Can I complete the achievement for stunt jumps?
Solution 1:
I've read if you do the Downtown Underground race, you can get credit for 50 jumps off the one jump located during the race. More than a few people simply looped back some 49 times to perform the jump and get the achievement.
I will say that I gave it a quick try in a bike, and it didn't work for me, but others said it worked fine in a car. Hopefully it allows you to knock it out after 3 quick passes.
Here's a video of it in action -