# Why are my Box2D wheels slipping on ground?

I have a car, set up in Box2D as a rectangle connected with two wheels using WheelJoints:

The wheels are defined as follows:

    FixtureDef wheelFixtureDef = new FixtureDef();
wheelFixtureDef.density = 1.f;
wheelFixtureDef.shape = wheelShape;
wheelFixtureDef.friction = 0.98f;
wheelFixtureDef.restitution = 0.3f;

// wheel joint (only one of the wheels has the motor enabled)
wheelJointDef.dampingRatio = 0.9f;
wheelJointDef.frequencyHz = 20.0f;
wheelJointDef.motorSpeed = 15.4f;
wheelJointDef.maxMotorTorque = 100.f;


And the ground:

    FixtureDef groundFixtureDef = new FixtureDef();
groundFixtureDef.density = 0.f;
groundFixtureDef.friction = 1.0f;


Still, when trying to climb that hill in the picture, the wheels reach a stage where they just keep slipping, and it slides back down.

Why does it slip even though the friction coefficients are set high? How can I make it overcome that hill?

• Hi, how you generated the ground? – user3334375 Feb 13 '16 at 14:53