Circle of forces
（重定向自Friction Circle）
![](/Images/godic/202501/14/Circle-of-Forces5016.gif")
The circle of forces, traction circle, friction circle, or friction ellipse is a useful way to think about the dynamic interaction between a vehicle's tire and the road surface. In the diagram below we are looking at the tire from above, so that the road surface lies in the x-y plane. The vehicle that the tire is attached to is moving in the positive y direction.