Forza Motorsport

You can select the worst lap time and do 20 laps with the same rival. It is not necessary to change rivals or circuits.

You can rent a car if you don't have one powerful enough

I did it in Class X on the Indiana oval This takes approximately 45 seconds per lap.

Go Into race and then Rivals. Pick any track. In setting, change Global Assists Presets to Maximum, then change Throttle to Assisted. Start the race, let the car do most of the work and use the accelerator if you need a boost to beat a rival. Once you can't beat the rival easily, back out and choose a different track. Keep doing this until you earn the achievement.

You will also unlock the Amateur Rival achievement


You will also unlock the Experienced Rival achievement


Here's a video Guide :

Go Into race and then Rivals. Pick any track. In setting, change Global Assists Presets to Maximum, then change Throttle to Assisted. Start the race, let the car do most of the work and use the accelerator if you need a boost to beat a rival. Once you can't beat the rival easily, back out and choose a different track. Keep doing this until you earn the achievement.

You will also unlock the Amateur Rival achievement


You will also unlock the Experienced Rival achievement


Here's a video Guide :