WARNING: Long post ahead. If you are not concerned with FFB discussion on a technical level you should probably just scroll down
In which case they are using some very misleading descriptions indeed.
Self Aligning Torque is a tyre generated force, its the force generated as a tyre turns (and creates slip) as the rubber attempts to 'get back' to its original position. Effectively torque is generated as the rubber resists being twisted as slip is generated, which is felt as resistance to steering input. So as you turn the tyre resists and you feel 'weight' in the steering, however the rubber will reach a point at which it can no longer twist (as it starts to lose grip) and the force will reduce and weight will be reduced. While it can be influenced by the suspension geometry (caster in particular), its not a force generated by the steering rack, simply transmitted from the tyre via the rack.
Tyre Slip is not strictly a force, but rather the difference (in cornering) between the direction the tyre is travelling and the direction it wants to travel. Tyre Slip does produce a force (Self Aligning Torque), but is the cause, rather than the name of the force.
Its also something that will vary in terms of how abruptly it will break away, and while it will not normally breakaway as quickly as it builds it is still generally very abrupt and having experienced it countless times is not what I would describe as subtle. Particularly as you have been countering the build up in torque to that point.
Source:
http://www.engr.colostate.edu/pts/Job/Understanding Parameters Influencing Tire Modeling.pdf
Source:
http://white-smoke.wikifoundry.com/page/Self+aligning+torque+and+the+Gough+plot
Edited to add:
You can see both slip and SAT is action for yourself with a very simple experiment. Get a pencil eraser (rubber to all of us non-Americans) and put it flat on a surface (this is your tyres contact patch), then push down on it with you fingers (to provide load) and slowly try and twist it on the desk as if it were a tyre turning. You will feel the resistance build (this is Self Aligning torque) and see the eraser change shape as the direction it wants to be in and the direction you want it to be in differ (this deformation is in some ways the tyre slip). However as you keep turning you will notice that its will eventually lose this battle and all the torque that has been building will disappear (and quite rapidly). What is happening to the eraser in this is exactly what is happening to the contact patch of your tyre as you turn and forces build.
Oh you will also notice that the more force you apply to the eraser the harder it is to initially turn, but the more rotational force it will sustain before 'letting go', which is showing how your maximum tractive force is a result of load (the pressure you push down on the eraser with) multiplied by the mu of the eraser (how sticky the rubber it is made of is). This is again exactly the same with tyres, the total grip you get is a result of how sticky the tyre compound is multiplied by the load placed upon it (it does get more complicated that this as this is not a linear increase, unless you are applying that load via down-force).
Thanks for the really informative post 👍 It's gonna take me a while to read that pdf, but I read the webpage and it does make sense. Love that eraser analogy too.
I don't have an engineering background, so it everything I've learnt is just by seat of the pants feel (or seat of the fingers in terms of sims
). I have no doubt what you are saying is 100% correct when applied to real life, and all sims are also trying to get to that point. So I won't contest what you've written here.
For my original post however, I was merely remarking on how FFB settings seem to be implemented in sims (which may or may not be correctly named, and I'm just going by what the actual settings screen says here).
For
AC, you have this screen below. Gain is the master setting, and to me seems to combine SAT and steering rack forces. Slip effects is canned vibrations when the rear wheels lose traction. Enhanced understeer effect is the light feeling you get when understeering. Without this box ticked the wheels doesn't get light all that much when understeering. The devs themselves have said this is an artificial setting, so you can see where I get the impression of understeer effects only being "subtle".
For
GSCE which uses rFactor's physics + RealFeel, the settings look like this (you have to edit it manually in notepad):
MaxForceAtSteeringRack=1700.000000 (steering rack + SAT)
SteeringDamper=11500.000000 (artificial to add resistance)
FFBMixerRealFeelPercent=100.000000 (how much of the FFB is from rFactor's base FFB or RealFeel, in this case it's 100% RealFeel)
FrontGripEffect=0.200000 (gives light feeling when understeering, the higher number, the more it's exaggerated)
SmoothingLevel=0 (how much the FFB is filtered)
Kf=11500.000000 (this and 3 below settings only serve to make the wheel heavy when turning it at a standstill - aka "Parking Lot Effects" - because rFactor tyre physics goes awry at low speeds)
Ks=5.000000
A=1.500000
Kr=4.500000
For
GTR2, it uses base rFactor physics. Again, you have to tinker with notepad here. I only put the parameters which are not canned effects. Bolded settings are the main ones. Steer force is steering rack + SAT. Grip weight is the light feeling when understeer (the way the FFB is mixed in the game you momentarily lose steering force when the wheel goes light - that's why I set mine to zero). Grip factor is proportion of FFB derived from front wheel (realistically, 100% from front tyres).
FFB Gain="1.00000" // Strength of Force Feedback effects. Range 0.0 to 1.0.
FFB steer force average weight="0.90000" // How much weight is given to new steering force calculations each frame (0.01 - 1.0). Lower values will smooth out the steering force, but will also add latency.
FFB steer force exponent="1.00000" // Steering force output "sensitivity". Range 0.0 to infinity. 0.0 to 1.0 = higher sensitivity, greater than 1.0 = lower sensitivity.
FFB steer force input max="-11500.00000" // Recommended: 11500 (-11500 if controller pulls in the wrong direction).
FFB steer force output max="2.00000" // Maximum force output of steering force, recommendation 0.8 to 2.0
FFB steer force grip weight="0.00000" // Range 0.0 to 1.0, recommended: 0.4 to 0.9. How much weight is given to tire grip when calculating steering force.
FFB steer force grip factor="1.00000" // Range 0.0 to 1.0, recommended: 0.2 to 0.6. How much of a factor the front wheel grip is on the steering weight.
FFB steer update thresh="0.00000" // Amount of change required to update steer force/vibe (0.0 - 1.0). Lower values = steering force updated more frequently = lower frame rate.
FFB steer friction coefficient="0.00000" // Coefficient to use for steering friction. Range: -1.0 to 1.0
FFB steer friction saturation="1.00000" // Saturation value to use for steering friction. Range: 0 - 1.0
FFB steer damper coefficient="0.00000" // Coefficient to use for steering damper. Range: -1.0 to 1.0
FFB steer damper saturation="1.00000" // Saturation value to use for steering damper. Range: 0 - 1.0
LFS is non-moddable so there's no way to see the inner workings of the game. In game settings only shows Gain setting which is a master control. Again you can't really feel the wheel lightening much when understeering.
For
Dirt Rally, Codies gives the following explanations (source:
http://blog.codemasters.com/dirt/06/dirt-rally-force-feedback-update/). My thoughts are in square brackets.
- Self Aligning Torque – scales the strength of the steering forces. [SAT + steer rack combined?]
- Wheel Friction – scales the static friction of the wheel. [sounds to me like parking lot effects]
- Tyre Friction – scales the dynamic friction of the tyre (this is friction when the tyre is in motion). [probably the light understeer setting]
- Suspension – scales the information from the road’s surface via the suspension. The harder the impact to the suspension the greater the force felt.
- Tyre Slip – scales the vibration felt when the rear wheels slip (front wheels are covered by the steering forces). [what I thought was understeer, but it's oversteer, whoops. Also, this means SAT above = SAT + steer rack + front tyre slip?]
- Collision – scales the strength of impacts to the rigid body
- Soft Lock – scales the strength of the soft lock effect, the higher the value the stronger the soft lock force.
TLDR: While I agree with you that steering rack, SAT and tyre slip are all different forces in real life, most sims treat (SAT+steer rack) as one setting, and tyre slip as another. In my original post I was just suggesting to
@JvM that the reason why hillclimb cars go (too) light when understeering is possibly due to tyre slip setting being too high and he should lower that (not SAT as someone suggested). Though after reading the Codies' explanation above, probably he should try lowering tyre friction instead (sorry JvM!).
No it's called overmoaning. I've read here of people skipping the game due to ffb issues. Yesterday someone posted "non existent" ffb. This is not constructive and doesn't help people that are waiting to judge the game.
I agree that skipping the game completely just because of FFB is too much. It's really not bad and it has been improved from what was in Early Access. Just that tarmac physics has always been an issue with Codemasters and now that they have a PROPER sim in the form of Dirt Rally, some of us who are OCD about physics/FFB want to see them get it just a littttle more perfect.
No one will ever reach perfection, but it doesn't hurt to aim for it y'know?
Of course if you are happy to just treat it as a game, then by all means do 👍