v1.40 introduced a completely new lighting system (physically based lighting), reworked sound, and new roads. v1.39 is considered lighter on hardware and more mod-compatible.
Choosing a legitimate copy ensures you have a safe, stable experience with full access to the Steam Workshop and official multiplayer features. for version 1.39 or how to install official mods
: Introduced a "Turbo Slider" to let you fine-tune the cabin's turbo whistle, alongside improved spatial mixing for more realistic cockpit sounds. New AI Vehicles