Diaz Suspension Design

Lower Runt RS - Zeb

Diaz Suspension Design Lower Runt RS is a tuning-focused air spring upgrade designed specifically for the RockShox ZEB equipped with the Gold ButterCup air spring. By adding adjustable preload and expanded negative-spring control, it targets common air-fork complaints—soft “dead spot” at the start of travel and overly progressive ramp—while keeping the packaging and adjustability advantages of an air system.

This patented lower assembly can be run on its own or paired with the Upper Runt for a broader range of spring-curve tuning, especially for riders who want a more coil-like initial feel without giving up the ability to fine-tune spring rate and end-stroke behavior.

Tuning advantages for ZEB riders

• Compatibility - Only fits RockShox ZEB forks with the Gold ButterCup air spring
• Adjustable preload (shim-tuned) - Shims placed above the negative coil spring add positive preload to firm up the first part of travel and reduce the mushy off-the-top feel
• Coil-like support with air-spring flexibility - Preload adjustment mimics the supportive start of a coil while retaining air’s tunability, including effectively “infinite” spring-rate options via air pressure changes
• Adjustable negative air volume - Expands negative-spring tuning range for more control over initial feel and breakaway without relying on compromises elsewhere in the system
• Reduced progression in the lowers - Floating negative piston helps limit pressure build-up and vacuum forces in the lower legs, reducing unwanted ramp and improving progression control
• Designed to work with the Upper Runt - Reduced progression in the lowers creates more room to fine-tune overall progression when combined with the Upper Runt