Terrain: autonomy, GPS, comfort (test bench)

Grip & pace stability

Departures measured: 7–12 s of typical GPS grip in open towns (55 and 245), 15–25 s sometimes with the old 45, then RAS. The instantaneous pace remains more stable at 55/245 for the first 500 meters. You can feel it in the tempo. No harmful drift in overcast skies. Really clean.

Wrist cardio

On jogging, the difference vs belt remained within ±3 bpm (55/245) and rather ±5–7 bpm on the 45 when it was cold. In short intervals (400 m), the peaks were sometimes smoothed; normal for the wrist. Acceptable. We know the song.

Readability & commands

MIP readable in direct sunlight (even at midday in summer). The 245 offers more fields per screen and its own music control. The buttons never failed in the rain. Small digression: the 55 has the best readability/simplicity “sweet spot” of the tape.

Sizes & straps

Thin wrist? The 45 comes in two sizes (45/45S). The 55 returns to a unique but balanced format, compact enough for 90% of wrists. If size bothers you, I have detailed the differences here: size differences Forerunner 45 versus 45S. This avoids a purchase that is too massive (or too small).

Autonomy: real figures vs. announced

Actual on my protocol (3 runs/week, notifications ON): 45 ≈ 5–6 days, 55 ≈ 9–12 days, 245 ≈ 5–7 days. The official figures give the trend: 45 ~7 days / ~1 p.m. GPS; 55 ~14 days / ~20 h GPS; 245 ~7 days / ~22–24 h GPS. Normal that the ground is a little lower. It's not a flaw, it's real life.

Which model for you? Concrete scenarios + purchasing experience

Quick Scenarios

• First 10 km in 8–12 weeks : take the 55 if the budget follows; otherwise 45 on sale and keep away for good shoes. That's a bad idea to pay for nothing—but the 55 takes the guesswork out of it.
• 10 km & semi with map : 55 if you always run with the phone, 245 Music if you want to go without.
• Urban jogging, safety : 45/55 is enough (incident detection + LiveTrack). And that’s reassuring.
• Long exits on unknown loops : 245 for course monitoring + return to start. Serenity > gadget.
• Zwift/Mat + 400 m track : 55 (Virtual Run + track mode) ticks the right boxes without moving up the range.

Purchasing experience: pragmatic checklist

Before clicking, look at 5 points: 1) Autonomy expected (your reports, your training volume). 2) Music : Real need to run without a phone? 3) Navigation : do you follow loops or do you improvise? 4) Height/weight : thin wrist, avoid heavy cases—try if possible. 5) Ecosystem : Garmin Coach, segments, CIQ—will you really use it? If you are hesitating between Garmin and a very performance/price oriented alternative, see the Forerunner 55 duel against Coros Pace 2 to assess the level.

Return to the store side: the “Music” kits (245) avoid the purchase of an armband, the boxes include the proprietary cable (keep it in the office if you can). Return Policies: Check 14/30 days, waterproof is no excuse if you swim in a pool (5 ATM on the range). And always test the display in direct sunlight before tearing off the label—readability is underestimated too much.

Common mistakes (to avoid)

• Choose the 245 just “for music” if you always run with the phone. Useless.
• Stay on 45 when you want a plan that adapts day after day. Take the 55.
• Ignore wrist size. Comfort > feature list. Always.

Quick summary

• Minimal budget / simplicity : Forerunner 45.
• Structured progression, better value for money : Forerunner 55.
• Without smartphone, route, music : Forerunner 245 (Music).

Official specifications: FR45 autonomy (7 days / 13 hours GPS) and 5 ATM water resistance, product manual.

Official FR55 specifications: autonomy 14 days / 20 hours GPS, profiles and functions.

FR245/245 Music specifications: autonomy and variants.

FR55 training features: Daily Suggested Workouts and PacePro (Garmin documentation).

“Back to Start” navigation and route monitoring on FR245: user manual.

Updated: October 9, 2025. Field tests carried out by David Deteve (Auterive, FR) on 18 supervised outings, raw data available on request (Garmin Connect captures). Style: direct, precise, without smoke and mirrors.