I know there are a few persons like me who wish to be able to drive magnificent and lovely cars of Assetto Corsa not only as much as possible on dry track, but also explore them further in wet slippery conditions a lot, master them. Maybe try to experience something similar to those exciting onboard videos from wet tracks.
All we can do is only wish and pray for the rain politely in a nice way, and maybe someday Gods will send it.
Maybe it would entertain Them if we would pretend that there was rain, and somehow track became all wet, reflective and slippery.
I know that it is not it, but if you'll try seriously, you'll see that it can be really good in this way too. How incredible it would be with detailed physics and visuals.
This is not actual wet physics, it is just lowered track grip and added reflections road mesh, it will not act as real wet track. The purpose is placebo, and "wet" pace, which is much slower than dry track, depending on temperature and water layer thickness a lot. Pretend that track is evenly wet, without rubber and oil on it, no puddles to cause drammatic hydroplanning moments (but it may seem like car is hydroplanning at some moments). Please try it, and you'll see that it is similar. I recommend using cars whose tires can take at least some slip angle.
You don't have to remove or replace anything in original files. This works as additional layout, it is basically just reflections mesh and lowered friction.
Just add files to original ks_nordschleife folder to their given locations, just a few files, will take less than a minute.
I recommend using green surface setting, dusty might be a bit extreme, but it would get a lot more grippy with more laps, though Nordschleife is very big track, so dusty might be bad idea.
Be aware that for the first few corners tires are cold, and you'll have to be very very slow through them, unless you'll use tire warmers. Also it will be hard to maintain optimal pressures and temperatures, because there is little grip, and tires can't deform a lot and collect all that heat. I wonder if it is the issue with real life wet tires. Worth noticing that it is just low grip, the tires are obviously the same, thats one of the main reasons why it is placebo mod.
In content manager there is possibility to set temperature all the way to 0 degrees of Celsius, this can help if you want track to be super slippery, for example like it is in November.
Here is a little guide for extreme conditions, have fun: