I can't get stable Fps on Forza Horizon 3

[96pants]

I'm trying to run Forza Horizon 3 on High but i just can't...

I get stable fps for about 3 or 4 seconds then it spikes down and stabelizes again and it just keeps doing this, except when playing on low graphics. I can't figure out what the reason is and idk if it's ram or not since i can't find anyone with problems because of it.
I get between 100-110 fps and it drops to 10-20...

Specs:

CPU: i7-7700 Quad-Core 3.6GHz

GPU: MSI Radeon RX 580 ARMOR 8G OC

Motherboard: ATX Gigabyte Z270P-D3

HDD: Toshiba P300 1TB

RAM: 1 x G.SKILL Aegis 8GB DDR4-3000MHz CL16

 

[96pants]

Actually i just tried it, it also happens when playing on low graphics, it freezes for a bit and then comes back to normal, it does this a lot i can't even play the game.