game is lagging, low fps

Hello! When im playing the game , i get low fps, around 20 FPS when 1 car running.
What can the problem be, i have all options on the lowest and turned off the effects, i play with 1440x900 .

Specs:

CPU: Q6600 (4 core at stock speed)
GPU: Gtx 550Ti
Ram: 4GB 800mhz DDR2

What can couse the lag? i would enjoy the game alot if i could play the game with no lag