For the 2014–2016 KTM RC390, the YSS Z1 Open Cartridge Kit (Part Number: CO208-680TRC-02) is a professional-grade suspension upgrade designed to replace the non-adjustable stock fork internals with a fully adjustable racing system.
Key Features & Specs
This "Open" design is FIM homologated, meaning it is legal for competition in series like World Supersport 300, but it is equally effective for improving street handling.
Full Adjustability: Provides independent control over Compression, Rebound, and Threaded Spring Preload.
Internal Hardware: Equipped with a 20mm piston and an 8mm shaft for precise damping.
Spring Options: Kits typically come with 260mm springs. You can find "Medium" setups with 8.0 N/mm springs or "Harder" variants (9.0 N/mm) depending on your weight and track requirements.
Maintenance Info: YSS recommends using R5W fork fluid with an oil height set at 170mm.