The most efficient and fun way I can think of completing this achievement is by playing multiplayer and working towards the 'Full Medal Jacket
' achievement, which is to earn 325 medals in multiplayer. As well as that, chances are that you will take part in 50 races on Long Beach and 50 races on Nurburgring, netting you both 'Beach Hopper
' and 'Ringer
The best thing to do is to choose a class you want to race in and then choose a very consistent lobby car (or one you see regularly at the top of the leaderboards in Rivals for that specific class). Don't forget to choose a good tune before you take it online too! I find many of the cars are very good with a 'Tuned by Worm' tune.
While working your way to 325 medals, race one of these classes with your car of choice, and you'll eventually reach level 25 affinity with the car's manufacturer. Once you've completed one, switch class and choose a different car manufacturer.
For example, here's what I've been doing so far:X Class
: Lotus E21P Class
: #55 Mazda 787B (VIP Exclusive, thanks HolyHa1fDead for pointing it out!)R Class
: BMW M3 Race Car/#92 M3 GT2S Class
: Formula Ford
I'm still working my way to 8 manufacturers, but it's certainly more enjoyable to do it in multiplayer rather than driving round in circles or taping up your controller for drag races. Not only that, but it helps you earn other achievements online!
Hope this helps anyone, and if you have any other suggestions for cars to use or any questions, feel free to ask them in the comments