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
.)