Snippet of completed URDF specified toy car.

wheel_snippet.urdf

<!-- Left Front Wheel -->
<link name="left_front_wheel">
    <visual>
        <geometry>
            <cylinder length="0.05" radius="0.1"/>
        </geometry>
        <origin rpy="1.57075 1.57075 0"/>
        <material name="black"/>
    </visual>
    <collision>
         <geometry>
            <cylinder length="0.05" radius="0.1"/>
        </geometry>
        <origin rpy="1.57075 1.57075 0"/>
    </collision>
    <inertial>
        <origin rpy="1.57075 1.57075 0"/>
        <mass value="0.3"/>
        <inertia ixx="0.4" ixy="0" ixz="0" iyy="0.4" iyz="0.0" izz="0.2"/>
    </inertial>
</link>