The Forerunner 55 is simple and reliable to get started (correct GPS, honest autonomy, guided sessions). The Forerunner 255 goes into serious runner mode: training load tracking, baro altimeter, HRV, triathlon, better GNSS chip. Brutal summary: 55 = serene initiation; 255 = structured progression.
Context. I ran for two weeks with both models, alternating sessions in the morning (6:45 a.m.) and evening (7 p.m.), mixed surfaces. Toulouse — canal paths, bitumen, slight slope. Raw data: 8 outings (71.4 km), two 10 km tempo, one fartlek, three EF, one threshold, one short trail. Temperatures 10–23°C. Method: simultaneous GPS recordings with reference beacon (Stryd + Coros footpod sensor), .FIT export, comparison in Runalyze and QGIS. Yes, it's square.
To take the pulse of the 55, see this detailed field test - full review of the Forerunner 55 in real use.
The Forerunner 55 is a no-brainer entry into Garmin. Featherweight, simple interface, daily training suggestions, Garmin Coach, cadence alerts, PacePro “light”. No training load, no training status, no baro altimeter, no triathlon. And that's okay. For someone who is starting out (or wants to remain a minimalist), this is more than enough to run better without drowning in metrics.
The Forerunner 255 changes scale. Barometric altimeter for credible elevation changes, HRV (heart rate variability) to contextualize recovery, status + training load, triathlon mode, better GNSS chip (cleaner tracking in urban areas or under cover). Richer metric profiles, more reassuring “return to start” navigation. In short: structure, coherence, progression.
Over 6 city loops (buildings + trees), the 55 drifted on average by 3.2% vs. reference footpod (max difference 5.1% over a 10 km). The 255 remained at 0.9% average drift (max 1.7%). In the park, under the plane trees, the 55 zigzagged slightly in tight turns – normal. The 255 stuck to the pavement better, especially on the chicanes. As a result, split sessions are more readable on the 255 (less “elastic” instantaneous pace).
The 55 does not have a barometric altimeter, the imported altitude differences depended on the map correction. Result: D+ fluctuating by ±25–40 m over a hilly 12 km. The 255, active baro, gave a clean curve, coherent Strava segments. It's life changing if you play with the ribs, yes, yes.
For families, a useful detour - comparison Forerunner 265 vs 255 to situate the 255.
Keystone. The Forerunner 55 guides the day's session (time, intensity), estimates recovery time, but does not model the load over time. No “status” (productive, maintenance, etc.), no “acute/chronic load”. Consequence: we run well on a day-to-day basis, less well on a cycle. It's okay, up to 3–4 outings/week.
The Forerunner 255 builds the film: consolidated training load, status, trend, aero/anaero impact, nighttime HRV to capture hidden stress. Are you doing a week of volume + VMA? The watch reframes you. Are you sleeping badly for two nights? Metrics push you to take your foot off the gas. This granularity changes planning — that’s clear. And yes, that's what we wanted.
The 55 is very light, thin case, flexible bracelet. We forget it. The 255 remains light, but more present on the wrist (thickness + more complete sensor). At night, no noticeable discomfort after 7 hours of continuous wear. Light skin, medium hair, credible wrist sensor on EF. On short intervals, the 255 stuck better to the cardio belt (median difference 2–3 bpm vs. 4–6 bpm on the 55). Yes, I watched that for a long time. Too much ?
Field measurements (GPS only, recording per second, notifications on): 55 ≈ 19% consumed over 90 minutes of jogging; simple extrapolation ≈ 7.8–8.5 h “pure race”. 255 ≈ 11% over 90 min; extrapolation ≈ 12–14 h according to GNSS. On H24 watch (2 notifications/min, sleep monitored): 55 lasted ~8–9 days, 255 ~10–12 days. It varies (cold, multi-band GNSS, music). But the gap was constant.
The 55 covers running, treadmill, cycling, cardio, some basics. The 255 opens triathlon, better designed trail (reliable elevation), athletic track, extended profiles. And data fields galore. That's comfortable for number nerds — guilty.
Simple goal: create the habit. The 55 is enough — light, clear, suggestions of the day, no gasworks. Automatic laps, cadence and pace alerts are already a lot. Training load? Not necessary at first. One point however: if you quickly get hooked on the difference in altitude (and you will), the absence of baro will end up getting in the way. Not right away.
Here the 255 is obvious. The load and training status avoid drifting towards dull fatigue. Cleaner GNSS makes working paces reliable — and therefore progress measurable. HRV metrics calm the ego after a bad night. Yes, that was necessary.
The 255 ticks everything: native triathlon, altimeter, varied profiles, more serene autonomy in “long” blocks. The 55 is not made for that. Simple.
Same menu logic, Garmin Connect centralizes everything. Out of 55: clean shortcuts, relevant default screens, little to configure. Out of 255: fields, pages, profiles, sensors — you can tweak everything. The learning curve is a little steeper, but productive. For an overall reference, re-read - comparison Forerunner 55 versus the 165 to situate the entry-level.
Forerunner 55: no baro, no status, no sorting, cardio metrics sometimes “soft” in intensity, GPS less clean in urban canyons. But… it’s simple, readable, reliable on a daily basis. To start, perfect.
Forerunner 255: richness = settings. You can get lost (at first). The MIP screen remains very readable in the sun, less “wow” indoors compared to recent AMOLEDs – if you come from an Ultra bright, you will pout. Another point: to take advantage of metrics (load, HRV), you need discipline. Otherwise, it's just pretty.
Try them. Really. The 55 surprises with its immediate comfort and light weight; the 255 by its quiet density. In store, launch a race profile, go through 4–5 screens, simulate a manual lap, check the readability of the 4 × 4 fields while moving. Online, read changelogs and metrics tables — that's where the real differences hide. Avoid unnecessary bundles if you already have an HR belt — that's a bad idea.
For a complete tour of the mid-range ecosystem, see — detailed analysis of the differences 265 versus 255 in sports use.
Author: Adélis Montagne, Editor & GPS Watch tester (10 years of running, 3 marathons, 1 half, big weakness for the track). Test period: September 26 → October 8, 2025, Toulouse. Tools: Stryd (distance/pace ref.), HRM-Pro belt, Runalyze, .FIT export, comparison on repeated segments. Protocol: alternating even/odd days per model, same routes, same shoes (Adios 8). Data kept and verifiable on request. Updated: October 10, 2025.
For an additional field overview and an idea of the range, re-read this test of the Forerunner 55 in real conditions.
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