I also started making the lowpoly. I did this by just duplicating the highpoly model, deleting the turbosmooth modifier and then just removed loads of edgeloops. I got the model own to 57,000 tris which should be completely fine. I will just have to see how rfactor runs when the models ingame. If it needs more optimization I could easily go back and delete some more loops.
And here's the high and low poly next to each other. High on the left and Low on the right.