About the research using a car tire on the rear. I have had many bikes over the years and they were all metrics. This is the first harley.
Past three metric I installed a car tire. The car tire once you find the correct air pressure which does not take very long reacts mush like a mc tire. Last bike was 2013 yamaha 1300 tourer with all the goodies. Ride two up most of the time. Road the bike for 10 months. I am a very easy rider which my friends make fun of. That rear tire lasted 6100 miles bald down the middle. Installed a car tire put on another 13,368 miles. Lost 3/64 of tread. Original tread depth of the car tire was 11/32. MC tire new was 10/32 tread depth. The thread area of the car tire was 6.5 inches. On the ground 4 7/8 inches. When corning at speeds above 40 the tire rolls up somewhat like a mc tire but there is still a lot on the road. Taking really twisty roads and being to corner at speeds where the flood boards rub the ground at 70 miles an hour never slipped once but had a couple of friends go down but not killed. Speeds below 40 some turns where a little harder to make but not enough to worry about. If it was my wife would have slap the helmet. Never worried about stones or other things on the road. Needed to pull off in a hurry to avoid a car many times in the stones no problems. Most of the time kept right on accelerating. Lots of rubber on the road when it is raining also.
For reasons mention above and a few other reasons and my years of experience with a car tire I feel safer with a mc tire.
This is just my opinion you will have to do your own research like I did 16 years ago.