tyre/tire selection

[NaN]

outer ring of the wheel edge should vary more than the inner

From the code in mg_rim() the outer edge is:

Code:

innerRadius = rimDiameter_in * 0.0254f * 0.5f;
flangeOuterRadius = innerRadius * 1.08f;
float sectionWidth_m = sectionWidth_mm / 1000.0f;
flangeOutsideWidth = sectionWidth_m - (sectionWidth_m / 4.0f);

This means I always know the outer rim radius and width. The mesh will be placed relative to the outer rim edge. The inner rim edge has some constant values applied independent of the scale, thus unusable as reference point for mesh placement.

.blend file you posted has a negative x value for the hub. or, am i completely misunderstanding you?

Sorry, I've got the coordinates wrong. The wheel mesh is facing in negative direction(x-axis). Its vertices should be on the positive side then. Just import the 5_spoke_m.joe and scale the object (0.406, 0.406, 0.406). You only have to move the vertices (in edit mode) into positive direction(x-axis) and scale them by 1.05 or so. Then it should fit the rim pretty well. Undo the object scale and export the object.