FPS lag

[maggett]

Hi ive just brought MX simulator for my pc with the specs being

AMD R9 290 4gb

Intel i5 3570k 128gb SSD hard drive

8GB 1600 ram

ASrock z77 extreme motherboard and a 750w PSU

i can run Battlefield 4 on high at 100+ fps but when im trying to play mx simulator i get most of the time 125 fps but some parts round the tracks it just drops to near 100 and just feels unplayable laggy no matter if i use the ultra quality object pack or low

ive got evrything up to date including graphics drivers does anyone have any idea what the problem could be? my brother computer is allmost the same spec and his runs no problem

Thanks