Test Drive Unlimited 2

This can be done in ranked or unranked "Keep your distance" mode. You need to get 8 people in the lobby before starting. Stay within the order you start. All that is needed is to keep above 62MPH / 100KM/h and to keep each racer within the required distance of 10metres-54metres to the racer in front (All green dots on the list)

Great tip from TauntTitch87: Put the car on manual whilst using the Bugatti Veyron 16.4 Grand Sport. Hold trigger down and you hit 68MPH and go no faster. Nice and easy

Another tip from Spilner: Use the Pink Fastback you win from Miami, in 2nd gear it tops at around 80MPH. This tip is useful as you can get that car early in the game without much effort

We had the racer in front average around 75MPH and after about 30 seconds we all had the accelerator held in the right place so we were all at a steady speed. The achievement unlocks the second you hit 15 seconds.

If anyone gets too close or falls back too far then their tag gets a red light next to it so you know where it is failing.

***SERVER UPDATE: SOME TDU2 SERVERS ARE DOWN. As of around August 2014, it's been impossible to join/invite other players from the in-game menus and Club vs. Club matches are NOT working either. However, club invites and joining clubs are still working as of January 2015.***

Okay!! This one was an absolute pain, until we discovered a few very very important things. Here goes my solution..

For this achievement, you need to have 8 players, all in the same Follow-the-Leader race, at the required distance from each other, for 15 seconds. Then, Bing! Achievement.

For the best spot to do this race, on Ibiza, I recommend using the "Follow-the-Leader" multiplayer race that is lettered "I". It is about 2-3 miles South-East-East from the used car dealer in Ibiza, on the main road that heads east. It's a perfect long stretch for this achievement.
For the best spot on Hawaii, I believe the Follow-the-Leader race letter is "H", on one of the huge long elevated freeways that crosses the center of Hawaii, near the middle of the map.
The Follow-the-Leader icon is green, and has a car with an up and down arrow underneath it. You can find these by hitting "Back" and "RB" once to shift your map to Multiplayer Challenges/Races.

Now, on to the race!! And what not to do from our experience at the end of this, plus fun notes. :-)

What we did was use the level 3 club exclusive car the Ferrari FXX. It really looked beautiful, 8 FXX's all lined up.
The race is 2 minutes I believe, so you want to make sure you don't waste too much time or it will run out on you and you have to repeat..
Get everyone in the same race lobby, everyone select the same car(we used Ferrari FXX, level 3 club exclusive), and you MUST choose the same car, otherwise it will be an absolute nightmare keeping everyone at the same speed. I recommend, either club exclusive car, or a delta Lancia, or one of the other beginning cars, as long as no-one has added any upgrades to it. Buy a new one if you have to.
Once everyone is in the lobby, make sure everyone has changed their transmission to "Sequential"(same thing as manual!!), and NOT automatic. This is critical. Also, make sure everyone has full driving aids on!
"Y" shifts up a gear, "B" shifts down a gear. For the Ferrari FXX, 2nd was was required to get over the minimum speed. If you use a different car, test drive it in manual mode to figure out what gear will get it over 62 mph, the minimum.
Start the race, and have everyone shift into 2nd gear(or your appropriate gear), and then nudge up to the leader, who does not budge yet. I don't recommend actually bumping into them, but just get within 5-10 feet. Once everyone is in position, on the leader's go, the Leader hits the throttle to the max. Everyone else, as soon as you see the racer right in front of you start moving, hit the throttle to the max as well.
The leader is responsible for making sure the line doesn't go offroad(lol). Once everyone has reached max gear speed, watch the dots that show the distance between each racer. Green is good obviously. a great distance between racers is around 45 meters.
If someone has a red dot, look carefully to see whether the dot is above or below their name. The designated person who is directing the race then needs to tell the person above or below to either speed up or slow down as necessary.
Here's an example. Player 1, 2, 3, 4, 5, 6, 7, and 8 are racing. Players 1*2*3*4 all have green dots. Players 4*5 have a red dot. And 5*6*7*8 have green dots between them. Now, players 3*4 show a green dot and a distance of 30 meters. Players 4*5 show a red dot and a distance of 15 meters. And, players 5*6 show a green dot and a distance of 60 meters. P3 -- 30m -- P4 -- 15m -- P5 -- 60m -- P6.
That means that player 5 needs to slow down, and player 4 stays where he is. Player 5 needs to let off the throttle briefly, and then full throttle again, and repeat until it's all good. when it's good, it should look something like this: P3--30m--P4--35m--P5--40m--P6. And, it's all fixed! Of course, if the distance between them is OVER the correct distance, then just reverse the procedure. I believe the minimum is around 15-20m, and the max is around 70-75m. In actual experience, you'll have anywhere from 1-3 people with red dots. just understand how it works, and you're golden to fix it. :-) Once again, I recommend the person best qualified to direct this be the only one talking. That way, you all have one person to pick on if it fails. LOL. Seriously, it will probably help as long as they know what they are doing.

And, hold that correct distance for 20 seconds!! I say 20, because we had some people stop the instant their achievement popped, and half of the others didn't get it. The game is weird here, and you need to make sure everyone gets it first. Also, make sure that everyone is showing all green as well, as some people can show green while others have red.

Final notes--big thanks to lightsup55 for which races.. big thanks to Ice Maiden 87 for suggestion that we were using the wrong car.... and big thanks to everyone else who helped sort this slightly messy achievement out!

What not to do. Do NOT pick the Club car Apollo Gumpert S unless you want a UFO, or rather, UDO. If you want to see it, it won't show up. Seriously, we all picked it, and everyone was lagging ridiculously. Then we switched to different cars and eventually the Ferrari FXX, and we were suddenly lag-free!
There were some funny incidents involving very expensive Ferrari's in massive car pileups... I saw one once that suddenly shut off the side of the road into the bushes. I wonder if the driver got abducted by the UFO's we were using earlier....
And, have fun! Hopefully this helps you get this one as pain-free as possible. It took us over an hour and a half to get it all sorted out.