I don’t really know why Hoosier recommend (and it’s only a recommendation) a 6″ wide front, just historical I believe. Certainly nothing structural or safety related. We are working with Hoosier and supplying them with our testing info. They certainly encouraged us to try both rims and were very interested in us reporting the results to them.
I have the height/circumference detail at work, but the difference is small. I’ll post it up as soon as I can.