Crackdown

Use the car which is in the achievement picture and drive to the first island, once there go on the beach at the bottom. Drive towards the peer and you will see a ramp of sand up against the wall, drive as fast as possible and your car will be able to complete 3 flips easily

As shown in the achievement picture, this one is most easily done with the dune buggy, which was released as downloadable content.

The easiest way to accomplish this is to have beaten all of the Shai-Gen bosses. Take your dune buggy to where you defeated Col. Axton Cowell (the building directly across the large courtyard from the final Shai-Gen boss). Drive your dune buggy into the elevator and take it up to the top. Then proceed to pick up and throw your dune buggy up the various levels until you reach the top. Get in the dune buggy and drive it off the balcony. The small lip should cause your dune buggy to start flipping end over end. There should be just enough heigh to complete 3 full flips.

YOU MUST HAVE 4 STARS DRIVING AND YOU MUST USE AN AGENCY SUV! YOU DON'T NEED THE DLC.

This is done on the highest building in the game on the last kingpin Wang's building.

The text in the video below reads, "Jump to the glass using B, then when driving up the building, keep B down until you hear the suspension give way, then loose go and press B down again. It'll take some practice, but you'll nail it."

After about 45 minutes of trying to get this to work I finally got it. None of the other solutions like the truck ramp were not working for me. This was obviously my best bet. Follow what is in the video.

A few tips that I had to figure out the hard way because the video didn't include it in the text...

1: If you fall off turn on your back so that the car doesn't hit an object with the bottom middle part of the cars body. If you do hit the middle it does A LOT of damage.

2: You have to press B immediately after you hit the glass or else you will slide off.

3: Try to release and press B by using the sound. Just a little before the sound ends. If you do it by looking at the screen and not listening you will fall because you won't notice soon enough.

4: Do frontflips, I spent the majority of my time doing backflips once I tried front flips I did it in 10 minutes as opposed to the 30 I spent back flipping and not getting it.

5: Jump off RIGHT before you hit the top THEN start the frontflip. If you don't let go of B before you hit the top it'll take to long for you to start turning for the frontflip and you wont be able to get 3 flips, so you want to let go RIGHT before you hit the top; takes a lot of timing though.

6: Shortly after you get on the building there will be two chinese letters on the building, go to the left to avoid them then move to the middle once you get past them. They are they only obstacle in your way.

7: The quickest route to get to the building is this, ( if your're like me your vehicle will blow up and you will kill yourself and spawn at the agency.)

Go to agency then get an SUV.
Go through the agency tunnel marked with the number 3.
Go onto the road in front of you and a little to your right.
Keep going straight until you see the tunnel in front of you then take a left inside that tunnel.
Once out of the tunnel go right.
Go straight until you see you're first right (Not the bulding entrance.) Then take that right.
Follow that road (the road will take you left) then go into the tunnel toward your right.
Take your first right in the tunnel.
Once your out the building should be on your left.

BTW, it seems like it takes a long time from the directions but after you figure out this route it should take you 1 and a half minutes.

You don't need to have the DLC to get this achievement -- I got it using a 4-star Agency SUV and a ramp truck near the agency exit on the first island. Set the ramp truck on the freeway on-ramp and get lots of speed, then launch off and do the flips.

Not the easiest method; took me several tries before I got a good aim on the launch! This video shows the location, though you can't do it in Keys to the City, of course.

Skip the elabourate set up! Just take the agency buggy to the stadium more or less in the middle of the North Los Muertos Island and get a good run at the hole in the roof. I actually managed to almost pull off a fourth backflip.

Thanks to Sinnott147 for mentioning that I should be more specific about the location.