# Community Forum

## wheelshape tire forces

Forum Overview >> Scripting

 Category Scripting Created 20.12.2016 12:03

Michel Dorge (Unknown) 20.12.2016 12:07
Hi,
I was wondering if there was a way to override the "computeWheelShapeTireForces" function ? (if this is the one that is called when computing the tire forces after engine props and differentials had been set)
Could you give us the current way of "computing tire forces" ? is it an exponential function ? I mean, how do you transform the stiffness + load into the final force delivered to the ground ?
Michel

*turbostar* (federicocuci) 09.05.2017 18:00

Emil Drefers (Unknown) 10.05.2017 06:54
Hi,

not sure what this function does in detail internally.
It could work as you suggested, but if you want to override that ... just choose a calculation/implementation of your choice :)

@Michel, if your question is still ongoing, I could ask our CTO to have a look.

Cheers,
Emil

Michel Dorge (Unknown) 10.05.2017 17:41
Hi,

by the moment, I am trying to add lateral forces by myself (function "addForce") to try reproducing something "real". I think I get something "good", but I need more time to fine tune it.
Meanwhile, it means there are as many forces as there are wheels to apply to the vehicle at each iteration (frame). I guess there are already others forces applied to the "poor" vehiicle" by the default game engine and so, I fear for the game stability with many vehicles moving at the same time (hired helpers or multiplayer game with heavy vehicles featuring many wheels)
I think this would be far more efficient to keep the default system to apply the friction forces, but I would need somehow an access to the function that compute the tire forces. (our main problem here is : in real world, on "soft" ground, the combination of lateral + longitudinal force far exceed what we can witness on "hard" terrain like asphalt. currently, the game engine is set up for asphalt, but we have no way to tune it for "soft terrain". If we put enough "friction/stiffness" for the lateral part of the forces, the longitudinal forces are far too great -> too much tractive power. If we set up the parameters to get a "proper" tractive power, the lateral friction suffers a lot.)

Another point that I witnessed several times while testing = the "still" lateral slip is set to 20° (0.35rad)
This is somehow good to get stability when driving in a straight line, but that also means we get far less lateral forces when cornering very gently (we can even lose control because there is no more lateral forces when the computed lateral slippage get too close to 0 => 0 lat slip = much forces, 0.1 lat slip = very very small amount of forces => ON/OFF effect)

regards,
michel