I play LFS at 1620p using nVidia DSR, runs smoothly, 60 fps with vsync
I play LFS at 4k using nVidia DSR stutters like crazy, 60 fps with vsync.
I also find that when it stutters, it goes up to 61.X fps
nVidia adaptive vsync via nVidia inspector is disabled.

Hmmmmm.....

Processor, Ram, Video card, Birthsign, Provide this info and we'll try to help.

LFS at 4k, Yes, that may be the issue, 1620 works (why not 1080 ???)

i5 6600
8gb Ram
GTX 970

I like better image quality. So thats why no 1080p.

It's LFS...........

I do understand the image quality thing but the graphics here are 8 years old. There has been very little (none) work on graphics for cars or tracks apart from S3 stuff and Westhill.

I don't know if 4k for LFS will do it any favours

LFS is really not a graphics wonderfest, it's more about the physics and VR, and VR is a graphical blackhole atm.

That will change in the future but ATM.........

Using SweetFX, Kit Hakodesh 2016 textures and keiichi shaders. Sorta like my version of a less intensive ENB with no depth of field.

Quote from Racer X NZ :

I don't know if 4k for LFS will do it any favours

4K used as a super sampling helps reducing shimmering, which is really present in LFS (and LFS dosen't have a temporal antialiasing solution to really fix this)

And do your suggestions fix the stuttering issue with 4K?

It may be a vram issue with the 970 and it's take on 4gig of ram.

Try 1080 with the above suggestion of sweetFX etc and see if that's ok.

Not VRAM, 1735 mb used on multiplayer 39/40 cruise server, monitored using msi afterburner. Looks like I may just play at 1440p instead now.