EXT REA MX vs. Sirris R46: Best Rear Shock for the Surron Ultra Bee (2025 Spec Guide)
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The Surron Ultra Bee is a serious machine. Factory suspension? Not always up to the task once you start pushing it. Whether you're hitting trails, tracks, or big jumps, a quality rear shock is one of the highest-impact upgrades you can make. Two names keep coming up in the Ultra Bee community: the EXT REA MX and the Sirris R46. Here's exactly how they stack up — no fluff, just specs and real talk.
The Surron Ultra Bee Has a Rear Shock Problem
Out of the box, the Ultra Bee's rear suspension is functional but not dialed. The stock shock lacks the adjustability serious riders need, and the spring rate is a compromise that doesn't favor anyone at the extremes. Heavier riders bottom out. Lighter, faster riders find it vague. The good news: the mounting dimensions are friendly to aftermarket shocks, and the community has done the legwork on what fits and what doesn't.
The two shocks that consistently rise to the top are the EXT REA MX (Italian-made, motorsport pedigree) and the Sirris R46 (engineered specifically for the e-moto segment). Both are bolt-on for the Ultra Bee. Both are a massive step up. The question is which one matches your riding style and budget.
The Contenders
EXT REA MX
EXT Racing is an Italian suspension company with deep roots in enduro and motocross. The REA MX is their purpose-built rear shock for the high-performance e-moto and MX market. It features a piggyback reservoir, fully adjustable compression and rebound, and custom valving options for rider weight and terrain. EXT has been producing race-spec suspension for over a decade — this isn't a rebranded generic shock.
Sirris R46
Sirris entered the scene with a laser focus on electric off-road bikes. The R46 was designed from the ground up with the weight and torque characteristics of e-motos in mind. It uses a larger-bore piston than most shocks in this price range, which gives it a more linear feel under high-speed impacts. Custom spring options and valving are available direct from Sirris for rider-specific setups.
Head-to-Head Spec Breakdown
| Spec | EXT REA MX | Sirris R46 |
|---|---|---|
| Piston Size | 46mm | 46mm |
| Shaft Diameter | 16mm | 16mm |
| Eye-to-Eye Length | 320mm | 320mm |
| Stroke | 65mm | 85mm |
| Reservoir | Piggyback | Piggyback |
| Compression Adjust | LSC + HSC | LSC |
| Rebound Adjust | Yes (LSR + HBC) | Yes |
| Custom Valving | Yes (rider-specific) | Yes (rider-specific) |
| Spring Options | 450–600 lb | Up to 300 lb rider |
| Fits Stock Triangle? | Yes | Recommended upgrade |
On paper they're comparable in piston and shaft spec — the differences show up in the ride feel, adjustability range, and in the details of how each brand approaches valving and service.
Installation: What to Know Before You Order
Both shocks are direct fits for the Surron Ultra Bee's rear linkage. No fabrication required. Before you order, confirm your eye-to-eye measurement and stroke spec with the seller — early Ultra Bee frames and newer production runs can have slight dimensional differences. Both EXT and Sirris offer Ultra Bee-specific listings, so check that when adding to cart.
One note on the Sirris R46: Sirris recommends using their upgraded triangle for guaranteed fitment, as the R46's larger piston diameter can have light contact with the stock linkage depending on frame tolerances. The EXT REA MX bolts directly to the stock triangle with no clearance issues.
Installation is a two-person job or a quality bike stand job. Remove the rear subframe bolts, drop the linkage, swap the shock, reassemble. Budget about 45 minutes your first time. Set sag before your first ride — target 30–35% of total travel for trail riding, 28–32% for track.
Ride Feel: Which Shock Matches Your Style?
EXT REA MX — Precise and Planted
The EXT REA MX rewards riders who want feedback. It's not soft — it's controlled. Mid-stroke support is excellent for square-edge hits at speed. The high-speed compression circuit is notably well-tuned from the factory; most riders run it close to stock HSC and adjust LSC to taste. The HBC (Hydraulic Bottom-Out Control) is a standout feature — it lets you run a softer spring rate without sacrificing end-stroke support. If you're an aggressive trail rider or doing moto-style laps on a track, the REA MX is in its element. Experienced riders will love it.
Sirris R46 — Supple and Forgiving
The Sirris R46 is tuned with a more forgiving character out of the box. The initial stroke is plush, which makes slow-speed technical sections feel confidence-inspiring. Under hard acceleration (and the Ultra Bee has plenty), the R46 holds composure well without the kick-up you get from cheaper shocks. The 46mm piston delivers a notably linear feel through the mid-stroke. If you're newer to tuned suspension or do a mix of trail and casual riding, the R46's more accessible feel works in your favor.
Which One Should You Choose?
Go EXT REA MX if: you're an experienced rider who wants maximum adjustability and feedback, you ride at speed on varied terrain, or you have specific valving requirements based on your weight and riding style.
Go Sirris R46 if: you want a high-performance shock with a more forgiving out-of-the-box setup, you're newer to aftermarket suspension, or you ride a mix of aggressive and casual terrain.
Both are massive upgrades from stock. Either one you choose, you'll feel the difference on the first ride. In stock and ready to ship from the USA.
What About LBX, Talaria, and E-Ride Pro Riders?
If you're riding an LBX, Talaria Sting, or E-Ride Pro rather than the Ultra Bee, the EXT lineup has you covered too. The EXT Arma MX is the rear shock spec'd for those platforms — same premium EXT internals, different eye-to-eye length tuned for those frames. Fitment varies by bike — reach out before ordering if you're not on the Ultra Bee platform and we'll help confirm compatibility.
Frequently Asked Questions
Does the EXT REA MX fit the Surron Ultra Bee without modification?
Yes. The REA MX is available in an Ultra Bee-specific configuration with the correct eye-to-eye length and stroke. No frame modification required. Confirm the spec with us before ordering if you're unsure of your frame generation.
What spring rate should I order for the Sirris R46?
Spring rate depends on rider weight and riding style. As a baseline: under 160 lbs go softer, 160–200 lbs use the standard rate, over 200 lbs go stiffer. Sirris specs the spring to your setup at checkout — options cover riders up to 300 lbs.
Can I service these shocks myself?
Basic service (oil change, seal replacement) is doable at home with the right tools. Full revalving is best left to a qualified suspension tech or sent back to the manufacturer. EXT has service centers in North America; Sirris services can be arranged through the dealer network.
How much does a rear shock upgrade improve the Ultra Bee's performance?
Significantly. Most riders report the rear shock is the single highest-impact suspension upgrade on the Ultra Bee. Better chassis control under acceleration, reduced fatigue on technical terrain, and more confidence in the air all follow from a quality shock swap.
Do you offer custom valving when I order?
Yes. When you order an EXT REA MX or Sirris R46 through ThrottleCo, provide your rider weight, riding style (trail, track, mixed), and any specific setup notes. We'll pass that to the manufacturer for rider-matched valving before it ships.