Version 1.45 was the build optimized for this content. Consequently, this version contains specific map assets and engine optimizations related to the western Russian terrain that were polished to a high degree. For players seeking to experience the game in its most complete geographic form (often via unofficial means or beta archives), 1.45 represents the "lost" era of the game where this content was ready for deployment.
If you are using the legacy version of the game (bought directly from the developer rather than Steam), you can use the official : download euro truck simulator 2 version 145 best