Factory Driver Achievement
Get any Car Manufacturer to Affinity level 50.
I can guarantee you that this will be one of your last achievements, as this is rumored to take absolutely forever. Even Turn 10 stated that their goal was to have less that 1 percent of people attain this in under a 24 month period. I for one don't think that it will take that long. Just stick to races that net you bonus Affinity points, and of course, try to stick to only a few of the manufacturers. Stay loyal!