I'm on hard difficulty. First, I tried spa on the mazda rx-vision. I tried RM tires, but couldn't consistently keep up with the leaders who were putting up 2:18's. Also, the opponents only pit once every time, around lap 7 or 8, right around when you can tell if it's going to rain or not. The only way i could at least make up some time was if I used RS tires, where I was putting up 2:16's and got within 4 seconds of the lead before pitting at lap 5 (you can keep racing even if the tires are completely red, but you get a little slower). The only way I could win using the mazda was if the track stayed dry enough where I can go back to the RS tires (i only raced 1 race where it was dry the entire way, but i crashed cuz im an idiot). I couldn't make up time on the intermediate/wet tires.
I ended up switching to the BRZ, which wasn't fastest on the straights, but a lot more stable and faster out of corners. Plus, it didn't burn thru your tires as fast as the mazda. So all I had to do was just put out good laps and I would eventually take the lead. BUT, for my first/only race on the BRZ, I lucked out because it rained super hard early in the race and I pitted for wet tires while everybody spun out. I won by 13 seconds in the end.
Just wanted to post this for anybody else struggling, cuz i thought this was gonna be easy but it wasnt for me lol (just a casual player)