EXT REA MX vs. Sirris R46 Rear Shock for the Surron Ultra Bee: Specs, Weight, and Feel

The Surron Ultra Bee left the factory with more chassis capability than its rear shock knows what to do with. The OEM unit is fine for cruising, but the moment you start jumping, braking hard into ruts, or carrying real speed through chop, it blows through its travel, packs down, and leaves the back end skittering. Two aftermarket shocks dominate the Ultra Bee upgrade conversation: the EXT REA MX and the Sirris R46. Both are purpose-built for the Ultra Bee's linkage rear end, both are fully tunable, and both completely change how the bike rides. This guide breaks down the specs, weight, adjustability, and fitment so you can pick the right one for how you ride.

Why the Rear Shock Is the Ultra Bee's Highest-Impact Suspension Upgrade

The Ultra Bee runs a linkage-driven rear end, which means the shock is doing real motocross work — it has to control a rising-rate curve, not just soak up bumps. The stock damper has limited low-speed control and a rebound circuit that can't keep up once you add rider weight, controller amps, and bigger hits. The result is a bike that feels planted in the driveway and vague on the trail. A proper coil-over shock with independent compression and rebound tuning fixes the two things that matter most: it holds the bike up in its stroke so you don't bottom on landings, and it controls how fast the wheel returns so the rear tire stays hooked up instead of bouncing. Because the rear shock affects traction, geometry, and bottoming resistance all at once, it delivers more usable change per dollar than almost any other bolt-on you can make to an Ultra Bee.

Sirris R46: Specs and Ride Character

The Sirris R46 was engineered specifically around the Surron Ultra Bee, and the fit shows. It runs a high-flow 46mm billet-aluminum piston in a 320mm x 85mm-stroke body and comes in at just 3.9 lbs (1.76 kg) without the spring — genuinely light for a fully-adjustable coil shock. It's a piggyback design with a pressurized, floating-piston reservoir and a 16mm hollow chrome-plated, induction-hardened shaft, all wrapped in a Type 3 hard-anodized body that still looks new after thousands of miles. Tuning is handled through low-speed compression and rebound adjusters, with high-tensile steel spring rates matched to riders up to 300 lbs. On the trail the R46 feels supple off the top — small-bump compliance is excellent — while the reservoir keeps damping consistent on long descents. It's the shock for riders who want a plush, planted, Ultra Bee-specific setup with a lighter package.

EXT REA MX: Specs and Ride Character

The EXT REA MX comes from a race-suspension house with real enduro and motocross pedigree, and every shock is pre-tuned by EXT-USA to the weight and riding style you provide at order time. It's a direct bolt-on for the Ultra Bee built around a robust 40mm damper body and a 16mm shaft, with 4-way adjustability: low- and high-speed compression, low-speed rebound, and EXT's Hydraulic Bottom-Out Control (HBC). The HBC circuit is the headline feature — it lets you run a softer main spring for plush small-bump feel while adding progressive damping support through the last 15% of the stroke, so you get comfort and bottoming resistance at the same time. Add very low reservoir pressure for sensitivity, low hysteresis for quick response, spherical-bearing mounting hardware, and an EXT superlight V2 spring (450–600 lb options), and you have a shock that feels like a race machine. It's the pick for riders who push hard and want a factory-valved setup dialed to their spec.

Head-to-Head: Spec Comparison

Fitment and Install Notes

Both shocks are a direct bolt-on for the OEM Ultra Bee unit — no extra hardware required — but there are two things worth knowing before you wrench. First, spring clearance: Sirris designs the R46 to run the largest possible piston within the stock linkage, and tolerances vary bike to bike, so they strongly recommend running their higher-clearance rear triangle to prevent spring-to-triangle contact. The EXT REA ships with motorsport spherical-bearing mounting hardware and bolts in directly. Second, spring rate: order the rate that matches your kitted weight (rider plus gear), not your bare bodyweight — an Ultra Bee rider in full kit is often 15–20 lbs heavier than they guess, and an undersprung shock wallows no matter how good the damping is.

Install itself is straightforward with the bike on a stand and the rear wheel supported: pull the lower shock bolt, then the upper, swap in the new shock, and torque both mounting bolts to roughly 40–45 Nm (always confirm against your service manual). Set sag first — aim for about 30% of rear travel with you on the bike in gear — then dial compression and rebound a few clicks at a time. Small changes make a big difference on a bike this light.

Which One Should You Run?

If you want the lightest, most plush, Ultra Bee-specific setup with excellent small-bump traction, the Sirris R46 is the pick — just plan on the clearance triangle for a clean install. If you ride aggressively, session long rough trails or MX tracks where bottoming resistance and heat matter, and you want a factory-valved shock pre-tuned to your exact weight and style, the EXT REA MX and its HBC bottom-out control are the stronger tool. Neither is a wrong answer — both are a night-and-day upgrade over stock. The real mistake is leaving the OEM shock on a bike that's capable of so much more.

Ready to fix the back of your Ultra Bee? Browse the full lineup of rear shocks and linkage parts in the ThrottleCo Shocks collection and the broader Suspension collection at throttleco.store — rider-vetted, spec'd for your platform, and shipped fast from the USA.