Performance of FSX is greatly affected by the amount of time CPU spending between foreground operation and background data scenery loading. The lower the framerate is set, the more CPU time is devoted to loading scenery and texture.
FIBER_FRAME_TIME_FRACTION is a direct command that helps tune the amount of time per frame that CPU runs fiber jobs. The function is not present in fsx.CFG by default. To use the function, one can add the following lines in fsx.CFG under the [Main] section:
[Main]
FIBER_FRAME_TIME_FRACTION=n
The default value of it is 0.33, meaning that the CPU will spend 1 millisecond to scenery loading in every 3 milliseconds of rendering.
Any value between 0.01 and 0.99 is acceptable. The lower the value, the better the framerate but also the more the blurry.
What is the best value that balances between performance and image quality for one’s system?
Some people reported that using a higher value renders better photo quality scenery. Others said that this command has no real impact on FSX SP1 or later.
Still testing the usefulness of this command. Obviously, this is another tweak whose effectiveness can only be confirmed by extensive experiments.
FS Times 
Revisiting this a whole decade later and I can say that it makes a consistent and obvious difference on my second generation Ryzen based machine. I think the fact that modern CPUs these days have so many powerful cores compared to a decade ago, you can actually afford to significantly reduce the value of this parameter and there is still easily more than enough processing power to load the scenery on the threads running on those other cores. I can go as low as 0.05 and there is absolutely zero differences whatsoever in scenery loading or blurries (ORBX) but there is definitely a significant improvement in frame rate – about as good as turning off the road traffic and AI aircraft combined – so pretty huge for anyone familiar with FSX!
LikeLike
Well said, Jonathan.
CPUs today are far more advanced than those 10 years ago. Many issues affecting FSX and P3D should no longer be issues or significantly ironed on current computers with latest CPUs.
LikeLike
Have you done or hopefully concluded any more work on “fiber frame time fraction”. I love your work you have done here and can’t thank you enough for posting this sight. Your information has helped me tremendously and I appreciate it highly. So far everything that seemed pertinent to me and implemented has been a huge success.
LikeLike
Hi Rick,
Regarding fiber frame time fraction, no, I haven’t done more testings on it since I don’t find it having any effect in my setup — well maybe a little but I am not sure if it is good or bad. So I just exclude it from my fsx.CFG. I am afraid that you may have to test it yourself to see if it helps to your system.
Glad you find my blog useful.
Tom
LikeLike
Tom, just came upon your site. Good stuff. Thanks for the tweak info. One eternal question on everyone’s mind. How do you change the font size and color of the shift-Z text? This is what brought me to your site. Thanks again for any help. Brian.
LikeLike
Hi Brian, as far as I know that there is not any tweak that can change the font size and color of the Shift-Z text. However, I remember seeing some comments saying that the paid version of FSUIPC might be able to change the color of the text. But still, size can’t be changed.
I guess you could get more information regarding your question from FSUIPC’s product website. Cheers
Tom
LikeLike