In the 'Advanced' course, we will take another step forward in our learning. Participants will continue refining what they have learned in the previous courses and expand on it using the dampers, differential, and aerodynamics.

NOTES;
- Check in at the schedule time, do not be late please.
- A short discussion period will be followed by 10 minutes of track time at which time all participants will discuss the track time with the Mentors.
- The course will be broken into 4 to 5 smaller segments, as mentioned above, each focusing on specific items.
- The HPDT session will run from roughly 60 minutes in length. Following the course, participants are welcome to run a short race if they wish.

R2P Setup Development Articles
Dampers
Diff

I'm a little concerned with the Differential discussion beginning where you state, "When you begin to lose traction with a loose power-diff settings, all drive power is redirected to the wheel that has lost grip, usually the inside wheel)."

It looks like...especially with the misplaced closing parenthesis...this thought has not been well fleshed out yet. My understading is:

Solid axle: Both wheels are locked so that there is a moment (angular force) applied to both wheels equally. When one wheel (usually the inside wheel) loses traction the amount of resultant force (Newton's equal and opposite) on that wheel is reduced and the amount of resultant force required from the other wheel increases. This increased resultant force is the problem with solid axles in that it is more likely to increase beyond the dynamic friction of the tire and result in complete loss of traction.

Fully Independent axle: Both wheels are free to turn so that the moment present in the drive shaft will be distributed to the wheel which has the least resistance. So, as you say...when one wheel loses traction then the power will bleed out through that one wheel and result in a loss of power to the wheel that has traction.

Limited Slip (PosiTrac) axle: A mechanism (in my corvette it is a pack of clutch disks on each side of the half-shafts) causes the difference between the speeds of the wheels to shift the moment in the drive shaft to the wheel that has the most resistance. So, with this setup, when the inside wheel starts to lose traction...as with a solid axle...the outside wheel gets more force put on it. But, the benefit is that with a limited slip differential, if the outside tire begins to lose traction then the power will shift back to the inside tire. This results in more overall grip and more consistent traction control.

So, my understanding is that a racing differential is all about adjusting how the moment is transferred when one wheel loses traction...in my covette it is the amount of slippage in the clutch packs. The number and type of clutch disks determine how much of the moment is transferred to the other wheel when one wheel loses traction, and the springs which hold these packs in place determine how fast the transfer takes place.

But, the discussion on differentials sounds like some sort of virtual differential which can have a sliding scale between a free floating rear end and a solid axle. Sorry, but I just don't get it. Is a modern racing differential some sort of morph between a floating diff. and solid diff.? I'm sure it's more complicated than my 1975 spring loaded clutch pack, but I just don't see what's going on...my limited understanding of my own differential is clouding my thinking.

As applied to my differential the preload is the amount of pressure on the disks at rest...accomplished with shims. The amount of moment transfer is adjusted with type and number of clutch disks. And, the variance between power and coast adjusted with directional friction nodes on the clutch disks so that they have more friction in one direction than the other. But, I'm not entirely sure how the simulation handles it, so this will be a very important session for me...to have a guided "feel" for how these settings effect the handling of the car in a way that is independent of the underlying details.

A nice explanation Steve. Took me a few read-through before I began to grasp what you were saying.

I do not get any sense of feeling that GTR/rFactor models a LSD [properly?]. I do not know accuracy, but how you explained an LSD is not how the diff's in our simulations work. They are like your definition of an independent axle.

They seem like an LSD to me.

for a rear-wheel drive car...

A low number (percentage) for the POWER setting results in less slipping before the diff locks. This leads to a great deal of power-on oversteer. Increasing the number for the POWER setting allows for more slip but at the expensive of acceleration and turning performance under power (understeer).

Same for the COAST setting. A low percentage means not much slip before the diff locks which leads to a good amount of power-off oversteer at turn-in. Especially with a low ENGINE BRAKE MAP setting which allows the throttle to close more, giving more engine braking. Increasing the COAST percentage allows for more slip under engine braking and less chance of loosing the rear but with less desired turn-in.

The diff settings are among the most important in my book.

In fact the FIA GT reglement says that electronic, pneumatic and hydraulic diffs (sensors in it) are forbidden. Even a system with viscous-clutches is forbidden. Its a simple mechanical limited diff (LSD) what is being used, without any control of torque or wheel-rpms. I would say they use LSD with mechanical preloaded clutches (although they wear out till high powers and long usage) because its simple to set the amount of slipage.

My understanding of this subject:
Setting up the diff means in short:
The higher the settings, the more UNDERSTEERING you ll get.
Theoretically you want a 100/100 diff to get all power on accel. and on braking, this causes heavy understeer and you cant go early on full throttle out of corner. On the other hand you want a low diff, to achieve max turning and to go on full throttle as early as possible, but in the entry the car is fragile on the rear and at exit the power goes into slipage and disappears into hot air.
Finding a compromise means here to set the amount of UNDERSTEERING that is comfortable AND fast.

That was my general understanding too Roman, until I was proven wrong by the sims. You can get more understeer from a very low diff or a massive oversteer from higher diff settings. It baffled me so I started figuring out how our sims are doing the diff...

"You can get more understeer from a very low diff"
I never did this experience. In what situations?

Yes, in rare situations there can be a oversteer with very high diff if both wheels lose suddenly traction by agressively hitting full throttle. Best to see on wet tracks.

The Power and Coast setting lock the diff tighter for higher numbers. ONLY in the direction of that name.
You are effectively controlling 'clutches' (but will be done via mechanic/hydraulic systems most likely really) for just that power direction.

The Preload setting tightens for both directions, but it is tighter for a lower number.

That seems to be the case in most Mods, but it really is up to the physics file and if it was set up for values of that direction or not. They could be done inversely for any Mod if the maker did the numbers that way.

ISI sims look like they always replicate a Formula 1 diff. Not an LSD etc. So it is a more complex system than a simplistic LSD.
Some Mods blank out certain adjustments, to try to remove your ability to set up using those extensive abilities, but in reality the Diff is always still operating as the fully 'programmable' one. You just don't get to change the values. And if they do it all right they can make it mimic an LSD close enough.

The problem is ever knowing if they did the actual physics file stuff 'right' - for any, or all, of those cases off total adjustment, or limited adjustments and ranges.
So you pretty well need to drive any Mod and test it for responses to ever be sure.

As with all setup things, you most often need to compromise on the Diff. A looser Power setting will allow better turning, and less understeer. But often you can use higher Power setting to actually turn better - because you slip the rear (slide) for better car rotation. You drive 'different' to get the actual car response you want.
So even though one way is technically more correct, the other way can achieve a better result - all depending on the corner area, and what other track areas there are which suit the grand total of your Diff strategy best.

That applies to pretty well all setup aspects.
Using shocks to alter the "turn-in understeer" can be a totally useless, and even detrimental, thing if other aspects of the track made it more useful to have them giving more useful responses for others aspects of the car in those other areas instead.

That is why setups are a 'black art'. There is no hard and fast rule ever. Only a grand total of what a specific track and the best way to drive it gives.

Example:

You might want a looser Diff Power setting for one hairpin area to be optimised. Some setting allows a good 'high' use of power input, without pushing you wide with oversteer. But it messes up 5 other corners where a tighter Diff is more useful. So you can find it is better to run the tighter Diff but alter your turn-in strategy, and power usage, to get the hairpin as good as the looser Diff could anyway.
You just need the different driving input strategy.
Turn-in probably where you were before anyway, but harsher by a bit. This will keep the nose tracking the inner curb once some more power applied tries to push it wide (so you are effectively predicting understeer and compensating in advance for it), and it will also give more lateral load to the rear which will make it slip out. All inputs just by that correct amount for the task. A combination of power input, and correct steering as required, will keep the car negotiating the turn optimally. You are not 'tracking' the turn and 'driving around it' like the looser Diff would, you are 'slipping' the rear end around it, but you are now still doing the same effective total racing line anyway.

The tighter diff will even allow better high power application once you straighten up more - which is achieved nice and early by allowing rear rotation (slip) to get the car more 'exit straight aligned' before the turn is even fully completed. You were doing the whole turn with slight rear slip anyway, and in preparation for the straight-lining launch you will have reduced steering to straight ahead before you are even in-line for the straight exit - because the rear slip is going to complete that last portion for you anyway. Thus you are steered straight and ready to go into high power already before fully out of the turn.

Someone driving 'around' the hairpin, on a loower diff, can power on a BIT sooner, but not with more power anyway really. And they also cannot increase the power levels as fast as a tighter diff can once it is staight. The loose diff will need it fed in more gradually, initially to prevent spinning up the lighter loaded inner wheel but which can even break traction of a car that is straight-lined already (which the loose Diff is going to allow to happen much easier than the tighter Diff needs to worry about).

So come the final result of the whole sequence - and off down the straight to top speeds - and the tighter Diff can have won the race for that area. Or at worst be equal anyway.

Setting the Diff for the absolute optimal ability of either of those strategies is essential for that strategy to do its best. But remember, you quite likely did this so that other track areas were not messed up! So if you had chosen the looser Diff way (and somewhat more of a technically right way to drive a car), your whole lap time would have suffered.

In ISI sims it is rare that tires matter too much. They cope with excessive abuse just fine usually. So that means using slip, and spinning up wheels here and there, is most often of no detriment really.
Even some real car classes it isn't important. Short races for a class etc. So even a real car can benefit from various 'turning' strategies, to suit what gives the truly best lap time. And in most cases they would not be using 'totally true tracking' tires anyway.