Ok, let's be specific here and try to keep it simple. Note I'm replying in this thread only just to keep things centred somewhat.
1. Why does the modder set a number for the torque? I thought all this stuff was calculated dynamically and "truly" from the physics engine (all sorts of complex calculations regarding suspension geometry, tyre forces, aero, etc.)?
Second sentence is absolutely correct. Don't doubt yourself there. There's a whole dynamic virtual world interacting with virtual tyres and wheels and suspension and steering geometry to produce dynamic forces at the virtual steering wheel. You can't fudge any of that as a modder.
But the game has to know how much steering wheel column torque is 100% FFB output. Maybe it could do some calculations based on the car parameters to work out a maximum torque figure and it would be close enough, but instead it's a figure the modder can set. This is probably a fair method because the modder knows more about how the car will be used than the game can guess at (a super speedway configuration of the DW12, for example, you could expect to encounter higher forces than the road course configuration; the game can't really know the difference [and the fact it doesn't is why the current single max nominal torque is leading to even lower forces in the road course version. A later update will have different values for the different configs, somewhat alleviating the problem]).
So something has to decide how much steering column torque is 'full force', and that's the modder's job. Design choice. Done.
2. i'm trying to determine how the car's "true" (as in no scaling or anything) FFB power, my real life wheel's power, and the game's STC all affect each-other...
The default STC is very low, so let's start there. Basically every car made will have a nominal max torque higher than STC, so the game scales all virtual steering column torque (0 -> nominal max) to your wheel at (0 -> 100%).
Example: The skip barber has a nominal max torque of 9.5Nm. Let's say at 3 different points around a track the steering column is currently experiencing (due to all the physics calculations) torque of:
4.25, 9.5, 13.75 at those points.
Since 9.5 is the 'full output' point, the game will attempt to send FFB to your wheel at: 50%, 100%, 150%. Of course you can't send more than 100%, so it's
50%, 100%, 100%.
If your wheel can produce 5Nm, you feel
2.5, 5.0, 5.0
If your wheel can produce 25Nm, you feel
12.5, 25.0, 25.0
Note that the powerful wheel is producing 12.5Nm when the virtual steering column is experiencing torque of only 4.25Nm. This is why it's a good idea to not ignore these figures and set the STC if you have a powerful wheel...
2a) How does the FFB scaling work if the car's true FFB can, let's say, hit 20 Nm, but my real wheel is only capable of 15 Nm, and my STC is set to 10 Nm?
Just like above, even though you've set a higher STC of 10Nm the game can see that the car has a nominal max of 20Nm, so it scales it just like before. When the virtual car is producing 20Nm the game says that's full force, so it sends 100% to your wheel which produces its 15Nm. Everything lower is scaled down, anything higher is lost (clipped).
2b). What about if we were to switch the real wheel and STC figures around in the example above (real wheel capable of 10 Nm, STC set to 15 Nm [same 20 Nm car])?
The car's max is still higher than your STC, so the game scales (0 -> 20Nm) in the car to (0 -> 100%) at your wheel. Car at 20Nm is sent to your wheel as 100% which produces its 10Nm. Lower forces are scaled, higher are clipped.
Switch those figures around again: car produces 10Nm, wheel does 15Nm, and STC = 20Nm
Now the game thinks your wheel can do 20Nm, so a car producing 10Nm will be simulated properly if it sends 50% FFB to your wheel; that would result in 10Nm at your 20Nm wheel. But because your wheel is actually only capable of 15Nm, sending it 50% FFB results in you feeling 7.5Nm. Setting STC higher than your wheel is giving you lower than real forces.
Finally, let's do it properly: car produces 10Nm, wheel does 15Nm, you set STC = 15Nm
Game thinks/knows your wheel can do 15Nm, so a car producing 10Nm will make the game send 66% FFB to your wheel, and you feel 10Nm. You feel the correct forces as calculated inside the game, and because your wheel can still produce more force you'll avoid nearly all clipping because your wheel can take up to 15Nm of simulated force before running out of room - which should be rare for a car set at 10Nm.
You can see in those last two examples that STC can help avoid clipping, but setting it higher than your wheel is capable of makes all forces weaker than they should be. It's much better to set STC correctly and use the FFB Mult if you want to reduce clipping in a specific car, so that only that car is made weaker.
If this scenario, there are two ways to fix it. The smartest way in my opinion would be to correctly set the STC to what your wheel can do. So raising it from 10Nm to 15Nm. However a 20Nm virtual steering wheel torque will still be clipped because it is above the STC value of 15Nm.
If the car is given a nominal max torque of 20Nm, the game scales that to your wheel. So you don't get clipping until the virtual steering column exceeds 20Nm. Remember we all have a default STC of 2.5; if the game just blindly used that we'd all be clipping nearly the whole time.
Adrian: you might want to reconsider your ignoring of these figures
