Why does my garmin constantly measure short? Even on certified courses

Your gamin doesn't measure anything. It determines your position to within 15 meters 95% of the time. The gamin algorithm then takes all of these segments and smooths out the path to ESTIMATE where it thinks you ran. You can find this information on yhe gamin website and also on the many articles on wiki. There are actually the data of people who tested their gaming doing multiple trials and have actually plotted it on maps. If this is your cup of tea it's pretty cool stuff.

Your GPS gadget doesn't work like wayz.

It just logs points with pretty bad accuracy. It doesn't matter if you are viewing it on some website or not. Garbage in, more garbage out.

it sounds like it is losing satellite coverage.

It measures tangents between two points, so if you take any turns the distance will show up as less than the actual distance.

That's what you like to tell yourself huh. "No baby, its reallly 8 inches, the measuring tool is wrong!"

Why would he call himself "baby"?

I have done stranger things in my life, let me tell you that, baby

"Even on certified courses"

Hilarious

Gee, I'm a Tree! wrote:

It measures tangents between two points, so if you take any turns the distance will show up as less than the actual distance.

Actually it doesn't measure the distance between points. Garmin knows that each individual data point isn't very accurate. It continually samples where it thinks you are (within 15m 95% of the time), then through a smoothing algorithm takes the data points and through a probabilistic determination it guesses the path that it thinks you took.

If you run 20m it could be way off on both a nominal measure and a percentage measure. If you run a mile, the nominal accuracy could be the same as your 20m run, but the percentage accuracy becomes very small.

A good link

On my old Forerunner 305 you can choose the frequency that it checks the satellite. If you choose 'every second' it increases accuracy but runs the battery down faster.

Garmins aren't usually that short on a certified course of that distance. Maybe the course was certified but the course was set up wrong.

Could it be a satelite issue? Doesn't a garmin usually sync with 4 or 5 satelites when it starts up? Seems like the more the better accuracy. If a garmin starts with only 2 satelites (is that possible?) would the accuracy be off? I have no idea. Just wondering outloud.

garmin skeptic in the making wrote:

I ran a 10k last week where my garmin forerunner 610 said I ran 5.91 miles. The race was USATF certified and I didn't take any wrong turns as this is a big race that I've ran several years. I'm not sure what the deal is.

It seems like the faster the pace the more it's off. I was doing 1k repeats in about 3 minutes on the road with my friend today on a loop that we know to be 1k but I had my garmin on anyway and it kept showing 0.56 instead of 0.62.

If anyone has any advice that would be greatly appreciated. Thanks!

You have a long arm swing. Every time you swing your arm back , you minus that amount from your run. Try running with your arms by your side next run.

ive got the 610 as well and seems to consistently measure 5% shorter than when i map the run. you can upload your runs to garmin connect and it will give you your route. mine usually hacks off turns.

but it is also off on straights. i did an experiment of running on a straight road until it beeped at 1 mile, turned around and ran until it beeped for the second mile. i was about 50m short of where i started

Turk wrote:

On my old Forerunner 305 you can choose the frequency that it checks the satellite. If you choose 'every second' it increases accuracy but runs the battery down faster.

I second this recommendation. My Garmin was consistently underestimating distances until I increased the sampling frequency. Now it's far more accurate.

GPS measurer wrote:

garmin skeptic in the making wrote:

I ran a 10k last week where my garmin forerunner 610 said I ran 5.91 miles. The race was USATF certified and I didn't take any wrong turns as this is a big race that I've ran several years. I'm not sure what the deal is.

It seems like the faster the pace the more it's off. I was doing 1k repeats in about 3 minutes on the road with my friend today on a loop that we know to be 1k but I had my garmin on anyway and it kept showing 0.56 instead of 0.62.

If anyone has any advice that would be greatly appreciated. Thanks!

You have a long arm swing. Every time you swing your arm back , you minus that amount from your run. Try running with your arms by your side next run.

Can't believe nobody else brought this up.

Additionally OP, if there is also a satellite connectivity issue going on, which sounds like there is, there is one fool-proof way to check this - run your next run or workout with your garmin arm raised above your head. This will keep your body from interfering with the connection & blocking the satellite signal. It's important for this trial to be at least 5 or 6 miles to get a true test. Any shorter distance will have too many other variables and will waste your time.

Ding ding ding wrote:

GPS measurer wrote:

You have a long arm swing. Every time you swing your arm back , you minus that amount from your run. Try running with your arms by your side next run.

Can't believe nobody else brought this up.

Additionally OP, if there is also a satellite connectivity issue going on, which sounds like there is, there is one fool-proof way to check this - run your next run or workout with your garmin arm raised above your head. This will keep your body from interfering with the connection & blocking the satellite signal. It's important for this trial to be at least 5 or 6 miles to get a true test. Any shorter distance will have too many other variables and will waste your time.

Since you notice the discrepancies at faster running speeds, I would definitely do these test runs no slower than tempo pace. Better yet if you can do it at time trial speed, or even in a 10k race setting.

Do this in your next certified 10k & you'll probably find it measures accurately.

Thanks for the idea!! Would it work even better if I strapped it around my neck and put an antenna on it that goes up, say 4 feet above my head?

Gee, I'm a Tree! wrote:

It measures tangents between two points, so if you take any turns the distance will show up as less than the actual distance.

This is the correct answer.