Sirris F43 FORK FOR ZERO XB
F43 CMX Tune | Tool Free LSC | 220 mm Travel | Zero XB
Sirris offers one weight range for the CMX F43 fork for Zero XB. (Listed weight range is rider weight without riding gear on. 15 pounds of riding gear is calculated into the weight ranges)
160 lbs - 180 lbs (Medium = 3.6/3.2 springs)
Fork spring rates listed above are left side/right side.
FORK SPECS:
Architecture
Upside down fork
Travel
220 mm
Free length
775 mm
Fork Spacing
178 mm - allows for unlimited tire choice
Fork weight
4 kg per leg (driven by sturdy construction required for the forces and speeds encountered when pushing these bikes to their limits without compromising performance)
Stanchions
Ø43, high tensile steel with hard chrome
Outer tubes
Seamless 7050 aluminum, type 3 hard anodized coating
Drop outs
6061 aluminum, type 2 anodized coating
Replaceable caliper mount brackets allow for caliper and wheel upgrades
Brake mounting
• Sized for 220mm rotors, replaceable caliper mount brackets allow for caliper and wheel upgrades
• Zero XB 220mm rotor brake bracket is included
Axle
Ultra-high tensile hard chromed axle increases steering precision and confidence
Triple clamps
Billet 6061 aluminum, type 2 anodized coating, black
Steer tube
Seamless 7050 aluminum, type 2 anodized coating
Stem mount
Designed for use with stock Zero Stem
(4-Bolt direct mount stem will not work with Zero dash mounts)
Top cap system
Motorcycle-style top cap allows for more consistent control over steering bearing tension
Damping
• CMX tune (Compact Motocross Tune)
• Symmetrical and adjustable closed cartridge with spring backed modified IFP
• High-flow pistons + fully tunable compression and rebound valving
• Dual oil circuits for optimum performance. Separating lubrication and damping oils allows us to further optimize high and low speed damping performance.
• Balanced load, race-ready, high performance. No matter how hard you ride or how many laps you take, our closed cartridge forks will never fade and will always feel predictable.
• Hydraulic bump stop is a hydraulic bottom out control system that gives you soft landings and max stroke even on the most aggressive impacts.
Damper bodies
Seamless 7050 aluminum, type 3 hard anodized coating providing high durability and scratch resistance to keep your ride in top condition.
Rebound
Dual side high tensile steel spring, adjustable
Adjusters
External tool-free compression, rebound adjustment
(rebound adjusted using tool)
Seals
NOK MX seals
Bushings
Daido MX bushings
Guards
High impact PP, 210-degree wraparound
Engineered by Sirris.
Tuned by Zero.
The Sirris F43 CMX fork for the Zero XB combines a race-built F43 chassis with a symmetrical closed-cartridge damper system and two independent sealed dampers. With wide-range XB-specific tuning, adjustable compression and rebound, and direct-fit integration, it delivers sharp handling, confident control, and elevated front-end performance for real trail riding.
OVERSIZED TO OUTPERFORM
We took the race-proven F43 chassis — the gold standard in high-performance e-moto suspension — and resized and lightened it for compact e-moto. The result is a fork that rides like it belongs on a full-size race bike.
- Oversized 43mm stanchions, 7XXX-series hard-anodized uppers, and 775mm extended length deliver a longer, stiffer, more planted front end
- 220mm of terrain-devouring travel
- Lightweight billet clamps (double bolt upper and lower) provide stiffness and resist twisting
- Wider 178mm fork spacing for unlimited tire choice
- Direct mount stem compatibility
- Replaceable brake caliper adapters and swappable wheel spacers for cross-compatibility with future bikes
- Custom ultra-stiff, race-grade chromoly axle maximizes control, steering precision, and predictability
- Motorcycle-style top cap allows for more consistent control over steering bearing tension
- 43mm hard chrome stanchions resist flex, dents, and nicks
- 7XXX-series hard-anodized uppers for maximum strength and durability
The Partnership
Sirris Suspension — Engineering & Manufacturing
Sirris designed and produced the suspension hardware used in this system. That includes:
- The fork platform
- Internal architecture and component design
- Manufacturing, assembly, and quality control
Sirris’ responsibility is the suspension units themselves—their engineering integrity, structural performance, and build quality.
Zero Motorcycles — Tune Development & Installation Integration
Zero Motorcycles led the development of the ride character and integration for the XB model.
That includes:
- Defining ride goals for the XB platform
- Developing the wide-range tune
- Testing across varied terrain conditions
- Validating fitment and chassis compatibility
- Establishing installation procedures
This suspension system was tuned specifically for the Zero XB as a complete vehicle—not just as individual components.
Unlike a custom race conversion, this setup was engineered as a direct bolt-on replacement for the stock suspension.
For that reason, Zero Motorcycles owns the vehicle-side tuning philosophy and installation guidance for this application.
Why Tune & Fitment Are Owned by Zero Motorcycles
Suspension performance is not just about hardware—it’s about how that hardware interacts with the motorcycle’s geometry, weight balance, and intended use. For the XB platform:
- Zero defined the wide-range valving
- Zero validated spring rates for general-use riding
- Zero confirmed geometry compatibility
- Zero established installation procedures
Sirris manufactures the suspension units to Zero’s specification. However:
- Sirris does not control the motorcycle chassis
- Sirris does not define vehicle geometry targets
- Sirris does not publish vehicle-specific setup instructions
Because this is a vehicle-integrated application, all XB-specific tuning intent, setup recommendations, and installation instructions are developed and supported by Zero Motorcycles.
If you have questions regarding bike setup, torque specifications, ride modes, or compatibility with other XB components, please contact Zero Motorcycles directly.
Responsibility & Authenticity
We’re proud of this collaboration—and clarity matters.
- Sirris stands behind the engineering and manufacturing of the fork.
- Zero Motorcycles stands behind the vehicle integration, tuning specification, and installation guidance for the XB application.
Both teams share a commitment to thoughtful engineering and rider-focused innovation.
Because this system installs as a direct replacement for the stock suspension, proper installation according to Zero Motorcycles’ published procedures is essential to ensure safety and performance.
ZERO XB OWNER'S GUIDE
Sirris F43 fork for Zero XB - torque specs, tuning charts and more.
SERVICE PARTS
F43 Zero XB fork service parts available now.
