What kind of fps are you getting now?
Back a while ago, on my old pc, I could only get about 25 fps and that would drop in traffic etc - almost impossible to drive ....
While in your car, hit (in English) Escape -> Options - > View -> click on Custom View and then set "render" = "none" .... that is, no body/ no wheels. This increased my fps by about 10.
Also, as mentioned go to Options -> Graphics ......
User, Mirror and Dust - low as you care or can
Haze - no
Shadow, Sky, trees, flags etc - off
Anti-aliasing - none
Texture filtering - none
Also go to Options -> Misc ........
Multiplayer car draw - set as low as you can
Dynamic LOD reduction - set as high as you can
If you have a choice of monitors - use the smallest screen you can and/or set LFS display resolution (Options -> Screen) to lowest that works for you.
That's all I can think of