(sorry for my bad english)
I have problem in offline game when some car on track crash (with other one or to wall etc.). There is between 1 and 13 fps. It occurs only on my desktop (AMD Phenom II X4 965 (3.4 GHz), 4 GB DDR3, GeForce 275, Windows 7 Ultimate 64b). On my laptop it is ok, no lags (i5-2410M (2.3 GHz), 4 GB DDR3, GeForce 540M, Windows 7 Home Premium 64b). I tried to re-intall (remove from registry too) and setup lower details and it had no effect. Any ideas?

Is there a difference in window mode?

Do you happen to 'force' some graphics settings for LFS? I can remember I've had this too when I forced AA and AF via the graphics control panel.

There is no diference in window mode.
Nothing happen ign lags, when I turn off AA and AF via game menu and via graphics control panel.
I think, it can be some bug in game, because when i save log from nvidia system monitor, graphics card and CPU was used between 30 and 50 %.
I'm going to try re-install graphics drivers and try setup their settings from laptop.

EDIT: problem solved. It was in graphics drivers. After re-installing gr. drivers it is ok. Thank everyone for help.

EDIT2: And it happen after installation ioCentre from Genius (mouse drivers)

Edit3: I don't know, why it is. After PC reboot it is lagging again. But re-install graphics drivers helps.

So now you reinstall the driver everytime you boot up?