I dumped the 21” UT tires/wheels from my PMY for some 18s from TSportLine. So when I asked them what wheel setting I should use they said to just leave it on 21”. Looking at tire specs on Tire Rack there wasn’t significant difference in rolling distance between the 21” Michelins and the 18s.
I did do some BEFORE and AFTER testing with my DRAGY and the speedometer read exactly the same at speeds up to 80 mph. The upside is my Y is more efficient and faster than it was on the 21s and I no longer live in fear of curbs or potholes.