Make sure you are not using time trial mode, in TT the cars have no fuel weight and no tire wear, both will make your car much faster. I always set up a race lobby and save the settings on my PS4 so I can practice under real race conditions. You can also go to the arcade tab and set up a "custom race" and use the same tire wear, fuel use settings, time of day, slip stream settings, and grip settings that Coldwarrior uses for the race. You can also select opponent strength, penalties, track boundary penalties, laps, starting position, and flag rules. Once again, never, ever, under any circumstance use Time Trial, unrealistic weight, no tire wear, and too much grip. I believe that in TT wet races have the same grip as dry races, the rain is nothing more than a visual setting.