Yesterday I was testing the new BMW Z4 GT3.
I know, that optimal slip angle for FIA GT cars is momewhere between 6 and 8 degrees.
I wanted to check if it is right in this game.
Here is the little explanation of the things I am describing.
On the left you see the "setup debug" application. You can enable it in this file (\Steam\SteamApps\common\assettocorsa\system\cfg\assetto_corsa.ini) by setting this: ENABLE_DEV_APPS=1
accG (acceleration measured in G) - these are the G-forces acting on the car. From the left: lateral G (when you turn), vertical G (measuring bumps), longitudinal G (braking, accelerating).
I will be focusing on the "lateral G" (most to the left value).
slipAngle 0 and slipAngle 1 - slip angles for front wheels, "slipAngle 0" is front right wheel, "slipAngle 1" is front left wheel.
Tyres have their own optimal slip angle (measured in degrees), at which they produce the highest grip. For GT tyres it is between 6 and 8 degrees.
BMW Z4, soft slick, optimal slip angle.
In the video above I am slightly increasing steering angle.
I noticed, that when "slipAngle 0" is reaching 7 degrees, we can see maximum of 1.75G of lateral force. Which is the highest in the whole test.
Also after exceeding 7 degrees of slip angle I can feel slight reduction of FFB force.
From these 2 things I can say, that 7 defrees is the optimal value of slip angle. Ok this is good.
After I slightly exceed 7 degrees (i have 8 degrees of slip angle at this moment) of slip angle i can see, that lateral G sligthly decreased to above 1,6G and a little while later to just around 1,5G.
BMW Z4, soft slick, maximum slip angle.
In the above video I wanted to see how much lateral force ("lateral G") can these tyres produce at higher slip angles.
I once again steer more and more, producing higher and higher values of lateral G, which tops at 1,75G, when front right tyre (slipAngle 0) has 7 degrees of slip angle . So it confirms what I saw in the first test. Good.
Later I increase steering to maximum lock (see steer value equals 320). The front right tyre's slip angle (slipAngle 0) is showing now 21.5 degrees (which is over 14 degrees more than optimal value).
During that time I can see, that lateral G can reach over 1,6G at the first moment, and later it drops to around 1.4G. Remember, this is when I have my steering wheel at full lock, with tyres exceeding optimal slip angle by over 14 degrees.
By comparing these 2 results, we can see, that the difference in lateral force between using just a little too much slip angle and way too much slip angle is minimal (just few %) and in my view too little.
After the peak of the curve, lateral force can fall off 30% within a few degrees of extra slip angle. At these high slip angles most of the contact patch is sliding, producing a lot of heat and wear.
Source:
http://insideracingtechnology.com/tirebkexerpt2.htm
This graph shows amount of lateral force lost after exceeding optimal slip angle.
When cornering, in order to drive fast and to use the tyres maximum traction, it is important to try to remain in this 8 – 10 degree slip region. Generally, sudden steering inputs (and indeed sudden use of throttle/brake as shall be explained later) cause the tyres to go beyond this region. It is therefore important to be smooth with all driver inputs in order to remain in this maximum traction zone.
Source:
http://www.macgracing.co.uk/trackdays_setup1.shtml
This quote is refering the tyres in real life (with a bit bigger optimal slip angle than in this BMW).
In Assetto Corsa it seems, that you don't have to be very smooth to be fast, because the tyres behaviour is too forigving past optimal slip angles.
For example you can drive like in video below and you won't loose as much time as you would if you drove like that in real life.
In my opinion with this tyre behaviour in this game, it promotes over agressive driving (when you drive aggresively, you use bigger slip angles).
I think, that you can often have better lap times, when driving aggresively, then when trying to be very smooth.
