diff, the wheel in the air will spin freely; with preload the wheel will not turn until you push it with enough force to "unlock" the diff. So while you're cornering, initially the diff will be locked, but once the difference in speeds (outside wheel needs to travel faster) causes enough torque difference across the axle, the diff unlocks and the car will turn as if it has an open diff (assuming you are not accelerating or braking).
As for the differences between real life and GT5, IMHO
- GT5 does not include the understeer caused by too much diff lock (when you have enough traction, the locked diff pushes the inside wheel faster than it needs to go, which causes understeer)
- it is not possible IRL for a mechanical LSD to spin the outside wheel faster than the inside. However, this happens in GT5, which is why the "GT5 super Diff" can drown out the effect of suspension settings.
Hope this helps.