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# Accuracy of Garmin Watches (Read 298 times)

Longboat

More likely the treadmill is not well calibrated than the GPS is off more than a couple of percent on a medium run.  I've seen treadmills than are off by 10% on pace at running speeds.  Then some (usually cheap ones) are accurate on pace/distance, but just seem to require more effort at the same speed.

If anyone wants to try it, there are two ways to calibrate a treadmill:

1.  Manual:

Measure the length of the belt.  (used a flexible tape measure and slowly sent it through one revolution.

Put a piece of tape on it so you can count revolutions

Run the mill through one minute (or a longer time if you like), at a specific speed, while counting the number of times the tape passes the start point in that time. Make sure it's fully up to speed before starting the count.
# of passes x belt length = measured distance traveled
Speed (in MPH) x 5280 x time in minutes/60 = Calc. distance (what it should have traveled)
Correction factor = Measured distance/Calc distance.

MPH showing on mill x correction factor = real speed. (so if you're at 7 mph and the correction factor is 1.03, real speed = 7.21mph
Pace showing on mill / Correction Factor = Real pace. So 8:34 pace (=7mph) showing with 1.03 correction = real pace 8:19.

Correction factor may vary with speed , and possibly with/without a runner on the mill. You could test the runner effect at a particular speed, and/or with and without runner.

2.  Garmin Footpod:  Get a footpod for your Garmin, measure cadence and stride length at a steady pace outside, then run on the mill and compare what the Garmin says to what the mill says.  I think that may just bake in any error in the Garmin, but it's quick if you have the pod.

Neil

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Getting my Achilles back into one piece.  Now biking & water-running for cardio. Running... TBD (not soon)

I agree.  The problem is when your Garmin says 2.85 and you broke your 5K PR by two minutes.  That's when you know your Garmin is correct and the race screwed up.

Yeah, don't get me wrong, I love my GPS, but I know it's not 100% accurate.  It does bug me when people are all like "the course was advertised as X but my watch said Y, so the race director LIED!!!" and then they flip out.  A lot of my local courses have twists and turns in them which I know affects it, so if I run a PR on a course that measures 3.07 miles on my GPS, or 3.25 miles on my GPS, I count it.  They're not perfect.

Damaris
Marathon Maniac, Ultra Runner

PRs: 24:57 (5K); 51:25 (10K); 42:46 (5 Miles); 2:04:31 (HM); 4:34:09 (Marathon); 8:00 (Trail 50K)

Damaris Runs with Asthma

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