Last week saw the full launch of the Apple Watch Ultra 4 and Apple Watch Series 12, and both landed on my doorstep just days before I was due to tackle the Shoreditch Half Marathon in east London.
It seemed the perfect chance to test the accuracy of both watches in race conditions, especially as this particular half marathon has to fit its 13.1-mile route into quite a small area of London, so it had a lot of tight twists and turns — ideal for checking GPS accuracy.
I also strapped on a Garmin HRM-600 chest strap heart rate monitor to compare the new optical sensors on the Apple Watches, and I linked this strap to the Coros Pace 4 Pro, one of the best sports watches with multi-band GPS, for another reference point in the race.
I was impressed by the accuracy of both watches during and after the race, but each excelled in a different area — the Series 12 was a bit stronger on heart rate, while the Ultra 4 had the edge on GPS accuracy.
Let’s dive into the details.
The Apple Watch Series 12 is a lighter, slimmer and cheaper option than the Apple Watch Ultra 4, and still offers impressive sports tracking.
The Apple Watch Ultra 4 offers a more rugged design, longer battery life and more reliable GPS tracking as key upgrades on the Series 12.
GPS accuracy
I don’t think I’ve ever done a race with more turns than the Shoreditch Half Marathon, and while it’s not in an area of London with many tall buildings, the constant changes of direction made it a proper challenge for the GPS tracking on the watches.
The high number of turns also means I definitely ran further than the official half marathon distance of 13.1 miles, which is measured at the tightest racing line. I frequently had to take wide turns and weave around runners, so it’s not surprising that the watches registered a longer distance.
The two Apple Watches were almost in agreement on the total distance, with the Ultra 4 logging 13.31 miles and the Apple Watch 12 logging 13.33 miles, whereas the Coros Pace 4 Pro logged 13.22 miles.
I can’t say anything definitive about which of these distances is the most accurate — the Coros is closest to the official distance, but I did run further than that with all the turns.
However, looking at the GPS tracks, the Apple Watch Series 12 shows more minor errors than the others, veering off the road through buildings and the like. The Apple Watch Ultra 4 and Coros Pace 4 Pro produced very similar tracks for the race.
This makes sense, because the Apple Watch Ultra 4 and Coros Pace 4 Pro both have multi-band GPS, which tends to outperform the all-systems GPS on the Apple Watch 12 when in tough conditions.
It’s one of the key upgrades on the Ultra 4 over the Series 12, and while I still find the latter generally good enough on GPS accuracy, there is a benefit for opting for the Ultra 4 if you want that extra level of precision.
Heart rate accuracy
The Apple Watch 12 and Apple Watch Ultra 4 both have Apple’s new optical heart rate sensor, which the company claims is the most accurate available in a wearable based on an internal study comparing several watches to the Polar H10 chest strap.
I’ve tested every Apple Watch and found that their heart rate sensors have been particularly good for watches since the Series 4, but I do notice a difference between the Ultra and the Series models.
Even though they have the same sensor, I usually find the Series watches have more reliable heart rate tracking for me, probably because they are smaller, lighter watches that fit more snugly on my thin wrists than the weightier Ultra.
It’s important to note that if the Apple Watch you’re wearing doesn’t have a high level of confidence in the heart rate it’s sensing, it will gray out the number and not give a reading until it does.
This is what happened for me early in the race with the Apple Watch Ultra 4, which didn’t get a reliable lock on my heart rate until I was about 13 minutes in, which you can see on the graph below, noted as a straight line.
Once locked on, the Ultra 4 stayed in line with the Garmin chest strap I was wearing for the rest of the race, but the Series 12 gets the win in this category because it was in line with the chest strap for the entire race, with no grayed out sections.
Rather than going flat out from the start in the race, I ran it as a progression effort and pushed harder and harder as the race went on, producing the gradual rise in heart rate in the graph.
I quite like this approach from Apple in general — it’s better to have no reading than an incorrect one — but it does mean I couldn’t use the Ultra 4’s heart rate reading to judge effort early in the race.
Verdict
While I’ve highlighted the differences between the watches from the race, the overall performance of both was very good. Both are great sports watches as well as being among the best smartwatches.
The Ultra 4 has some extra strengths on the sports front with its multi-band GPS, longer battery life and more rugged design, but the Series 12 might be a little more reliable for heart rate, especially if you have thin wrists like mine.
I plan to do plenty more testing of both watches to get more of an insight into their performance and accuracy. Hopefully on routes that are a little more straightforward than the Shoreditch Half Marathon.
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