public void ApplyWheelConstraint(Wheel wheel, float dt)
{
    Vector offset = ToWorld(wheel.mPosition);
    Vector groundVel = PointVel(offset);
    Vector patchDir = ToWorld(wheel.PatchDir());
    Vector constraintDir = ToWorld(wheel.ConstraintDir());
    Vector deltaV = -groundVel.Project(constraintDir);
    Vector dir = deltaV;
    float mag = 0.0f;
    dir.Normalize(out mag);

    if (mag < 0.1f)
        wheel.mStaticFriction = true;
    else if (wheel.mStaticFriction)
    {
        float acc = wheel.mAcceleration.mValue.Length;
        float maxAcc = cGravity * wheel.Friction();
        if (acc > maxAcc)
            wheel.mStaticFriction = false;
    }

    mag *= wheel.Friction();

    Vector impulse = ChangePointVel( dt, offset, dir, mag );

    wheel.mAngVel = groundVel.Dot(patchDir) / wheel.mRadius;
    //wheel.mAcceleration.mValue = deltaV / dt; //Direct
    wheel.mAcceleration.Add( deltaV / dt, 0.2f ); //Interpolated
}