Crackdown 2

Just a quick little tiny hint about the race on Agency Island. If you're having trouble beating it on foot, a friend and I discovered that you can complete it in a helicopter. Saves time and frustration, it just requires a little patience squeezing into the tight spaces. Hope this helps a little!

*Edit* You can use a helicopter for any race you want, I just thought that most would need it for the Agency Tower race.
Also included is a YouTube video showing exactly what to do (Not my vid)

Credit goes to:
gamerzines on YouTube for making the video.
PatrickLiuX360 here for pointing out the video.
Gauderio for reminding me that this method works for all races.

I would like to add something to the above solutions which is that you can use the thrusters to assist you as you attempt the races. It as just as beneficial as using a chopper.

The thrusters do require the Toy Box DLC and Agility level 5.

Previous solutions for this achievement are excellent, and just wanted to add my quick perspective since I just got this last night.

There are 15 Rooftop Races in total. 5 are initially unlocked for you, then after getting those done, another 5 open up. Completing 10 will unlock the last five.

Races #1-10 are totally doable just running from rooftop to rooftop, made easier if you are fully ranked up on agility of course. However, races #11-15 are a bit tougher due to time constraints, and I would suggest using the helicopter for the last 5. If you are comfortable using the helicopter, you will be able to accomplish the last 5 somewhat easily, with the Agency race the trickiest. It has a time-out of 5:00, so you might not be able to finish it in time the first few attempts. Don't worry...just get used to sweeping the blades of the helicopter in and out over checkpoint spots to trigger them without hitting anything. Once you get adept at that, you'll finish the Agency race within 5:00 no problem.

There are 15 Rooftop Races in total. After completing 5 races, 5 more will unlock. Completing 10 will unlock the remaining five. I would recommend completing all of the races after taking care of the Cell Strongholds and after activating all of the Beacons. By activating the Beacons, the Agency Tower will become taller, making the race on Agency Island possible to complete.

And although they show up on your map, there are a total of 5 in Hope Springs, 5 in Green Bay, 4 in Unity Heights, and 1 in Agency Island.

The Agency Island race can be rather nerve-racking, but otherwise this is a very doable achievement.

Edit: Removed the bit about the invisible timer as there is now a visible timer. Also, using the thruster boots (Toybox DLC) will help out with the rooftop challenges.

Most of these are pretty easy and self explanatory but there are one or two tricky ones. The ones that come to mind is the agency tower one and one involving smokestack 's, the easiest way to do these (for me) was to grab a chopper and just fly from checkpoint to checkpoint.

Hope this helps if there is anything i can add/clarify please comment and let me know.