I guessed a fair portion of what you said, but thank you for the translation to clarify everything.
Try playing with the tyre grip and slip angle in Aubrey Windle's Grand Prix 3 Advanced Physics Editor and see what sort of results you get regarding wheelspin.
In the 1977 and 1985 physics that I am working on, I currently tentatively have the following tyre grip and slip angles:
1977 1830 -14.00
1985 1890 -12.25
Since your year of interest, 1981, sits squarely in between 1977 and 1985, perhaps this might help you a bit.
Altering the car weight distribution with the GP3APE will probably affect the ease and likelihood of either the front or rear brakes locking up.
Post Edited (05-23-03 09:04)