# About physic calculation of wheelcollider

I try making simple car with wheelcollider. But I don’t understand about friction calculation. (I have read it already.)

I think that “Slip” means relative velocity of tire and ground so if the slip is more that extremum, the force must be constant right?

first I try motortorque = 50 with stiffness = 1 and try with stiffness = 0.1, result is the car is slower, so this mean stiffness=0.1 is not enough for 50 motortorque and the tire slip too much right? And then I increased motortorque to 500, but the result I got is faster.

Hi

stiffness is used to simulate ground material so you probably want this to be the same as your ground material’s staticFriction. I do not recommend to change this value to affect your velocity/torque.

You have to play around with the values for motorTorque to find something that fits your needs.

You can think of it as a real car. To say simple, your wheel will spin faster if you higher the motorTorque value. If you have a high friction this means you go faster.

If you need any more help please try to be a bit more specific.