Hi The locomotive DB BR 112 has a BUG as it makes wheel spins all the time in wet weather, even if you activate sand! Thought at first it was only in the scenery Hamburg-Lubeck, but tried the locomotive in another scenery and it was the same problem? Is that something you bother to look at? SINCERELY Brian Scheil
How much power do you apply? Chances are that you need to start slower in rainy conditions and not go full throttle all the time.
In rain I do not apply more than 40-45% power, there was another discussion about this (but sorry, I'm currently too lazy to look it up), give the forums' search function a try