Tire jbeam values

Stribeck Exponent and Stribeck Vel Mult don't seem to do anything and they are not present on some newer tires, probably deprecated features. As for softness coef it makes the tires behave more like racing slicks.

 

In the node friction code we use a function called the Stribek curve to move smoothly from a sliding friction coefficient at rest, to an ultimate sliding friction coefficient, as a function of sliding speed. The shape of that curve is mainly determined by the stribekVelocity in the groundmodel, where the larger the number, the higher the sliding speed required to reach the sliding friction coefficient.

The node is able to modify the stribek curve shape using stribekExponent and stribekVelMult. The default stribekExponent is 1.75 and the default stribekVelMult is 1, so if you don't see them defined in the tire jbeam, they are using those defaults.

A higher stribekExponent will cause a more "S" shape decrease in friction.. so, the friction will stay near the static value for some amount of sliding speed, and then swoop down to the sliding friction value. A lower stribekExponent, will cause a more sudden decrease in friction right from rest, but then decrease more gradually from there. stribekVelMult just multiplies against stribekVelocity and contracts or extends the curve.

Playing with these values can make the tire more or less forgiving at the limit, but going too extreme can cause overall grip loss at high speeds (because the tire nodes slip much faster in absolute velocity for a given slip ratio or angle), or can make locked braking way too powerful (cars will gain a lot of braking grip as the speed decreases)