Heeeheeheee, didn't realize I was famous. I'll give you the advice I can, but a few people have already mentioned the key to the circular tests - careful throttle control.
When you're cornering - especially 'steady state' cornering like the circles - steering has as much to do with weight transfer as it does with aiming the front wheels. Once you find the proper steering angle, the car will drive around the circle without much steering adjustment.
When you accelerate, the car's weight transfers towards the rear wheels, giving them more traction, and away from the front wheels, giving them less traction. Of course, the opposite happens when you deaccelerate. Traction is increased at the front of the car, and decreased at the rear.
Once you find the correct steering angle, you can purposely balance the weight transfer with careful throttle control. Accelerate smoothly until the car starts to drift towards the outside (understeer). When that begins to happen, back off smoothly. This transfers weight forward, giving better traction up front and tightening the turn you are making. Once the car has begun to tighten up its turn and is beginning to point to the inside again, ease back into the gas. With practice, you will be able to balance the car at a good enough speed to pass the test.
I'll mention two other things -
1) The tests are HARD. I've barely gotten Bronze on most of them, and Silver on a few. Take your time and don't get frustrated. And really, practice getting comfortable where it is fun - on the tracks. The tests are great for teaching you proper form, though, so don't blow them off too long.
2) If you haven't already, bite the bullet and learn to drive using the analog sticks for both steering and throttle. It takes practice, but you can be much smoother that way. Blipping the throttle on and off gets the job done, but is much more likely to unsettle the car. Especially in something powerful.
Good luck and stick with it! Practice is the key. I'm still having trouble with my S license. You'll get there. The important thing is to make sure it stays fun. If it is too frustrating, just go Free Run or something that is more enjoyable for a while.
