This is for a streetable muscle car IRS application.
I'm looking at the amount of track width change, per inch of wheel travel (near normal ride height).
How much change here is acceptable or terrible? 0.050" per side? 0.100"? 0.500"?
I understand that the less this figure changes, the better. But I measured my chassis and infinity-length lower control arms won't clear the oil pan.
Geometrically, the amount of scrub is a function of lower control arm length, spindle height, and upper control arm length, and thier location relative to another. (duh.)
Those things are all driven primarily by roll center location, camber gain/loss, anti-dive, castor, etc. These things have a direct and obvious impact on handling performance and car 'feel.'
Axial/track scrub does not, particularly... as the displacement per tire revolution as your suspension cycles is so small it doesn't create a significant lateral force. At any rate its importance in how your car handles is an order of magnitude less important than the above factors. This is true, I think, for the axial scrub you will see with a reasonable length control arm setup.