Stuttering when there's other cars on track

Either, but preferably when you are having most performance issues.

 

You could try changing the Use Thread from false to true in the controller.JSON.
rFactor2/Userdata/Player.controller.JSON.
Made a huge difference for me. It stopped all stuttering and it gave me a big performance increase. I can run 55 AI cars at La Grande track at 60FPS and all cars visible.
I've capped FPS at 60 so it might be higher than indicated. I have found the biggest killer of FPS is the shadows setting.
I have over 2000hrs on rfactor2. I have tried a lot of suggests for performance increase, this one has made the biggest difference. My graphics card is quite old now.
My system:
Windows 10-64
Intel I7 3.5
8 Gig mem
NVidia 460GTX 1gig
1 Screen 1920x1200
DX9
Your graphic card should give even better performance.
Found this suggestion on another forum.
Hope this is helpful. Pass it on if it works.