COROS made a decision that works in your favour: their watches use standard quick-release spring bars rather than a proprietary fitting. That means band shopping comes down to one number, the lug width, and once you know it your options are wide open.
The PACE range
The PACE watches, including the PACE 3, PACE Pro and the PACE 4, generally take 20mm bands. The PACE is COROS's most popular watch by a wide margin, so this is the width most people need.
Because these are standard spring bars, a 20mm band made for a Garmin Forerunner or a Samsung Galaxy Watch fits a PACE perfectly well. You are not limited to bands labelled for COROS.
The APEX range
APEX watches take 20mm or 22mm depending on case size. The smaller cases take 20mm; the larger APEX and APEX Pro models take 22mm.
The VERTIX range
The largest COROS watches take 26mm, which is a wide band by any standard and one of the fewer sizes to shop for.
How to check yours in ten seconds
Take the current band off and measure the gap between the lugs with a ruler. You are distinguishing 20 from 22 from 26, so millimetre precision is not required.
Measure the gap, not the band. Bands are often cut a fraction narrower than the space they sit in, so measuring the band itself gives the wrong answer more often than not.
Changing a COROS band
Turn the watch over and find the small lever on the spring bar inside the band. Slide it toward the centre of the band and that end lifts away from the watch.
To fit the new one, seat one side of the spring bar in its lug hole first, then slide the lever and let the pin drop into the opposite hole. You should feel it seat. Tug each half gently afterwards to confirm.
No tool needed for quick-release bands. If a band has plain spring bars with no lever, you will need a spring bar tool.
Why standard fittings are worth something
It is easy to overlook, but this is a genuine advantage of COROS over most of its competitors. Fitbit changes band fittings between generations. Google and Samsung both use proprietary systems on some models. Apple has its own connector entirely.
With COROS, a band you buy today will fit whatever COROS watch you upgrade to next, as long as the lug width matches, and it will fit a lot of non-COROS watches too. That makes a good band a longer-term purchase than it is for most brands.
Fit and heart-rate accuracy
COROS watches read heart rate from the wrist, and that depends on consistent skin contact. The watch should sit snug about a finger's width above the wrist bone.
Too loose and the sensor reads motion rather than pulse, which shows as a heart rate that lags behind your effort or jumps during intervals. Too tight restricts blood flow and skews it the other way. Many runners wear the watch slightly higher during hard sessions and move it back down afterwards.
Shop COROS watch bands.
