Hello
I use a Road King Classic for our Champion Escort sidecar. It all depends on why you want a sidecar. Our needs were for my wife who can not walk. After a lot of looking we settled on the Escort. I bought ours on ebay for 4500.00 used. Driving a sidecar is very different than riding a bike.
We had a 1994 HD sidecar rig in 94, because we wanted to take our girls with us. The sidecar will use more gas, and demand more power. I have two HD,s. One for me and one for my wife. Hope this helps.
Ken
Forgot to add a sidecar for a goldwing will not work for a Roadking