After watching a ton of videos about iRacing and reading threads about it from the internet, I start to appreciate and love LFS more and more, iRacing seems like a ****ing arcade with neat graphics, but it seems like you can play it with a low-end pc too, so I bet not many of the cpu/gpu power will actually go towards calculating the physics... It looks like it's impossible to spin any car in that GAME unless you hit the grass. Also if you hit a wall there your car can fly anywhere, even 359253kmh backwards...
So, what I love about LFS then? It's cheap compared to what you get, think about paying 15 bucks for a track and 12 bucks per car in LFS.. believe me, LFS is cheap. Also it's only one time payment. You can play LFS with low-end pc, it has decent graphics, good variation of cars, very good set-up stuff and rather nice internet community altough there are some wankers even in this very forums ruining it.
And sorry, it's impossible to say it in one sentence