On node '0' you can find rim radius: [Node] // 0 Geometry=(0.16,-0.22,0.015) Rim radius is 0.22m If you've got n+1 nodes, the node 'n/2' determines tire radius. For 61 nodes: [Node] // 30 Geometry=(0, -0.32, 0.091) Radius is 0.32m The first parameter of Geometry=( x, , ) is half of the width on each node.
I think you can't set it directly, it depends on construction and materials. But you can use the 'tire tool' to check how pressure and other variables change tire size.