SIRRIS F43 MX TUNE FORK FOR SURRON ULTRA BEE
Proven at the highest level. Built from real-world feedback.
F43 MX Tune | Tool Free LSC | 260 mm Travel | Surron Ultra Bee 1.2
MORE TRAVEL. MORE PERFORMANCE.
Now featuring 260mm of travel, tool-free LSC adjustment, Torx fasteners, and updated graphics.
MX Tune is purpose-built for motocross performance. Its race-focused setup delivers the balance, control, and bottoming resistance needed to charge through big jumps, hammer whoops, and attack fast corners at race pace.
RIDER WEIGHT SPECS:
Sirris offers five weight ranges to choose from when selecting your Trail Tune F43 fork. (Listed weight ranges are rider weight without riding gear on. 15 pounds of riding gear is calculated into the weight ranges)
< 160 lbs (Light = 4.4/4.4 springs)
160-200 lbs (Medium = 5.0/4.8 springs)
200-240 lbs (Heavy = 5.4/5.0 springs)
240-280 lbs (X Heavy = 5.4/5.4 springs)
> 280 lbs (XX Heavy = 5.4/5.4 springs)
Fork spring rates listed above are left side/right side.
FORK SPECS:
Architecture
Upside down fork with symmetrical and adjustable pressurized closed cartridge dampers
Travel
260 mm
Free length
856 mm
Fork weight, includes clamps and steerer
22 lbs / 10kg
Stanchions
Ø43, high tensile steel with hard chrome
Outer tubes
Seamless 7050 aluminum, type 3 hard anodized coating
Drop outs
Forged 6061 aluminum, type 3 hard anodized coating
Brake mounting
Sized for stock Ultra Bee calipers and 240mm rotors
Triple clamps
Forged 6061 aluminum, type 3 hard anodized coating
Steer tube
Seamless 7050 aluminum, type 2 anodized coating
Damping
• MX tune
• Symmetrical and adjustable closed cartridge with spring backed IFP
• High-flow pistons and fully tunable compression and rebound valving
• Dual oil circuits for optimum performance. Separate oil circuits deliver optimized damping and lubrication performance.
• Balanced, race-ready, high performance. No matter how hard you ride or how many laps you put in, Sirris closed-cartridge forks deliver consistent, fade-resistant performance and predictable handling lap after lap.
• The hydraulic bump stop system provides progressive bottom-out control, delivering softer landings and maximum usable travel, even under the most aggressive impacts.
Damper bodies
Race-grade internals: Seamless 7050 aluminum, type 3 hard anodized coating providing high durability to keep your ride in top condition.
Spring
Dual side high tensile steel spring, adjustable preload
Adjusters
External tool-free compression, rebound adjustment
(rebound adjusted tooled to ensure durability in the harshest environments)
Seals
NOK Heavy Duty seals
Bushings
Premium Daido bushings (Custom Sirris proprietary design)
Guards
High impact PP, 210-degree wraparound
The new F43 fork receives a significant travel increase for Trail and MX applications, moving from 246mm to 260mm. More usable travel means more capability when the terrain gets aggressive, giving the Ultra Bee greater capacity to absorb hard hits while maintaining control and composure deeper into the stroke. Extended length remains the same.
Across all three tunes—Trail, MX, and SX—the F43 also receives a new tool-free top-cap adjustment system with the signature Sirris blue adjuster, bringing quick, tool-free adjustability directly to the rider. Whether making changes at the track, on the trail, or between sections, suspension adjustments are now faster and easier to access.
Durability and serviceability also get an upgrade with the introduction of Torx fasteners across the F43 platform. The new fasteners provide greater resistance to rounding compared with traditional tool interfaces, delivering a more robust solution for riders, technicians, and professional-level service environments.
Completing the update is an all-new fork guard decal package across Trail, MX, and SX models, giving the F43 a fresh, unmistakably Sirris appearance to match the performance underneath.
TUNING DETAILS & RIDER WEIGHT RANGE
Listed weight ranges are body weight without riding gear (15 pounds of riding gear is calculated into the weight ranges).
Weights of upgrades (battery, controller, etc) need to be added to rider weight.
MX TUNE Starting point notes:
This is the starting point based on feedback from test riders and calculations. Assuming neutral riding position, and 15lbs gear
- Stock bike with 18/21.
- Heavier settings get slightly increasing rear support.
- Riders close to a weight cut off need to adjust preload to compensate
- Weights of upgrades (battery, controller etc) to be added to rider weight with a 2x factor.
- Very aggressive/pro riders to consider +1 weight class and drop preload to get sag. Especially if in the upper range.
- Rider preference and riding conditions may require a different setup.
- Calculations are only valid for stock Ultra Bee swing arm and linkage with stock ratio.
- Relaxed rider = Medium tune with high preload
Example:
- 175lbs rider without gear, 20lbs gear, 20lbs upgrades
- Weight calculation 175+(20-15)+2x20=220
- Neutral rider = Heavy tune
- Aggressive rider = Consider
- X Heavy tune for added support
SETTINGS NOTE: Settings are number of clicks from the closed position (full clockwise). Once they are in the closed position, back them out (counter-clockwise) according to the number of clicks indicated in the chart above to get you to factory settings.
*OIL NOTE: Sirris uses Shell Tellus S2 VX15 (5wt) in the fork cartridge and Shell Tellus S2 VX68 (20wt) as the bath oil. These are cross compatible with other high quality 5wt and 20wt suspension fluids. Sirris uses a semi-synthetic 2.5wt oil in the shock that is also compatible with other high quality 2.5wt aftermarket suspension fluids. You can use 5wt/20wt oils of your preference, Lubefinder.com can be used to source the fork oils. KYB K2C can be used in the shock and has wide availability.
LOWERING KIT
The Sirris lowering kit drops both the front and rear of your Ultra Bee by 28mm vertically, creating a more accessible, confidence-inspiring ride without sacrificing performance.
TECH HELP
Suspension setup, owner's guide, tech help, warranty and more. Learn how to properly set up, use, and maintain your new Sirris suspension products.
