Hi guys!

I am new here and checked the site but couldn't find any tweaker program and non-official websites aren't quite trustworthy so is there any tweaker program that i can download on here?

Yes,there is - https://www.lfs.net/file_lfs.php?name=LFS_EDITOR_7C_setup.exe
However you need an S3 licence to use it,there are no other options.

Quote from Eclipsed :

Yes,there is - https://www.lfs.net/file_lfs.php?name=LFS_EDITOR_7C_setup.exe
However you need an S3 licence to use it,there are no other options.

got it so it also allows you to tune engine stats, tire dimensions etc. right?

Yes.
Here is tutorial how to change engine:

But it can do more than tweaking engine or rims.
It is the full editor system, same as was used for the original LFS cars.
So you can make completely new cars. (but that requires some learning)
See https://www.lfs.net/files/vehmods for list of stuff that people made.