This can be a quick and easy grind in conjunction with
First, you need (ideally) two people. Once you get to a spot where you need to load to leave/ enter like the elevator at The Tower or the Underground Parking Lot, you can continue to enter/ exit and then create a waypoint nearby - this should create a competition prompt that you then accept and your partner accepts. For this achievement you only need to take part, not win, but one of you does need to complete the challenge for it to count.
The reason for entering/ exiting is that it seems these show up at random on a timer, even when the challenges are set to frequent. By reloading the area you are resetting the timer and it will try to apply a challenge to the first thing you do, in this case a race.