Perhaps this will help (from an old nogrip thread):
"2. AIW File
One of the most neglected aspects by the modders groups. If your track has a defective AIW file, you can either fix it (if you really like the track) or leave it alone only for online races. If you decide to go into it, then you'll play around with these values (if your AIW file doesn't have those lines, insert it manually!)
slowwhenpushed=0 // Insert it! Most tracks don't have this line and it cures the stupid AI slowdown when you're pressing them.
AIDraftStickiness=(3.0000) // Insert it! Ai cars stay on the draft for more long and it helps one to overtake the another.
AIRange=(1.0000) // The software core will calculate the AI performance based in two parameters: the *.RCD ability (see below about RCD file) plus the AI Range. 90% of their speed is based on RCD file, the remaining 10% is from the AI Range. If AIRange=1, the difference between the driver will me maxed to 100% of RCD values. It helps to avoid the bunch up races and gives more value to each driver ability. If you set this number too low (0.1, for example), the drivers will drive almost all the same.
AISpec=(0.0000,0.0000,0.0000,0.0400) //Insert it! This value theorically wouldn't work in GTR2 (it came with 1.255 version of Rfactor) but from my experience, it seems to work. It's for fine tuning and works in percentage (0-1), basically for AI slowing down. If you're experience unrealistic AI acceleration, increase the first value, if they're are too fast in straights, increase the second, if they're cornering too fast (seldon to see), increase the third and finally increase the last one if they're breaking unrealistically close to the apex. In this case, I've raised the last value to 4% and it helps to avoid rear-end AIs.
3. *.HDC File
There's a number of tweaks which can be made in the physics vehicle file. They are:
AIMinPassesPerTick=0 // The default values are too low (e.g. =2) so you must increase to 6, 7 or even 10. If you want the AI cars being simulated in real time, set it to zero, but anything above 6 will produce a more realistic AI physics simulation. However, this will demand more CPU, so if you don't bare a good i5 or i7 is better to be careful and avoid 10 or zero values.
FeelerFlags=15 // This will create the most possible accurate collision detection system, but you'll need to use the collision feelers. This part would be optional, since you'll need 3DSimed to get the real car dimensions for each competitor. But, if you willing too, it's a worth effort.
First, delete the "//" (comment marker) from the collision feelers lines and remove the line "FellerFlags=X" from the top of it, since it's already informed at the beginning of HDC file.
Now, you need to know the coordinate system is strange (at least for me):
+x = left
+y = up
+z = rear
Second, you'll notice there's a bug in most of cars I've seen so far which is the wrong signal for FeelerTopFrontLeft, FeelerTopFrontRight, FeelerTopRearLeft and FeelerTopRearRight. The lines below are already fixed, so pay attention on it. Left is always positive and right is always minus!
//FeelerFlags=15 // or remove this second instance or simply leave the "//" infront
FeelerOffset=(0.0, 0.0, 0.0) // leave it alone, it won't be used.
FeelersAtCGHeight=0 // Set it to zero. You'll provide all real corners coordinates for the car.
FeelerFrontLeft=(1.003,0.384,-2.554) //front-left corner collision feeler
FeelerFrontRight=(-1.003,0.384,-2.554) // front-right corner collision feeler
FeelerRearLeft=(1.003,0.384,2.586) //rear-left corner collision feeler
FeelerRearRight=(-1.003,0.384,2.586) // rear-right corner collision feeler
FeelerFront=(0.064,0.384,-2.639) // front side collision feeler
FeelerRear=(0.064,0.384,2.587) // rear side collision feeler
FeelerRight=(-1.039,0.384,-0.247) // right side collision feeler
FeelerLeft=(1.039,0.384,-0.247) // left side collision feeler
FeelerTopFrontLeft=(0.478,1.540,-0.298) // top front-left collision feeler
FeelerTopFrontRight=(-0.478,1.540,-0.298) // top front-right collision feeler
FeelerTopRearLeft=(0.652,1.511,2.323) // top rear-left collision feeler
FeelerTopRearRight=(-0.652,1.511,2.323) // top rear-right collision feeler
FeelerBottom=(0.064,0.249,-0.247) // bottom feeler
To know the real car dimensions, you'll have to open it in 3Dsimed. Take note of dimensions, subtract 10 cm from each one (helps to prevent the AI to AI crash without significant visual glitches), change the values above (double checking the signals + and -) and remember to leave the rear-wing out of the box - it's not nice to see the car turning over based in the rear-wing position, it's preferable to leave the wing going through the tarmac than the strange "rigid rear-wing" effect when turning over.
If you have patience enough, the amount of AI to AI crashes and the physics reaction will improve a lot by following this procedure. If you don't use feelers, the game will create a automatic box around the car which could be pretty rough for calculations.
RearBrakeSetting=36 // some modders make a little confusion here and put improper values to this variable, causing oversteering in AI cars and causing havoc on some tracks. Example: Daytona Road Course, where the first corner is after a really hard braking zone where the wheels are still steering. Using the value = 36 (or so) you'll have a AI brake distribution (64:36) which can be very bad for human drivers, but it's good for AI. I often see values as 60 or 55 here, and it means a brake distribution (40:60) or (45:55) which is way wrong and induces demolition derby due a lot of spinning. Remember when you adjust this value the default setup car will be 64:36 (in this case) so, you should change it before drive your car (or on the fly).
BrakePressureRange=(0.00, 0.01, 101)
BrakePressureSetting=100
I caught this values from AI Reborn and it seems to help a lot on preventing AI to AI crashes. Theoretically it shouldn't be like this since the default value is 80 + 20 = 100 % of pressuring but for some reason it doesn't. So, I advice to use those lines in HDC files.
ABS4Wheel=1
ABSGrip=(1.05, 0.25)
Those lines give more brake effectiveness for AI. Default are 1.00, 0.20 but I found with those values there's less AI rear ending during the races.
AITorqueStab=(0.95, 0.95, 0.95) // This is a very known tweak (thanks Dutch Devil) which works only when there's a contact between 2 AIs or human car versus AI. Most of you probably noticed that AI cars is rock-stable and closely to impossible to make them spin out. By reducing this values down to 0.95 make they obey the physical laws, so when they crashes onto you (or vice-versa), they have not magical stabilization anymore. Working along the AITorqueStab we have more variables as AIEvenSuspension, AISpringRate, AIDamperSlow, AIDamperFast and AIDownforceZArm. I'll not take too much time on those, they're pretty well covered by DutchDevil tutorial (pinned thread of this forum).
AIDownforceBias=1.0
This is a percentage between the AI setup downforce (0.0) and scripted downforce calculated by the game (1.0). If you're not using AI specific Setups, you should use 1.0. In certain sort of tracks as Le Mans with very long straights, to have a good AI Setup might be the way to go (more details further). But if you're lazy to make a setup for each car, you'll rather set this value = 1.0 and let the computer calculates the correct downforce. But it will not give proper gear ratios to AI."
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AI Min Radius is tricky, from what I can tell it controls the distance at which tehy are aware of other vehicles; set too low and the AI is like NASCARE - constantly "trading paint", but set too high and they are too busy staying out of each others' way to race effectively.
And again I recommend reading Von Dutch' AI Tutorial and Barry's GTR2 Reborn, both have extensive information on adjusting the AI.
