I think it's another lucky based achievement in this list. There are 2 ways to obtain it.1. Car Drop (not recommended)
This is confirmed, but this is extremely rare to find a spot with a 10th level car. I found one at the top of the Bamburgh Castle when I have nearly done "100 spots" achievement.
If you are not good with driving and winning races you can try to find it, but it might be test for your pattience.
It's not recommended but if you want to do it through car drops try to start at locations where is more than 1 drop spot (Bamburgh Castle, Mudkickers, Mortimer Gardens, Quarry) 2. Races
You can upgrade your car by winning Head-to-Head races. After you beat your rival you'll get a reward. In a voting you can choose with your D-pad one of two cars or channel exchange.
The best way is to find on the map car with the highest level and then win a few races.
How many races do you have to win ? It depends on yours starting car level and on your opponents and their car levels. In my case I found a level 7 Bentley just after the game started and I had to win 3 races ( every opponent had lower car level than me )
- If You win H-t-H race against lower lower car level you'll get as reward car with your's level + 1
- If You win H-t-H race against the same or 1 higher car level you'll get as reward car with your's level + 1
- If You win H-t-H race against higher car level you'll get as reward car with his level.Some race tips
This might be tricky. Lower level cars mostly have good handling but are slow. You have to start h-t-h at the right direction or you might have trouble to win. At the start races have long distance (4-6 km), after some time races will be shorter, so you have less time to fix mistakes.
The most dangerous part of this is when you'll get car with 9th level. They are very fast but also very unstable on the grass. I had some 9th level cars like Lamborghini or Ferrari and they are speed monsters but hardly to drive in this cirrumstates.
You have advantage with power, drive carrefully with no maximum speed. Be carefull at jumps, they are really dangerous.
There some extra tips for race strategy from ScorchPSO
Good luck, it will be needed here