To easily get the achievement for popping twenty tires on gang controlled vehicles in sixty seconds, go to the stadium on the north island where you find General Daz. There are two or three gang controlled vehicles outside, and possibly two gang cars inside by the ramp. There is also a space in the back of the stadium with four gang cars in a row. Find one gang controlled car and bring it to the back of the stadium where the four cars are located. Just pop all four tires on each car to unlock the achievement. Note: This of course must be done after defeating Daz.