LFS probably has the most accurate representation of grip there is TBH, although as already mentioned, the way you lose grip very suddenly sometimes is a little odd, but on the whole if anything, LFS has too much grip in comparison to real life, although the feeling of speed is a hard thing to achieve on a computer simulation, you cant expect a car to turn into a tight corner at 70+ mph and expect it to hold, because it just wont in a realistic situation, simple as.
And the source of this info?? Myself, having driven a lot of vehicles on a lot of different surfaces in all manner of weather conditions, so i know it's about right, if a little strange with the sudden grip loss sometimes.