On July 21st I ran the same 5 km loop wearing a Coros Apex 4 on my wrist and a Suunto 9 Peak Pro paired to a chest strap. Both watches were set to their highest-accuracy GPS mode — Coros on All Systems + Dual Frequency (“Max”), Suunto on Performance (GPS accuracy: Best) — so any differences in the data would come from the sensors and algorithms themselves, not from mismatched settings.
The setup
- Coros Apex 4 — wrist optical HR, GPS: All Systems + Dual Frequency
- Suunto 9 Peak Pro — HR chest strap, GPS: Best (Performance battery mode)
- Route: flat, lakeside path
The numbers
| Metric | Coros Apex 4 (wrist HR) | Suunto 9 Peak Pro (HR belt) |
|---|---|---|
| Duration | 34:46 | 34:43 |
| Distance | 4.96 km | 5.01 km |
| Avg pace | 7:01 /km | 6:56 /km |
| Avg HR | 132 bpm | 132 bpm |
| Max HR | 141 bpm | 141 bpm |
| Avg cadence | 163 spm | 164 spm |
| Avg power | 139 W | 134.7 W |
| Elevation gain | 6 m | 2.1 m |
| Elevation loss | 5 m | 38.8 m |
| Calories | 286 kcal | 230 kcal |
What matched
Average and max heart rate were essentially identical between the wrist sensor and the chest strap — a good sign for the Coros’s optical HR accuracy at steady aerobic effort. Distance, pace, and cadence were within normal GPS noise.
What didn’t
Elevation and calorie estimates diverged meaningfully. The Suunto’s barometer reported a much larger descent than the Coros — likely pressure and humidity drift rather than a real difference, since the route was flat. Calories differed by roughly 19%, reflecting different vendor algorithms rather than a sensor accuracy gap. You can read more about how weather affects barometric elevation readings and how Suunto’s battery modes affect GPS accuracy.
Takeaway
At matched top-tier GPS settings, the two watches told nearly the same story for effort and pace — but diverged once you get into derived metrics like elevation and energy expenditure.
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