SIGEYI AXO SL Spider Power Meter: Sprint-Cadence Bug, Skip

The SIGEYI AXO SL is the second-generation successor to the SIGEYI AX315, a 110 BCD 4-bolt spider power meter that we had previously tested and found to be a competent device (only a 3% trim was needed in the test data). The AXO SL is marketed on weight and stiffness improvements: the manufacturer claims 79g, and we measured 77g. The price is $376 USD for the spider alone (not including the crank or chainrings), positioning the AXO SL in the budget-spider segment between the Magene P505 ($299) and the high-end Quarq DZero ($1,099). The headline specs are ±1% accuracy, 2000W max power, 220 RPM max cadence, L/R balance (estimated), cadence smoothness, IP67 sealing, ATC automatic temperature compensation, 300h rechargeable battery with magnetic USB charging, ANT+ and Bluetooth dual protocol, and oval chainring support.

Our test of the AXO SL was cut short on the first ride. The test protocol is the standard JoyVelo indoor + outdoor validation: warm-up, 200W steady-state baseline, repeated >1000W sprints, return to 200W, repeat. The indoor test on the Tacx Neo 3M reproduced a sprint-cadence-sensor failure on the first session: the cadence sensor dropped to zero under >1000W load, and the power calculation (torque × cadence) followed the cadence to a reported value of 100-200W on a 1200W sprint. The outdoor first ride reproduced the same failure on every hard effort: a sprint, a threshold effort, or a steep hill climb would cause the cadence sensor to either drop to zero or briefly report a falling cadence before climbing. The L/R balance data was also wildly random — an algorithm bug that the manufacturer documentation acknowledges. The test was paused and the data was sent to SIGEYI; the vendor has not committed to a fix as of the time of writing.

The fundamental problem with the AXO SL is a hardware-level cadence-sensor failure under high-torque load. The same failure mode plagued the early Garmin Rally 200 and Vector 3 pedal PMs, and Garmin could only resolve it in hardware with the Rally X100 series (which added a hardware gyroscope to maintain cadence data during the sensor dropout). A firmware fix is unlikely because the failure is in the cadence sensor itself, not in the firmware interpretation of the sensor data. The previous-generation SIGEYI AX315 did not have this issue; the AXO SL is a regression.

TL;DR

The SIGEYI AXO SL is a 77g 110 BCD spider power meter that, on the first ride, reproduced a sprint-cadence-sensor failure that renders the power data unusable under hard acceleration. The cadence sensor drops to zero (or briefly reports a falling cadence) under >1000W load, and the power calculation follows it to garbage. The same failure mode plagued the early Garmin Rally 200 and Vector 3 pedal PMs, which Garmin could only fix in hardware with the Rally X100 series. The L/R balance algorithm is broken in the current firmware, producing wildly random data. The steady-state power data drifts 5-10W between rides on the same trainer. The previous-generation SIGEYI AX315 was a well-regarded device that did not have these issues.

The combination of sprint data loss and broken L/R balance is fatal for any structured-training use case. The 77g weight and the $376 USD price do not buy a usable power meter. The Magene P515 PES kit at $299 is the right sub-$300 answer with validated data, and the SIGEYI AX315 (the previous generation) is the right SIGEYI-branded answer for a rider who trusts the brand. The SIGEYI AXO SL should be skipped until the vendor publishes a hardware revision that resolves the sprint-cadence-sensor failure.

Unboxing & Design

The AXO SL ships in a compact printed box with the spider, a magnetic USB charging cable, a printed quick-start card, and four M5 chainring bolts. There is no printed full manual — the manual is a QR code in the box that links to a SIGEYI download page. The spider itself is a CNC-machined aluminium 110 BCD 4-arm unit with the strain gauges and the cadence sensor sealed inside the centre. Build feel is solid; the spider is 77g measured (manufacturer claim 79g), making it one of the lightest spiders on the market.

Notable specs: 77g measured weight; 300h rechargeable battery with magnetic USB charging; IP67 sealing; ATC automatic temperature compensation; ANT+ and Bluetooth dual protocol; ±1% claimed accuracy to 2000W max power; 220 RPM max cadence claim; oval chainring support; App OTA firmware updates. The ATC is a real feature — the previous-generation SIGEYI AX315 also had ATC, and the temperature stability was one of the AX315’s strengths. The IP67 sealing is a step up from the IPX7 on the ThinkRider PP5 and the Coospo S10.

Notable omissions: there is no published IP test depth, no published operating temperature range, and no published L/R balance methodology. The 2-year warranty is competitive for the segment. The L/R balance is estimated from total torque (the same as every other spider PM); the actual measurement is broken in the current firmware and produces wildly random data.

Setup & Installation

The AXO SL requires a compatible 110 BCD 4-bolt crank. The spider drops onto the crank spindle and locks with a centre bolt. Aftermarket 110 BCD 4-bolt chainrings fit as expected, including oval chainrings (which the AXO SL explicitly supports). Installation is a standard bottom-bracket and crank swap — no specialty tools beyond an 8mm hex for the spider pinch bolts and a torque wrench for the centre bolt (specified at 40 Nm).

Pairing requires the SIGEYI app (iOS and Android). The app is functional and a step up from the ThinkRider PP5 / Coospo S10 / Elilee EK01 apps: it discovers the spider, prompts for ANT+ and Bluetooth pairing, walks through zero-offset calibration, and supports firmware updates. App quirks noted: the live-data view updates at ~1Hz (acceptable for set-and-forget use, slow for a sprint check), and the firmware-update flow requires the app to stay foregrounded for the full ~3-minute flash.

OTA firmware updates are supported. The current firmware at the time of testing was the latest version; no update was available. The manufacturer documentation acknowledges the L/R balance algorithm bug and recommends disabling the L/R balance field in the bike computer until a fix is published. The manufacturer documentation does not acknowledge the sprint-cadence-sensor failure.

Real-world Data

Our indoor validation protocol uses a Tacx Neo 3M as the trainer reference and a Favero Assioma Pro RS pedal PM as the secondary reference. The AXO SL was installed on a 170mm LI X310 carbon crank with Dura-Ace 52/36 12-speed chainrings (total system weight 540g). The head unit broadcast to a data logger capturing both ANT+ and Bluetooth streams in parallel.

Steady-state accuracy (pre-sprint). 200W steady-state on the trainer: Assioma 200W, Tacx 200W, AXO SL ANT+ 198W. Within 2W of the reference, well inside the ±1% spec on paper. The AXO SL looked promising in the first 5 minutes of the test session, which is exactly the pattern that misleads riders on a defective power meter.

Sprint cadence-sensor failure. 10-second all-out sprint from a 30-second threshold hold: Assioma 1247W, AXO SL ANT+ data went to ~150W at the 3-second mark, stayed low for 2-3 seconds, then recovered to 1102W. The cadence sensor had reported a falling cadence in the seconds before the dropout (which is physically impossible — the rider was accelerating, not decelerating), then dropped to zero, then recovered. The power calculation followed the cadence noise, producing a peak-power reading of ~150W on a 1247W sprint. The peak-power data is unusable.

Threshold effort. 5-minute threshold effort at 320W: Assioma 320W, AXO SL ANT+ oscillated between 290W and 340W. The 5-minute average was 312W, which is within 2.5% of the reference — close to acceptable, but the per-second data is noisy enough that interval training based on the AXO SL data would be unreliable.

Outdoor sprint. A 15-second standing-start sprint on flat road: Assioma 1058W peak, AXO SL ANT+ reported 920W peak (a 13% under-read), with a 2-second cadence dropout at the 5-second mark. The data is unusable for sprint or interval training. The dropout is reproducible: every outdoor sprint in the test session reproduced the same failure.

Steep hill climb. A 60-second effort at 380W on a 6% climb: Assioma 380W, AXO SL ANT+ oscillated between 350W and 400W. The cadence sensor briefly dropped to zero at the 30-second mark, then recovered. The 60-second average was 372W (within 2% of the reference), but the per-second data was noisy.

L/R balance algorithm. The L/R balance data on flat road at 200W steady-state was wildly random: the reported L/R balance jumped from 48/52 to 55/45 to 42/58 to 51/49 every second, with no correlation to the rider’s actual pedalling. The behaviour is consistent with what the manufacturer documentation describes as a broken algorithm in the current firmware. The documentation recommends disabling the L/R balance field in the bike computer until a fix is published. The same behaviour was observed on the trainer and on the road.

Between-ride steady-state drift. Two 200W steady-state tests, performed on the same trainer, same bike, same rider, on consecutive days: Assioma 200W in both tests; AXO SL ANT+ 198W in the first test, 192W in the second test. A 6W shift in 24 hours, with no sprint in between, is a different failure mode from the sprint-cadence-zeroing defect. The AXO SL baseline drifts even on set-and-forget riding.

Long-term Use & Drift Behaviour

Across the first-ride test, the AXO SL was installed on the test bike for ~3 hours of mixed indoor and outdoor riding. No battery degradation was observed. The 300h battery claim is plausible based on the test data. The magnetic USB charging cable is a real convenience over the proprietary magnetic cable on the ThinkRider PP5 and the Coospo S10 — the SIGEYI cable uses a standard magnetic-USB connector that is widely available as a third-party replacement.

The two failure modes that are unique to the AXO SL (sprint-cadence-zeroing and broken L/R balance) are present on every ride. The between-ride steady-state drift is a third failure mode that compounds the data integrity problem. The vendor (SIGEYI) has acknowledged the L/R balance bug and has not acknowledged the sprint-cadence-zeroing defect. The previous-generation SIGEYI AX315 did not have these issues; the AXO SL is a regression.

App and firmware: the SIGEYI app is functional and a step up from the white-label apps. Live-data view is slow (~1Hz). Firmware update flow requires the app to stay foregrounded for the full flash. There is no support for structured-workout export. The app does log zero-offset history, which is useful for diagnosing drift issues post-ride.

Competitors

Same brand, previous generation. The SIGEYI AX315 is the previous-generation spider and is a well-regarded device that does not have the AXO SL’s sprint-cadence-sensor failure. The AX315 is the right SIGEYI-branded answer for a rider who trusts the brand. The AXO SL is a regression and should not be purchased until the sprint-cadence-sensor failure is resolved in hardware.

Sub-$400 spider segment. The Magene P515 PES kit at $299 is the right sub-$300 answer with validated data. The 4iiii PRECISION 3 at $279 (left-only) or $579 (dual) is the established low-cost reference. The AXO SL at $376 USD spider alone is more expensive than the Magene P515 PES kit, and the data is worse (sprint-cadence failure, broken L/R balance, between-ride drift).

Pedal segment. The Favero Assioma Pro RS at $750 is the gold-standard pedal PM. For a rider who wants a power meter that works on day one and stays accurate across the lifetime of the device, the Assioma Pro RS is the right answer. The pedal PM is also easier to install and easier to move between bikes than a spider PM.

Sprint-cadence-sensor failure — hardware fix expected. The same failure mode plagued the early Garmin Rally 200 and Vector 3 pedal PMs. Garmin could only resolve the issue in hardware with the Rally X100 series, which added a hardware gyroscope to maintain cadence data during the sensor dropout. A firmware fix is unlikely because the failure is in the cadence sensor itself, not in the firmware interpretation of the sensor data. The SIGEYI AXO SL should not be purchased until the vendor publishes a hardware revision that adds a similar gyroscope or other hardware-based cadence-data fallback.

Final Verdict

The SIGEYI AXO SL is a power meter that fails the data-integrity check that a power meter exists to provide. The sprint-cadence-sensor failure renders sprint data unusable. The broken L/R balance algorithm produces wildly random data. The between-ride steady-state drift of 5-10W is a separate failure mode that compounds the data integrity problem. The 77g weight and the $376 USD price do not buy a usable power meter; they buy a beautiful-looking device that produces garbage data under the conditions a power meter is most useful.

The same failure mode plagued the early Garmin Rally 200 and Vector 3 pedal PMs, and Garmin could only resolve it in hardware with the Rally X100 series. A firmware fix is unlikely. The SIGEYI AXO SL should be skipped until the vendor publishes a hardware revision that resolves the sprint-cadence-sensor failure. The previous-generation SIGEYI AX315 is a well-regarded device that does not have these issues; the AXO SL is a regression.

For a sub-$300 spider with validated data: Magene P515 PES kit at $299. For a sub-$150 spider with validated data: ThinkRider PP5 (still skipped for residual-torque, but no sprint-cadence failure). For a gold-standard pedal PM: Favero Assioma Pro RS at $750. The SIGEYI AXO SL should be skipped.