At first, buy a car that was originally D Class and upgrade to A class.
(I did this challenge with Nissan Fairlady Z '69 that upgraded to A class.
Cars upgraded to other class may be needed, "Holden Torana A9X" is upgradable to S1.)
Then join "Online Road-trip" with the car that prepared (upgraded from D to requested class).
This challenge seems to be done after finishing 1 "Online Road-trip Event".
If you play this game on Xbox One console, don't forget to snap this solution with TA App while playing to this challenge
(At my completion, there were no solution for this challenge so I couldn't do "Challenge Accepted!" achievement with this challenge