Go into control settings, advanced, turn your wheel far right, press throttle, make sure both bars are level.
If not then calibrate your wheel and pedals via control panel\game controllers. If both bars are still not level re-calibrate but don't press the gas pedal all the way down.
I did some top speed testing at Avus67 a while back.
For maximum top speed I had tire pressure maximum so that only the crown of the tire was in contact with the road.
I had zero front and rear.
I do not remember which car it was but it was not F3000. I think it was a GT mod car. Anyway I got uber top speed but terrible cornering and the car was wondering down the straight
Le Mans 77 is good for top speed runs but Avus67 has a longer straight road and you get to it quicker.