I'm just changing my grass using some free res. Would like to ask what are these "name_su.nif". It looks like "name.nif" mostly . What role do they make in game ?

Short story.
I'm in the middle of Caught in the Hunt quest. Have 3 good saves : one - before the quest is started, 2 - just before first meeting with Kurdan , 3 - just before the travel to Fort Grief.
1. I changed following grass meshes


All three saves work fine
2. I changes this meshes again and added another one.

All look correct in Nifscope. The difference is part of new one are just a copy of another under new name (bwgroundcover02 == groundcovermediumgrass02 , bwgroundcover03 == groundcoverfern02su ).

Independent on the save I use I get CTD when the Fort Grief's terrain has been loading. Plants from two of meshes pack are presented on Fort Grief area (bwgroundcover03.nif ).
If I back to previous version of meshes all three saves work without any problem and I can kill ugly Kurdan (HA!).

Question is "Why ?"
Request is - If anyone knows good source of info about grass in this game (what does means this "su" suffix, how way the grass has been placing), please link.

I believe the "su" suffix stands for "summer".

If you look at the "textures\trees\leaves\.." folder, you'll see that trees have the same "su" suffix for some of the tree textures. BUT, this same folder for tree textures, also has "wi", "fa", and "snow" suffixes.

So, going by this, here's what I concluded:

"su" suffix = summer nif & texture (textures are much brighter and saturated)

"wi" suffix = winter nif & texture (when not actively snowing) (textures are duller and more subdued)

"fa" suffix = fall/autumn nif & texture (textures are duller and ore subdued)

"snow" suffix = a nif & texture for when it is actively snowing in game (textures have white snow on them)

It seems the nifs & textures without any of these suffixes, can be considered "Spring" season versions (textures are brighter and saturated)

I'm not for sure, but if Oblivion trees/plants don't change color from season to season in the actual game (I've not extensively played Oblivion, I just mod for it), it looks like the game makers were attempting to get such a seasonal effect to work, but maybe it never quite got finished nor made it in the game?

And again, I don't know if these seasonal nifs/textures actually work in the game, like they seem meant to.

Koniption

1. @Koniption
Hm maybe, but :
1. There is no other, similar suffixes I know
2. Some part of plants are designed for specific terrain (with "snow" included in name ), but a few only.
3. In fact important for visual aspect of this game are terrain and weather only (without mods).
4. Idea in 2006 (if I remember) Beth rides on old good Gambro was trying dynamic changing meshes ...It would be such beautiful catastrophe.
But, damn ,who knows ?

2. "The story" continuation.
I was thinking I had gave one texture for two meshes was the CTDs reason. But not. I've changed "mesh set" - all meshes have own textures. With old (but not default !) meshes I can leave Fort Grief , with new ones - cannot. I'm lost.