When I run Rfactor 2, it usually runs fine with getting around 100 to 300 fps on most tracks, but there are many ocassions where running at exactly the same settings and track/car combo the game is barely running at 30 fps. I tried different settings but the result is the same.
Probably rF2 'lost focus'. Try alt-tabbing to something else, then back to rF2. PS Are you sure you get 100-300 fps with a GTX 750?
On low settings and 1 car yes, but on old isi tracks I can get high fps even with medium to high settings and car around
I assume that's a GPU with 2 GB VRAM (even 1GB GTX 750 exists). In any case, both with 1 and 2 GB VRAM, you will run into issues where performance drops when you go above VRAM limit of your card. For example Sebring with default settings and a grid of 20 cars will consume about 3 GB. The only solution for this problem is to drop texture and opponent details or run races with less cars.