Is 20w 5o oil only for Honda goldwing?

No, it can be used in any gas engine. Yes cars also. I use 20w 40, it covers all my driving needs. If you drive in a very hot climate, 20w50 is good. If you drive in a cooler climate, then 10w30 is good. Usually for us bikers we don't drive too much when its freezing out, so, 20w40 is good from 20 degrees f right up to and over 100 degrees f. If you live in the deep south I would go with 20w50.