High-speed gearboxes are required to keep the engine from redlining. These mods often introduce specialized transmissions with longer gear ratios designed for top-end speed rather than heavy towing.
usually requires combining a "No Speed Limit" modification with a custom "Engine/Transmission" mod. While the base game and most standard "Fast" mods reach about 260 km/h, achieving 400 km/h while maintaining "extra quality" (realistic handling and sound) is a specialized niche. Steam Community Recommended Mod Setup for 400 km/h+ euro truck simulator 2 speed mod 400 km h extra quality