Hall of Famer Achievement
Hall of Famer25
Reach Driver Level 150.
The leveling achievements should all happen naturally as your work on other achievements in the game. XP is awarded based on the length of the race rather than the difficulty, so changing the assists and Drivatar difficulty does not impact how fast you level up.
To determine how XP is needed for any given level, the formula is (Level x 14,000) - 10,000. For level one, you therefore need (1 x 14,000) - 10,000 = 4,000 XP.
If you want to level this up early rather than waiting, I suggest using the AFK method detailed in the guide for leveling up your affinity with manufacturers:
From the main Forza screen, choose Multiplayer, press to create a private match and to confirm. Once the vehicle selection screen opens, choose a car that is rated B or below. At this point you will be in the lobby, so press to change the options to match these choices:
Game Type: Drag
Track: 8-player 1-mile drag
Max Players: 16
Max Drivatars: 15
Drivatar Difficulty: New Racer
Car Class: Any
When you go back to the lobby, all the Drivatars will have a class of car that matches yours. Press to go back into the settings and change your car to the highest rated vehicle you have from the manufacturer you are going to focus on. You will end up back in the lobby with your fast car racing against the lower rated vehicles the Drivatars are using, making the drag race basically an automatic win. Now have the right trigger of your controller compressed (use a rubber band or even the cord to your headset) and the car will automatically accelerate down the track, winning every time. It will take approximately 10-15 minutes to complete the 10 heats, at which point you will be back in the lobby. Press to restart the process.
XP rewarded: 10,000
Note that the achievement actually requires you to complete a race while at this driver level, so it will unlock at the end of the next race after you reach level one hundred fifty.