I recall seeing some threads that highly recommend running the front tires at 16 and the rear tire at 18. The manual calls for 20 in front, 28 in the rear.
I have basically new 2018 RT Limited bikes. Wife likes to have her own.
I have installed comfort seat heated, the backrest that goes with that, and Bajaron swaybars. I am still looking for a bit more stability out of it, and have the stock tires on it (Kenda I believe is the brand). Little less than 400 miles on each one at this point. From reading threads on this site, there are some much better tire alternatives when replacement time comes.