Its not just you, It kinda evens out later on Mine absolutly Hated the rain and when your Racing in the R 121-160 it is Ridiculus. But on the other hand when the weather goes your way you are so much faster.

There are also weather Patterns where it will start with rain then go into sunshine then to rain again to sunshine pick your moments when to sprint when to ease up a bit cause you should be able to catch up. the weather makes it more interesting especially when you get a handle on his stamina during rain you will be invincible on sunny days