Any car-physics experts around?

I`m trying to make a league out of the many great musclecars that has been made lately but I find it a bit hard to make them compatible.

I do not know too much about how to modify the car-physics, all I can do is to uppgrade tyres, put in some equally tuned race-enegines, change gear-settings and (try to) adjust the carweight a bit closer to the real thing. Btw; some of the cars has wery strange weight-numbers in hdc & sp-files; shouldn`t these files correspond/show the same weight-values?

Now if there only was a car-physics tool to make all these numbers understandable.


Dyno 2003 is a good tool to make realistic enegine-files, free downoad here:

http://loco4fomoco.com/video.html

- just search up and add the needed head-flow and cam-files

To follow up this; here`s one example of strange physics on big US-cars:

HDC-file:

Mass=1493.0 // all mass except fuel (1283kg car + 75kg driver weight)
Inertia=(2180.25,2443.82,426.88) // all inertia except fuel

Still the same car, now SP-file:

[BODY]
name=body mass=(1142.0) inertia=(1081.0,1210.0,177.0)
pos=(0.0,0.00,0.0) ori=(0.0,0.0,0.0)

Shouldn`t these files correspond?

Another car, same class:

HDC-file:

Mass=1565
Inertia=(1190.933,1558.327,367.543)

SP-file:

[BODY]
name=body mass=(1090.0) inertia=(1239.0,1387.0,170.0)
pos=(0.0,0.00,0.0) ori=(0.0,0.0,0.0)

And so on.

Since I have no references I`ve just putted in some deacent numbers to equal out a bit, like this:

HDC-file:

Mass=1540
Inertia=(1540.0,1560.0,360.0)


SP-file:

[BODY]
name=body mass=(1540.0) inertia=(1540.0,1560.0,360.0)
pos=(0.0,0.00,0.0) ori=(0.0,0.0,0.0)

Mybe a bit heavy for a car in race trim but at least corresponding values.

Hi unfairlane,

the values you mention look a bit like NFS??

the mass is as you stated the static weight of the car - e.g. the SCCA cars should have around 1100-1200 kgs w/o fuel or other liquids nor driver - which makes a total mass of around 1180-1300 kgs - the value needed in the .hdc

the inertia is calculated by means of a complex integrale formula with torque, mass, speed of objects and some more issues. For the sim cars I normally use experimental values - calcuted by rule of thumb. So for let´s say the Mustang I´d use with 1180 kg weight 1160 N in x-axis, 1400 N in y-axis and 300 N in z-axis. The Center of gravity will be due to a live axle at +260 mm from ground. You need to experiment a bit with because it corresponds with the tire grip levels and torsion values and the aerodynamic forces. The higher the aero forces, the higher the possible inertia can grow. Since the inertia is a dynamic force, the static values in the .hdc may not be as close to reality as we experience it while driving a real (race)car.

The values in the .sp file are valid only for a specific part of the car, the complete body or any hinges, wheels and so on. Thus the values are different from the .hdc

Maybe this will help you in finding the desired values

Cheers streckensau

Don't want to start another thread, so I'm posting my question here: does anybody know which are the BRAKES LINES/PARAMETERS in GTL?!

I'd like to reduce the brakes efficiency for the cars from the 50s, but can't figure out what's the line or lines I need to modify. For example, when braking from 100 km/h, if it takes 40meters of space now, I want to make it 50 meters. Also, the parameters are in the HDC file or some other file OR both?! Any help is welcomed, thanks!

In the HDC-File, each corner of the car (suspension obviously) has a line 'BrakeTorque='. You might lower that value as a first measure. You might also want to carefully play a bit around with the grip values of the tires, because if you just adjust the brake torque, you might never get to the point the wheels lock up. On the other hand, if you adjust tire grip without brake torque, you might end up with the wheels locking up immediately if you touch the brakes. Also, if your car is running on drum brakes, you might want to raise the 'BrakeDiscInertia'-value

Though that's just part of the truth, brakes in the '50s were less about the absolut torque the brakes could deliver, but heat buildup and dissipation as well as brake wear. Fresh, cold drum brakes were always able to lock up all four wheels when needed, but the fascinating stuff is to know the guys mostly used engine braking and scrubbing of speed via the tires by going sideways, to save their stoppers. Using the brakes to much would quickly make them fade away.
Reports on the exact circumstances of Pierre Maréchals fatal accident at Le Mans 1949 differ a bit, but they all agree in the fact the car had NO brakes due to a burst brake line. For several hours. And they were charging for a podium. Go figure

Hi MG without getting too complicated I adjust this line in HDC FILE

BrakePressureRange=(1.00, 0.050, 11) // brake pressure


BrakePressureRange=(0.80, 0.050, 11) // brake pressure (LONGER STOPPING DISTANCE LESS PEDAL POWER)
BrakePressureRange=(1.20, 0.050, 11) // brake pressure (SHORTER STOPPING DISTANCE MORE PEDAL POWER)

Adjust to your preference

OK, thanks a lot, guys. Really helpful.