Garmin Rally vs Apple Watch Ultra 3: Cycling Power vs GPS Watch

Overview

These two products are not direct competitors and comparing them requires some context. The Garmin Rally is a cycling power meter pedal system designed to measure wattage output on the bike. The Apple Watch Ultra 3 is a premium GPS multisport smartwatch. A cyclist might own both simultaneously, using the Rally pedals to feed power data to a head unit while wearing the Ultra 3 for GPS, heart rate, and recovery tracking. If you arrived here wondering which to buy instead of the other, the answer depends entirely on what problem you are trying to solve.

Specs at a glance

Device type: Garmin Rally is a pedal-based power meter; Apple Watch Ultra 3 is a GPS smartwatch
GPS: Garmin Rally has no GPS chipset; Ultra 3 has dual-frequency L1/L5 GNSS with multi-constellation support
Heart rate: Garmin Rally has no HR sensor; Ultra 3 has wrist optical PPG with HRV
Battery: Garmin Rally rated 90 hours (internal rechargeable); Ultra 3 rated 72 hours low-power, 18 hours standard GPS workout mode
Power measurement: Garmin Rally measures cycling watts at +/- 1% accuracy; Ultra 3 has no power meter capability
Display: Garmin Rally has no display; Ultra 3 has always-on microLED with sapphire crystal
Water resistance: Garmin Rally is cycling-specific; Ultra 3 rated 100m WR with EN13319 dive certification
Connectivity: Garmin Rally transmits via ANT+ and Bluetooth to head units; Ultra 3 connects to iPhone ecosystem

GPS and tracking accuracy

The Garmin Rally has no GPS chipset. It measures power, cadence, and force metrics at the pedal and transmits that data to a separate cycling computer or head unit. GPS tracking is entirely handled by whatever device you pair it with.

The Apple Watch Ultra 3 is one of the strongest GPS performers in the smartwatch category. Its dual-frequency L1/L5 GNSS setup beats the Garmin Fenix 8 in satellite acquisition benchmarks and outperforms the Garmin Forerunner 965 in open-water swim GPS accuracy. For wrist-based GPS during swimming, that is a meaningful real-world advantage for triathletes.

Battery life

The Garmin Rally pedals are rated at 90 hours on a single charge, which covers a full season of typical training blocks before needing to plug in. For most cyclists doing 10 to 15 hours per week, that is roughly six weeks of riding.

The Apple Watch Ultra 3 delivers approximately 18 hours in standard GPS workout mode. That is enough for a Half Ironman with careful management, but it falls short for full Ironman or ultra-endurance events. The 72-hour low-power mode extends range significantly but reduces GPS and sensor fidelity. For multi-day events, this is a hard limitation.

For athletes: who wins?

Cycling power data: Garmin Rally. No watch can replace a dedicated strain-gauge power meter at the pedal. The Rally 210 adds left/right balance at +/- 1% accuracy that the Ultra 3 simply cannot provide.
Running and trail: Apple Watch Ultra 3. The Rally pedals are useless off the bike. The Ultra 3 handles GPS tracking, heart rate via wrist optical PPG, and altimeter data across all disciplines.
Triathlon: Both, used together. Use the Rally pedals on the bike leg for accurate power data fed to a head unit, and wear the Ultra 3 for GPS, swim tracking, and overall race recording.
Recovery monitoring: Apple Watch Ultra 3. Skin temperature, SpO2, and HRV via wrist optical PPG give the Ultra 3 a full recovery tracking toolkit. The Rally pedals collect no off-bike data whatsoever.

Verdict

Comparing the Garmin Rally to the Apple Watch Ultra 3 is comparing a precision instrument to a multi-tool. Serious cyclists who train with power need the Rally or a similar pedal-based meter because no wrist device replicates what a strain-gauge pedal delivers. Athletes who train across multiple disciplines and want a single device for GPS, health tracking, and smartwatch functions should buy the Ultra 3. If you are a cyclist asking which replaces the other, neither does. If you are a non-cyclist trying to choose a sports tracker, the Garmin Rally is irrelevant to your decision and the Apple Watch Ultra 3 stands on its own as a top-tier GPS watch. Buy the Rally if you need cycling power data. Buy the Ultra 3 if you need a GPS multisport watch.