OK I'm going to assume that you're talking about the Gran Turismo 3 A-Spec Official Strategy Guide seeing as I borrowed the same guide from my friend.
This is what it says for IB-2:
Much easier that IB-1 because of the larger turning radius, but still a difficult challenge in its own right. Grabbing the bronze is simple. If you look at the times, there's almost a complete four second difference in the two scores. For the gold, you're literally going to need to knock the cones over with the air from your front fender, if you catch our drift. In other words, ride the center curb as much as possible to gain traction. Do it without actually knocking over the cones however, or you'll fail. Throughout the entire test your speed should drop no lower than 72MPH and climb no higher than 82MPH. And don't forget about your little "turbo boost" when the end is near.
Basically what this means is that nearing the end of the test don't keep so close to the curb, instead hit the accelerator, using the whole track to your advantage, to gain a better time.
