Numerical simulations are performed to look at the evolution of the 1866 trail of Leonids. Parallelized computation with 250 processors in CINES (France) allow us to have resutls in only 4 to 6 hours. We showed that the trail is partly and periodicly perturbed by Earth, during close encounters. Features of ejection velocity and angle (perpendicular or in the cometary orbital plane) depend on the year of the shower, and tend to be more diluted with time after comet return. With a cometary dust emission model, that still has to be improved by some measures (especially [Afρ]), we deduced a "weight factor" for each simulated particle. Computering the particle density in Earth neighbourhood at the time of the predicted maximum of the shower allow us to predict a ZHR of 2850, on Nov. 19th 2002, 10:36.