To think about: there is SAE paper on rim types----motorcycle rims/bead are different than car rims/beads
#2 bikes lean in turns and mc tires are designed for this, cars and their tires do not lean.
Beads not being the same scares me and I lean.
I once bought a HD 45 WLA with junk yard 18" tires, front and rear=not rideable until proper motorcycle tires installed------my MZ sidecar outfit had 15" 2CV tire on rear but with special rim--worked great sidecar but solo not fun/safe to ride and against law or insurance to ride in Germany. Tried it on test rides, solo=not fun.
SilverWing handles bad enough with perfect fresh mc tires----hate to see what could happen with car tire on rear.
In spite of bike tire expense I will stick with mc tires-----24,000 scooter miles ridden in 2014. My life valuable to me.
But I see for fat Goldwing Riders//fat Girlfriend/trailer car tire sounds good and they don't lean much in turns anyway... but not overloaded/proper inflation bike tire still safer.
Think the whole thing is about longer tire life. Short tire life one of the facts of life if you ride a lot on 2 wheeler