Something is odd in these settings (turn compensation and stuff). I am more than 10 years thinking about it.
To check the linearity I look at the arc direction gauge. The visual wheel I still don't get it and lately I removed from screen.
In my opinion the settings behind it and the way it works and effect the wheel drawing should be rethought and or rephrased.
I don't mean to be harsh and I can love without it but something is off and if nobody can easily figure it or explain it then it could be done better.

I wrote something about that in 2021, but you replied there so I'm not sure what issue there is now.
https://www.lfs.net/forum/post/1977600#post1977600

It actually isn't very complicated. Wheel turn compensation (which is recommended to be set to max) does two different things depending on if the game controller wheel turns more or less than the in-game car wheel.

1) Game controller wheel can turn more than the simulated car steering wheel:

Perfect match is possible.
Game controller wheel stops turning (a 'stop force' is applied) when simulated car steering wheel reaches limits.

2) Game controller wheel can not turn as much as the simulated car steering wheel:

Perfect match is not possible.
Non-linear approach is implemented.
Steering wheel turn amount matches in the middle, but simulated car wheel turns more as you increase the steering angle.

NOTE: This relies on the "Wheel turn" setting in Options - Controls matching your controller wheel turn degrees. E.g. if your game controller turns 900 degrees, then "Wheel turn" must be set to 900.

EDIT: If I am missing something, or some bug has crept in, I would obviously like to know about it. But when I have checked in the past, it's all working as it should.

Quote from Scawen :

I wrote something about that in 2021, but you replied there so I'm not sure what...

So, I did some more testing and I'm sure something is wromg with either the code or my wheel's communication with the game. To remove all sources of error, I checked my wheel "axis" for linearity outside of LFS. Everything is working as intended, full range of motion and functioning bump stops if you decrease lock via the Logitech gaming software. I also checked the functionality in other games. As far as I can tell, everything behaves normally (eventhough most games aren't as transparent about their mechanics as LFS, so take this with a pinch of salt).

The problems I mentioned in my previous post still persist and I found another issue. On cars with 900deg lock-to-lock the turn compensation does nothing which makes sense (yet I don't have linear steering). Things get weird if you go below 900deg. My testing-car (prev. post) at 540 lock-to-lock behaves very linearly at 0.00 turn compensation (?). The problem starts if I add compensation at around 30deg lock at my physical wheel (and the virtual one): At 0.01 the virtual wheel suddenly jumps to a higher angle (about 45deg) and stays there all the way to 1.00 compensation therefore decreasing linearity. This effect increases as I add more lock on my physical wheel. At 180deg for example I get around 270deg on the virtual wheel.

Additionally, I can't "activate" the bump stops in LFS even if I decrease my maximum lock at the tires to 10deg. I still get 900deg steering wheel rotation at my physical wheel. The "controller wheel turns" slider appears to do nothing for me.

I tested everything in the 2015 0.6J version to confirm my findings and found the same results.

What I suggest is some data collection from other Logitech G29 players to figure out if this is an issue with my setup or the game. If the issue can be reproduced we should create a seperate thread and figure out what's going on with the code.

Before I start up the other computer (with G29) to check, can I ask you to check with the official GTR cars?

They have 540 degrees of lock. You can see that in "Steering" (section of the Garage/Pits screen) some text:
Car's steering wheel turns 540 degrees (lock to lock)

I guess you see this same info text with your testing car, but please check to confirm that.

I suggest testing with an official car, or a specific mod that we all have access to, so we can compare results.

Quote from Scawen :

Before I start up the other computer (with G29) to check, can I ask you to check...

Took the FZR, default setup and 540deg.

Screenshots taken at 90 and 180 and 360 at my physical wheel, compensation is at 0.00. As I said, 540deg seems to be the "magical number" where everything (below 270) works.

I haven't checked here yet but I've been looking on the internet and apparently thing may be affected by a "Steering Sensitivity" setting in the Logitech software.

https://steamcommunity.com/app/227300/discussions/0/1639787494950318456/

EDIT: Also you may be able to check if the non-linearity comes from the wheel/driver software by looking at the raw output values at the bottom right of the Options - Controls screen. Those are the raw input values that LFS receives from the software.

Quote from Scawen :

I haven't checked here yet but I've been looking on the internet and apparently...

Seems like a good idea, I will check if I'm back at the screen. I remember there being some weirdness with the steering sensitivity slider in Richard Burns Rally

I turned the "sensitivity" slider to 50%, this restored linearity. Now the compensation works aswell, as long as the "wheel turn" is set to the correct value

Quote from Scawen :

I wrote something about that in 2021, but you replied there so I'm not sure what...

I remembered that conversation happened but forgot the explanation in itself. I think the wording is either too obscure to me or my English is not high enough (I use English non translated version), causing me to forget the way it works.
What are the intermediate compensation doing? Any curve or formula of what´s going on?
I also admit to very often using less controller turn than real life, and this is where it gets weird. Maybe were some different solution can be found.
Not a big deal but I don´t think a beginner can easily understand and I also think that a lot of seasonned player forgot about it....
Anyway it would be nice to have more clear user friendly or more synchronous to used wheel, but I can live without.
I hope my previous message did not feel too harsh because that was not the intention but my wording was not the best.

Quote from loopingz :

I remembered that conversation happened but forgot the explanation in itself. I...

I think I figured it out now. First of all, make sure that there is no software at play that changes the raw output data of your steering wheel. In my case the Logitech Gaming Software messed up the signal before it reached LFS. (For some reason "sensitivity" in the LGS means "linearity". Also 50% sensitivity somehow equals 100% linearity. )

Then make sure your physical wheel turn matches the setting in LFS and set the "compensation" slider to 1.00. If the car inside LFS has less "wheel turn" than your physical wheel, LFS will set up "bump stops" when you hit maximum lock. If the car inside LFS has more "wheel turn" than your physical wheel the game will compensate at the far ends of your steering lock. The steering will behave linear closer towards the center and less linear towards the end of your "travel".

You probably want to set up a specific profile just for LFS, since it's the only game that REALLY only uses raw output data from your controller. I found that most other games somehow filter the data before it is displayed on screen, therefore they seem to work better with some adjusted settings in your wheel setup software.