Sirris F43 CMX 220mm Tool-Free LSC Fork | By Sirris Suspension | For Zero XB

Built to Dominate Any Terrain, Any Time

At REV Rides we see a lot of riders pushing the Zero XB harder than its stock suspension was ever designed for. The Sirris F43 CMX Fork is one of the most serious upgrades you can install if you want to unlock the true performance potential of this platform. This fork brings full-size motocross suspension engineering to compact electric bikes, giving riders a front end that feels stronger, more precise, and far more capable in aggressive riding conditions.

The F43 CMX combines an oversized 43mm upside-down race chassis with Sirris’ proprietary CMX tuned closed cartridge damping system. The result is razor sharp handling, incredible front-end confidence, and a suspension platform that stays consistent even when speeds pick up and terrain gets rough. With 220mm of travel, tool-free compression adjustment, and race-grade materials throughout the fork, this upgrade dramatically improves the ride quality and control of the Zero XB.

Sirris built the F43 platform by taking their race-proven fork architecture and resizing it for compact e-moto bikes. The 775mm extended chassis, oversized stanchions, and billet clamps create a longer, stiffer, and more planted front end while still keeping the bike responsive. The entire design focuses on reducing flex, improving durability, and delivering predictable performance when riders push these bikes harder on trails, jumps, and technical terrain.

Oversized Chassis Designed to Outperform

• 43mm hard chrome stanchions resist flex, dents, and wear

• 7XXX series hard anodized uppers maximize strength and durability

• 775mm extended fork length creates a longer and more planted front end

• 220mm travel delivers 20mm more suspension travel than many stock compact e-moto forks

• Lightweight billet aluminum clamps increase stiffness and reduce twisting under load

• 178mm fork spacing allows nearly unlimited tire choices for dirt or street setups

• Direct mount stem compatibility improves cockpit stiffness and steering feel

• Custom ultra stiff chromoly axle improves steering precision and predictability

• Motorcycle style top cap system provides more consistent steering bearing tension

• Replaceable brake caliper adapters and wheel spacers allow brake and wheel upgrades

The result is a fork that is not just stiffer. It is stronger where it matters, absorbs impacts better, and maintains consistent performance during long aggressive rides.

Race Grade CMX Closed Cartridge Damping

At the heart of the F43 CMX is Sirris’ CMX tuned symmetrical closed cartridge damper. This advanced system delivers professional level damping performance using independent oil circuits that separate lubrication and damping oil. This design keeps the fork running cool and consistent even when riding hard for extended sessions.

• CMX Compact Motocross Tune designed for aggressive compact e-moto riding

• True symmetrical closed cartridge system provides fade-free damping

• Independent oil circuits separate lubrication and damping oil

• High flow pistons with tunable compression and rebound valving

• Hydraulic bottom-out control protects against harsh impacts

• Hard anodized internal components reduce wear and extend service life

• Premium Daido bushings and NOK MX seals deliver smooth action and durability

CMX tuning gives the Zero XB a planted, predictable ride feel that riders notice immediately. Whether riding technical trails or pushing faster off-road sections, the fork stays controlled and highly tunable.

Tool-Free Compression Adjustment

The F43 CMX features tool-free compression adjusters, allowing quick suspension tuning without tools. Riders get nearly 30 clicks of external compression adjustment, making it easy to adapt the fork to different terrain or riding styles.

Direct Mount Stem System

The Sirris steerer tube and motorcycle-style top cap system are designed around a direct mount stem setup. This improves cockpit stiffness and helps maintain consistent steering bearing torque similar to larger motocross bikes.

Optional Drop Clamp for Big Wheel Builds

The optional drop clamp raises the front end an additional 25mm, extending overall fork length to approximately 800mm. This allows riders to run a 21 inch front wheel while maintaining bike balance when paired with a longer rear suspension setup.

Axle and Brake Mount System

• Ultra stiff chromoly axle improves steering precision and front-end feel

• Replaceable caliper mount brackets allow brake upgrades

• Designed for 220mm brake rotor setups

• All Sirris brake brackets are designed for 220mm rotors

Technical Specifications

• Architecture: Upside down fork

• Travel: 220 mm

• Free Length: 775 mm

• Extended Length with Drop Clamp: Approximately 800 mm

• Fork Spacing: 178 mm

• Weight: 4 kg per leg

• Stanchions: Ø43 mm high tensile steel, hard chrome

• Outer Tubes: Seamless 7050 aluminum, Type 3 hard anodized coating

• Drop Outs: 6061 aluminum, Type 2 anodized coating

• Axle: Ultra high tensile hard chromed axle

• Triple Clamps: Billet 6061 aluminum, Type 2 anodized coating, Black or Blue

• Steer Tube: Seamless 7050 aluminum, Type 2 anodized coating

• Damping: Symmetrical adjustable closed cartridge with spring backed modified IFP

• Damper Bodies: Seamless 7050 aluminum, Type 3 hard anodized coating

• Compression Adjustment: External tool-free compression adjuster

• Rebound: Dual side high tensile steel spring, adjustable (rebound adjusted using tool)

• Seals: NOK MX seals

• Bushings: Daido MX bushings

• Fork Guards: High impact PP, 210-degree wraparound

Spring Rate Options

• Medium: 140 to 180 lb rider weight, 3.6 / 3.2 springs

• Heavy: 180 to 220 lb rider weight, 3.6 / 3.6 springs

Rider weight ranges are based on body weight without riding gear. Sirris factors approximately 15 pounds of riding gear into the recommended ranges. Any heavier upgrades such as batteries or controllers should be added to rider weight when selecting spring rates.

CMX Tune Setup Notes

• Factory settings are measured in clicks from the fully closed position

• Once closed fully clockwise, back adjusters out counter-clockwise to reach the recommended starting settings

• Riders near a weight cutoff may adjust preload to fine tune sag

• Aggressive riders may benefit from moving up one spring class and lowering preload

• Rider preference and terrain conditions may require further tuning

• Example: a 160 lb rider with 20 lb of upgrades calculates to 180 lb total system weight

• Aggressive rider at 180 lb may prefer the heavy tune with lower preload

• Relaxed rider at 180 lb may run the medium tune with higher preload

Fitment

• Zero XB

Who This Fork Is Perfect For

• Zero XB riders building a high performance off-road setup

• Trail riders who want better front-end stability and durability

• Upgraded builds that need true motocross level suspension performance

Fitment: Sirris F43 CMX 220mm Fork | Tool free LSC | Zero XB

• Zero XB

This product may be compatible with more models than shown above. Please see the product description for full details, or contact us for help with fitment.