Strange stutter behaviour with minimal FPS drop

[The Roo]

Hello everyone,

So, I have been thru a lot of posts and tried a lot of things, but haven't found a solution as yet to my situation.

Simply put, what I currently have is if there is ANY FPS drop (I mean 1 or 3 fps, that small) I am getting stuttering in Iracing. I have it set to a limit of 160 FPS for my 180hz monitors, and it runs just fine...but the moment it drops to 159, 157 or whatever (standard FPS fluctuations), there is a stuttering effect EVERY time. I kinda thought this is exactly what G-sync is supposed to manage and make imperceivable!

A small backstory...I didn't notice this happening (my system is only 2 months old) but maybe I was just not paying enough attention...and then I changed a couple of in-game settings and also dropped the power to the GPU on a friend's recommendation to try and give the GPU more overhead as it was running close to 80'c. It was after this I think the issue arose. I have since put every in game and windows/NVCP setting back exactly where it was, no luck. Installed latest NV drivers, no luck. Re-did in-game graphics config, no luck. Tried all combinations of v-sync, g-sync etc etc, no luck.

I am absolutely at a loss as to what is happening. a 2-3 FPS drop should NOT be causing this in such a high end system (5090, 9800 X3D).

No cores a parked. Performance settings are all right. I am just out of ideas and was about to try Nvidia to see if they could help, but thought there is likely more chance and assistance on here!

Any thoughts or help would be MOST appreciated!

Thanks

TR

[Chief Blur Buster]

Ideally, a proper framerate fluctuation slightly below cap (e.g. 159fps instead of 160fps) should result in only a (1/159)-(1/160)= 39 microsecond jitter during VRR that is theoretically invisible.

But a dramatic stutter during a framedrop means VRR is probably not working properly.

Unfortunately, I've heard of Windows 11 VRR bugs in 24H2 and 25H2.

Pass 1: Sanity Check Step
1. Before you do anything else, prioritize on verifying VRR is working, e.g. test using Pendulum Demo, and other apps to visually verify that VRR is working properly.
2. THEN, follow the below steps.

Pass 2: Game Optimizing Step
1. Try full screen exclusive mode (not borderless, or fake FSE).
2. Disable "Fullscreen Optimizations" temporarily to bypasses the VRR bugs.
3. Single monitor mode only
4. Verify VRR is enabled in your monitor menus
5. Try slightly shallower frame queue (1 frame, use NULL settings).

Pass 3: Try different capping algorithms
- In-game framerate cap (less lag but more stutters).
- External frame rate cap like RTSS (more lag but fewer stutters) since those frame rate caps are microsecond accurate.
- Or even concurrent dual framerate cap approach
......Latency-reducing framerate cap in-game
......Stutter-reducing framerate cap external (RTSS)
......IMPORTANT #1: Make sure they're not identical but at least ~0.1 to ~1fps different. Usually it's better to put the latency-reducing cap lower than the stutter-reducing cap.
......IMPORTANT #2: Both caps should be at least 3% or more below VRR maxHz.

*TIP: Excessively large queue sizes during VRR can mean the frames can buffer up during the VSYNC-behaving cap, and "suddenly release" when framerates fall below a cap or VRR maxHz = bigger than normal stutter when framerates fluctuate below MaxHz or certain kinds of external caps. Not all caps will cause a frame queue to clog up, but caps can do this effect. That's why I recommend zeroing out the frame queue to smooth out those "framerate fluctuations below caps" = a bit more stutters during max cap, but less stutters during fluctuate below max cap = tradeoff that needs tuning. VSYNC ON will use the full queue, while VRR will literally empty the queue = multi-refresh-cycle stutter during framerate yoyo. This also produces the historical latency yoyo of framerates at VRR MaxHz versus VRR below Hz, which is solved by capping or solved by using a monitor high Hz enough to allow a frame rate range range to organically fluctuate completely inside your VRR range.