# Custom Tire Force and Torque

Compute interactions and spatial relationships between tire and ground surface

*Since R2024a*

**Libraries:**

Simscape /
Multibody /
Forces and Torques

## Description

The Custom Tire Force and Torque block computes the interactions and spatial relationships between a tire and the ground surface.

To model a custom tire, use the outputs from the block to compute the tire force and torque. Then, loop these signals into the block as inputs. The image shows the diagram of a custom tire model.

You must calculate the tire force and torque relative to the contact frame of the tire.
The contact frame is at the contact point and the *z*-axis of the frame is
perpendicular to the contact plane. The tire force must be nonnegative. If the tire force is
negative, the block clips the input force to zero. Additionally, you must maintain consistent
units for force and torque throughout the simulation.

The follower frame is at the center of the tire. The image shows the follower and contact frames of the tire at zero configuration.

The yaw, camber, and spin angles correspond to a
*y*-*x*-*z* sequence rotation about the
follower frame of a tire.

The block has two methods to calculate the data that characterizes the interactions and spatial relationships between the tire and the ground. The closest point method determines the contact point by finding the point on the ground surface that is closest to the center of the tire and lies in the plane of the tire. The contact normal vector is at the contact point and perpendicular to the contact patch at the contact point.

For scenarios where tires experience multiple-point contact, such as off-road terrain or obstacles like speed bumps, use the weighted-penetration method. To simplify the computation due to the irregularities of the contact surface, this method computes an equivalent contact plane at each simulation time step to approximate the actual contact area. The contact point is the nearest point on this equivalent plane to the center of the tire. The contact normal vector is at the contact point and perpendicular to the equivalent plane. For example, the image shows how the weighted-penetration method computes the equivalent plane, contact point, and normal vector when a tire encounters a ramp.

The weighted-penetration normal vector, *n*, is orthogonal to the
equivalent contact plane.

**Note**

When using the weighted-penetration method, the contact point may not lie on the actual ground geometry. For example, the contact point may be below or above the ground surface if the contact area is locally convex or concave.

You can use the **con** port to indicate whether the tire and the surface
have a valid contact. If the tire and the surface are not in contact or the contact is not
valid, all sensed outputs, such as the tire force, tire torque, and camber angle, become
zero.

## Ports

### Geometry

### Frame

### Input

### Output

## Parameters

## Version History

**Introduced in R2024a**