How to choose a GPS mode for your race
A marathon takes about 4 to 5 hours, and the watches here claim more on GPS, so your course decides the mode. The accuracy gain from multi-band has no independent figure.
Work out how long you'll be out. Check that your watch can comfortably outlast that. Then pick the mode by what's around the course. That's the whole method, and for most road races the battery part takes ten seconds.
I don't test devices and I haven't worn any watch named here. Battery figures are makers' claims, and all of it was checked as of 3 November 2026.
Step 1: turn your race into hours
Multiply distance by pace. These are my own sums, rounded up to the minute.
Race | At 5:30 min/km (8:51 min/mi) | At 7:00 min/km (11:16 min/mi) |
|---|---|---|
5 km (3.1 mi) | 28 min | 35 min |
10 km (6.2 mi) | 55 min | 1 h 10 min |
Half, 21.1 km (13.1 mi) | 1 h 57 min | 2 h 28 min |
Marathon, 42.2 km (26.2 mi) | 3 h 53 min | 4 h 56 min |
Ultras need a slower pace to mean anything. At 9:00 min/km, 50 km (31.1 mi) is 7 h 30 min and 100 km (62.1 mi) is 15 h. At 12:00 min/km, that 100 km is 20 h. Add warm-up time, and anything you do with the watch recording before the gun.
Step 2: add a margin
My rule, and it's only that: take your expected time, multiply by 1.5, and treat that as the minimum claim. So a 4 h 56 min marathon wants at least about 7 h 24 min.
These claims come from the makers. How to read a battery claim is Gadget Otter's topic, so I won't repeat it here.
Step 3: check your watch's modes
Watch | Standard GPS mode | Multi-band mode |
|---|---|---|
Forerunner 170 | 20 h, GPS only | Not listed |
Forerunner 570 | 18 h, GPS only | 14 h, All systems plus multi-band |
Coros Pace 4 | 41 h, All systems (High) | 31 h, All systems, dual-frequency |
Suunto Run 2 | 30 h, All systems, single-band | 24 h, All systems, multi-band |
Apple Watch SE 3 | 7 h, Outdoor workout, HR on, without iPhone | Not listed |
Read that against the marathon row and you'll see my point. Up to the marathon, every one of these has room to spare on my margin except the SE 3, which falls a little short at 7:00 min/km. The big gaps between modes only start to matter for long ultras. For Ironman and beyond, best watches for ultras and Ironman sorts by GPS hours.
Step 4: pick by course
Names differ by watch, so check your manual. Garmin alone has two sets.
The Venu 4 manual (manufacturer guidance) lists GPS Only, All Systems, All + Multi-Band, Auto Select and UltraTrac. The fēnix 9 manual instead lists Max Accuracy, Normal, Extended Battery and Max Battery.
Here's how I'd choose. This is opinion, and I'll say why.
Open road, seafront, park loops. Use the standard mode. Garmin's engineer, writing on the company blog, says that in open sky GPS-only "might provide the same level of accuracy" as all systems with multi-band. It's a manufacturer's statement, but it runs against their own upsell, so I give it some weight.
City centre, tall buildings, heavy tree cover. Use multi-band or Auto Select if the battery covers it. Gilgen-Ammann and colleagues (2020, peer-reviewed, manufacturer-funded in part by Polar, JMIR mHealth) tested eight 2019-era watches with reported firmware and found distance error of 3.2% to 6.1%, worst in urban and forest settings. None of those watches had multi-band, so that shows where the problem is. It doesn't show multi-band fixes it. There's more on that in multi-band GPS explained.
Long ultra with a tight battery. Drop to the lower-power mode you need to finish. I'd avoid Garmin's UltraTrac, or the equivalent Max Battery setting, unless you have no other way to finish. Garmin's manual says UltraTrac records less often and "decreases the quality of recorded activities".
What this won't fix
No mode makes your watch agree with the course. In a survey of a 2016 half marathon, Pobiruchin and colleagues (2017, peer-reviewed, JMIR mHealth; 212 half-marathon questionnaires) found sport watches off by a mean of 0.12 km (0.07 mi). Nobody runs the exact measured line, so part of that is the runner. Those are self-reported numbers from one race.
Pace is less well known still. Average pace over a long effort inherits distance error. Instant pace is noisier, and I haven't found solid independent numbers for it on any mode or any current watch. Nor could I find an independent test of current firmware. So if you're chasing a time, I'd lean on the course's kilometre or mile markers and a lap you press yourself, and treat the live pace figure as a rough guide.
The night before
- Set the mode on your run profile, since on Garmin it's set per activity.
- Charge to full.
- Check any race-day data screens work in that mode.
- Get a GPS lock outside before the start pen fills up.
If you're still choosing a watch, see best watches for your first marathon or the first marathon picks.