Sirris F43 CMX 220mm Tool-Free LSC Fork | Altis Sigma

Built to Push the Altis Sigma Further

At REV Rides we see riders pushing the Altis Sigma well beyond what the stock suspension was originally designed for. Once you start adding power upgrades, riding rough terrain harder, hitting larger jumps, or building a dedicated off-road machine, suspension quickly becomes one of the most noticeable limitations. The Sirris F43 CMX was designed for riders who want true motocross-level front suspension performance on their compact e-moto setup.

The F43 CMX combines an oversized 43mm upside-down race chassis with Sirris' proprietary CMX tuned closed cartridge damping system. The result is a front end that feels stronger, more planted, and more precise when speeds increase and terrain gets rough.

For riders building serious Altis Sigma setups, the improvement is immediate. You gain better steering precision, reduced chassis flex, improved impact absorption, and a more predictable feel through rough sections.

Important Altis Sigma Fitment Notes

This is a special order item and requires contacting the REV Rides team before purchase to get you this set up just for you. This setup requires modifications and is intended for riders building more aggressive Altis Sigma setups. Please review all installation notes before ordering.

• Special order item currently only, contact REVRides.com/contact before purchasing
• Requires drilling and tapping of certain things
• Requires modification of dust seals
• Requires a different handlebar clamp setup
• Requires a different headlight mount
• Creates a noticeably stiffer overall front-end setup compared to stock
• Recommended for experienced builders or riders performing larger custom builds we suggest a professional to do these modifications 

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 more planted front end
• 220mm travel delivers additional suspension capability over many stock compact e-moto forks
• Lightweight billet aluminum clamps reduce twisting under load
• 178mm fork spacing opens tire options for dirt and street setups
• Direct mount stem compatibility improves steering feel and cockpit rigidity
• Ultra-stiff chromoly axle increases front-end precision
• Motorcycle-style top cap system improves steering bearing consistency
• Replaceable brake adapters and wheel spacers allow future wheel and brake upgrades

This is not simply a stiffer fork. It is designed to be stronger where it matters, absorb impacts more effectively, and maintain predictable handling during aggressive riding.

Race Grade CMX Closed Cartridge Damping

At the heart of the F43 CMX is Sirris' CMX tuned symmetrical closed cartridge damping system. This advanced design separates lubrication oil from damping oil, helping maintain consistent performance under heavy use and extended riding sessions.

• CMX Compact Motocross Tune developed for aggressive compact e-moto riding
• True symmetrical closed cartridge design
• Independent oil circuits for fade resistance
• High-flow pistons with tunable compression and rebound valving
• Hydraulic bottom-out protection
• Hard anodized internal components reduce wear
• Premium Daido bushings
• NOK MX seals for smooth action and durability

Whether riding rough trails, technical terrain, desert sections, or larger jump lines, the F43 CMX remains controlled and highly tunable.

Tool-Free Compression Adjustment

The F43 CMX features external tool-free compression adjustment with nearly 30 clicks of adjustment. Riders can quickly adapt suspension settings for changing terrain or riding style without carrying tools.

Direct Mount Stem System

The Sirris steerer tube and motorcycle-style top cap system were designed around direct mount stem setups. This creates a stiffer cockpit feel while helping maintain consistent steering bearing tension similar to larger motocross platforms.

Optional Drop Clamp for Big Wheel Builds

The optional drop clamp raises overall fork height approximately 25mm, extending total fork length to roughly 800mm. This helps riders running larger wheel setups maintain proper geometry and bike balance.

Axle and Brake Mount System

• Ultra-stiff chromoly axle improves steering precision
• Replaceable brake brackets allow future brake upgrades
• Designed for 220mm brake rotor setups
• Sirris brake brackets designed around 220mm rotors

Technical Specifications

• Architecture: Upside down fork
• Travel: 220mm
• Free Length: 775mm
• Extended Length with Drop Clamp: Approximately 800mm
• Fork Spacing: 178mm
• Weight: 4kg per leg
• Stanchions: Ø43mm 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 adjuster
• Rebound: Adjustable dual-side high tensile spring system
• Seals: NOK MX seals
• Bushings: Daido MX bushings
• Fork Guards: High impact PP, 210-degree wraparound

Spring Rate Options

• Medium: 140-180 lb rider weight, 3.6 / 3.2 springs
• Heavy: 180-220 lb rider weight, 3.6 / 3.6 springs

Rider weight recommendations are based on body weight without riding gear. Sirris factors approximately 15 pounds of riding gear into these recommendations. Additional battery, controller, or accessory upgrades should be added into total rider system weight.

CMX Tune Setup Notes

• Factory settings are measured in clicks from fully closed position
• Fully close adjusters clockwise, then back out counter-clockwise to recommended starting settings
• Riders near spring weight cutoffs can fine tune with preload adjustments
• Aggressive riders may prefer moving up one spring class with reduced preload
• Terrain and rider preference may require additional tuning
• Example: 160 lb rider with 20 lb of upgrades equals 180 lb total system weight

Fitment

• Altis Sigma

Who This Fork Is Perfect For

• Altis Sigma riders building high-performance off-road setups
• Trail and desert riders wanting increased front-end stability
• Jump riders and aggressive riders pushing beyond stock suspension limits