Guides · Suunto treadmill calibration
Suunto treadmill calibration: should your watch trust the belt?
The treadmill reads 5.00 at the end of your five mile run, while your Suunto reads 4.90. You are tempted to change the watch's number to match the treadmill. Before you do, ask what that edit would teach your watch.
Suunto's help pages say to calibrate running and walking separately, each from a known distance such as a track or from connected GPS. A treadmill total is the machine's own figure. If the watch treats your edit as a calibration, it learns the belt's error too. Check the belt first.
Why your Suunto needs calibrating at all
Suunto's calibration FAQ, written for its Suunto 3 line, says that with no connected GPS the watch works out speed and distance from a motion sensor that feels your wrist move. Wrist swing and stride length vary from one person to the next. So the sensor has to be calibrated to the way you move. Until it is calibrated, the watch has no accurate speed or distance without connected GPS.
Walking and running are learned separately
Suunto's help pages tell you to calibrate running and walking on their own, because your stride changes between the two. Because the two are calibrated separately, the watch in effect keeps a separate scale for each.
So a treadmill walk tells the watch nothing about your running pace, and a run tells it nothing about your walks. If you do both indoors, your walking distance and your running distance can be off by different amounts. Fixing one leaves the other where it was.
Each of those scales works like learning the length of your own step. Walk a football field someone told you is 100 yards and count your steps, and you know what one step is worth. If that field is really 3 yards short, you will think each step is about 3 percent longer than it is. Every distance you count off after that comes out about 3 percent too long, and your feet have no way to find out. Your watch is in the same spot. It trusts whatever distance you hand it as the reference.
What Suunto means by a "known distance"
Suunto's calibration FAQ offers two routes. The easy one is to record your first runs and walks with connected GPS, and the watch calibrates itself. The manual route asks you to cover a known distance, then change the recorded distance to that known distance in the summary after the exercise. Suunto's help pages give a track as the example of a known distance.
A track makes a good reference because someone measured it. So the real question about your treadmill run is whether the machine's total counts as known. If you change the recorded distance to the treadmill total, and the watch treats that edit as a calibration, it learns the belt's error too.
Is the treadmill's total a measured distance?
It is not. On most treadmills the total comes from the same place as the speed on the display, which is the setting you picked. The belt under your feet can run faster or slower than that setting, and the total never finds out. The guide to how a treadmill gets its speed number explains why.
How far apart can they be? In one lab test of four treadmills carrying walkers and runners, each belt's average landed between 98 and 103 percent of its setting. At a 10:00 mile, 2 to 3 percent is about 12 to 18 seconds of every mile, enough that a pace you think is on target is not the pace you are running.
Say your belt runs 2 percent slow, so you really covered 4.90 miles while the treadmill counted 5.00. The watch had the closer number. Typing in the total could teach it that your stride covers 2 percent more ground than it does. Edit five runs like that in a week and your log could credit you with half a mile you never ran. If your belt runs fast instead, the edit pushes the watch the other way.
Other brands raise the same question. The guide on how another watch learns its indoor distance works through one of them.
What Suunto's pages say it needs, then what to check
Suunto's calibration FAQ asks for a steady pace for at least 15 minutes, with your normal movement, over a known distance. Suunto's help pages give a track as the example. Connected GPS can also handle it for you.
A treadmill makes the steady pace and your normal movement easy, but it often gives you no measured distance. So check the belt's real speed before you trust either number, the watch's or the treadmill's. You can do that with a handheld tachometer, which is the more accurate tool, or Treadwell. If the belt turns out to be far off, take that to your treadmill's manual or a technician. Do not let your watch quietly absorb it.
Give your watch a distance worth learning
Treadwell reads how fast the belt is moving. Take one reading at your easy run setting, such as 6.0 for a 10:00 mile, and one at your walking setting, such as 3.5, because the watch keeps those two apart. Real speed times your time on the belt, if you held one setting, gives you a distance built on a measured speed instead of a setting. To turn either real speed into a pace you can train by, the treadmill speed to pace chart lists every setting. Your watch only learns what you teach it, so teach it a distance that was real.
Check the belt before you edit the watch
Read your treadmill's real speed at the settings you run and walk at. You will need an iPhone Pro for this, since Treadwell reads the belt with its LiDAR sensor.
Scan with your iPhone Pro to get the appQuick answers
How does Suunto treadmill calibration work? Suunto's help pages say to calibrate running and walking separately, each from a known distance such as a track or from connected GPS. A treadmill total is the machine's own figure. If the watch treats your edit as a calibration, it learns the belt's error too. Check the belt first.
Is a Suunto accurate on a treadmill? It depends on what the watch learned from. Suunto's help pages say the wrist sensor has to be calibrated to your own movement, from a known distance or from connected GPS. If the distance it learned from was a treadmill total, the watch carries whatever error that belt had.
Does a treadmill walk calibrate my Suunto for running? On the watches Suunto's help pages cover, no. They say to calibrate running and walking separately, because your stride is different in each.
Sources.
- Suunto, "Why do I need to calibrate speed and distance measurement in my Suunto 3?", Suunto support FAQ, suunto.com. Without connected GPS the watch uses a wrist accelerometer that must be calibrated to your own movement; uncalibrated, it cannot measure speed and distance accurately without connected GPS; calibrate running and walking separately; connected GPS calibrates it automatically; the manual route is a steady run or walk of at least 15 minutes over a known distance, then editing the recorded distance in the summary.
- Suunto 3 Fitness user guide, "Recording an exercise", suunto.com. Calibrate running and walking separately for the best results, and use a known distance such as a track for manual calibration.
- Treadmill belt speed versus the set speed: a 2021 Scientific Reports paper by Willwacher's group (vol. 11, no. 2244) tested four lab treadmills with walkers and runners on them, and on average each belt moved at about 98 to 103 percent of what it was set to.
- My own notes: the 5.00 and 4.90 mile figures, the 2 percent slow belt and the half mile a week are a made-up example and my arithmetic, not a machine I measured. The football field is an illustration.