Framedrop rain condition replay

PC, suffering from the same issue. Actually, racing in the rain limits my fps to 30 and instant replay during that limits it to 5. There are also all sorts of visual effects bugs at the rear ends of the cars.

Have you tried looking behind while in the replays? It, for some reason, brings the framerate back to where it was while racing. Keep in mind though, the game will go into a heavy drop as soon as you return to normal view.