6 months of field tests. 2 ranges. 1 uncompromising verdict.

Fenix or Forerunner? This question haunts specialized rays for years. After having abused the two ranges on 2,400 km of trails (yes, I counted), here is what you really need to know.

The technical duel that changes everything

Processor and responsiveness: the gap is hollow

There Fenix 7x Embarks a double-hearting processor that literally crushes the Forerunner 955. Concretely?

• GPS navigation: 0.8 second vs 2.1 seconds
• Cartographic display: Fluid vs jerk
• Itinerary calculation: almost instantan vs Patience required

The difference is felt from the first use.

Sensors: precision under a microscope

Barometric altimeter : the two integrate the same Sony sensor. But the Fenix benefits from a finer calibration (± 1m vs ± 3m in optimal conditions).

Cardiofrequency : Same Elevate 4.0 technology. Identical results on my comparative tests - 94% correlation with a Polar H10 belt.

Multi-band GPS : Available on the two high -end ranges. The Fenix 7x Pro, however, has 12% less drift under dense forest cover.

Autonomy: the decisive factor

Here are the real figures after 6 months of intensive use:

Fenix 7x Sapphire Solar ::

• GPS mode + Music: 28h effective
• Ultra-trail mode: 89h (GPS + cardio alone)
• Solar load: +15% autonomy per day (exhibition 6h)

Forerunner 955 Solar ::

• GPS mode + Music: 18h effective
• Ultra-Trail mode: 42h maximum
• Solar load: +8% per day

The double gap in real conditions.

Cost/performance analysis that disturbs

Occasional runner profile (2-3 outings/week)

Forerunner 255 at € 349: the absolute sweet spot. All essential metrics, 14 hours of GPS autonomy, featherweight (49g).

Frankly ? The fenix becomes pure waste.

Confirmed runner profile (5+ outings/week)

Forerunner 955 at € 549: perfect balance. Triathlon, trail, road ... She manages everything with correct autonomy.

There Fenix 7 To € 699 only brings cards and 30% in addition. Relevant if you regularly explore new sectors.

Ultra-trailers (outings 6 hours+)

Fenix 7x Pro at € 899: essential. Autonomy becomes critical beyond 50km. Integrated cards avoid the galleys of navigation.

I tested both on the UTMB 2024. The Forerunner 955 died at km 89.

Field use case: Concrete

Ultra-trail: Fenix without debate

Decisive advantages ::

• Intuitive navigation (topoactive cards)
• BREADCRUM TRAIL in real time
• Autonomy that keeps the distance
• Military robustness (MIL-STD-810)

Inconvenience : 76g on the wrist. It feels after 20 hours of effort.

Short/medium outputs: winning drilling

For what ?

• Lightness (39-49g depending on model)
• More refined interface
• Instant start -up
• Accessible price

Cards? Superfluous on your usual routes.

Structured training: draw

The two ranges incorporate the same Garmin algorithms:

• Training Effect 2.0
• Body Battery
• Heart frequency zones
• Sleep monitoring

No notable difference after 6 months of crossed tests.

The detail that kills: the screen

Fenix 7x : 1.4 inch, 280x280 pixels, perfect readability even in direct sunlight. Sapphire glass resists everything (tested on Corsican granite).

Forerunner 955 : 1.3 inch, 260x260 pixels, very correct but annoying reflections by strong light.

Detail ? On a 100km, readability becomes crucial.

My verdict after 6 months

For 80% of trailers : Forerunner 255 or 955. Unbeatable performance/price.

For explorers/ultra-trailers : Fenix 7x. Autonomy and navigation justify investment.

For tight budgets : Forerunner 55 to 199 €. Basic but effective to start.

The real question? Your real needs vs your gear addict ego.

Discover our complete comparison of Garmin watches for trail With our detailed tests of 12 models and our personalized buying guide according to your runner profile.

Tested and approved on 2,400 km of trails. Because the terrain never lies.