Mission 1 - "Pit Stop"
Wait until you get to about 3rd gear and the field isn't zipping past you dangerously. Slowly move your way up about 3/4 of your way down the short stretch there and if you do it right, 7th place on back should yield to you but the front group will still take off. FIRST THING you want to do is open your quick tune menu and turn off ASM. That kills a lot of speed in the corner that it doesn't need to kill. If you have problem controlling the tire spin, keep TCS on until you reach about 3rd gear, as above, and then turn it off quickly. ASM and TCS both scrub speed that you can hold through the turns. From there, it's all about getting the slip stream. The A.I.s break going into the corners if they're going too fast, so that's a golden opportunity for you to blow past them, as you don't need to slow near as much, if at all.
Mission 2 - "Indianapolis GWC"
Again, Slip Stream is your friend. ASM and TCS will cause you nothing but issues - you're going fast enough through these corners that you shouldn't need either. You don't need to hit the breaks hard going into the corners either - you should be able to cruise around them doing 170-180mph (270-290k/h), minimum. Tapping the brake and keeping about 25% throttle or less to maintain some momentum will be enough. Once you get the lead, keep an eye behind you to make sure they don't try to sneak past you on a straight, but for the most part, you can take off going into the corners.
Mission 3 - "Daytona GWC"
Same as above, minus the part about breaking. Also, make sure your ASM is off, and you should be high enough in speed already that TCS can be turned off with no problems as well. The A.I.s will brake going into the corner if they're doing more than 215mph (345k/h). Slip Stream behind them on the straights and dive low (or high, if the lane is wide open) going into the corners, but keep the gas floored - your car can handle it. If the next group of cars seems to have pulled away, suck up to the back of another car and push it (not slam it). Both you and the car your pushing will go faster without losing the draft, and you'll both catch the group. Just remember that the car you're pushing will brake going into the corners, so break away at that point.
The challenges really aren't that hard - course, I'm saying that as an American who kept buying the NASCAR games, so I at least know how the cars handle. Slip Stream and knowing that you're driving a near 2-ton brick at 220mph and treating it with the appropriate respect are what's key to winning with NASCAR. Course, a little luck doesn't hurt either.
One time I did this and the car completely flipped and ended up on it's roof. Next thing I knew the Rollover trophy message popped up.
