Awesome track, nice to get old tracks to drive old cars in AC :) thanks.
And as homecalendar, I believe the bumps are a bit too rough, perhaps track meshes are a bit too low poly or my G-25 settings are not (and probably far from) perfect.
For instance the Lotus 49 goes a bit left and right in straight line, nothing crazy and it's quite easy manageable, it's just behave this way. Whereas it is less noticeable with the Carrera RSR.