So I'm trying to calibrate my treadmill, which feels a little faster than it indicates based on heart rate and perceived exertion, and I came up with an interesting question. The treadmill is a Sole F80, and I have it leveled so the deck is flat when the incline reads 0%.
I measured the wheel diameter with calipers at 2.35", which matches the initial calibration in the treadmill computer and what it says to use in the manual (although a sticker on the treadmill claims "2.75 in rollers"). However, if I include the thickness of the belt I get a diameter of 2.47".
Now when the belt leaves the roller at a tangent and heads over the treadmill deck, obviously the top and bottom surfaces of the belt are moving at the same speed. My question is, is that speed the same as the outer surface of the roller or is it faster? My guess is that the belt is half in compression and half in tension when it goes around the roller, and so the correct calibration diameter to use is 2.41". Incidentally, when I measured the length of the belt and counted revolutions over a set distance, 2.41" was the number I arrived at for the correct calibration, and the speed feels right effort-wise when I set it to this.
Am I thinking this through right? Did Sole really mess up the calibration on all their treadmills? After all, they did put the wrong diameter on the label. Or maybe the computer already adds a fudge factor to the roller diameter to account for the belt thickness.