GPS Accuracy
SonicDeathMonkey80
Posts: 4,489 Member
So, I just finished a half marathon today. I started the GPS on my phone via Endomondo, and it was a little ways before the actual start line. Anyway, I'm having a first-world problem figuring out if my new PR [chip time] of 1:45 is good, or my GPS time of 1:30, or possibly somewhere in between. I know some courses have discrepancies with GPS, but this seems rather large and I'm inclined to blame my phone's GPS. Anyone else have this problem with a phone's GPS or a standalone GPS? Anyhow, I'm satisfied with just breaking the 2hr mark either way, and had a lot of fun!
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I usually assume chip time is the most accurate unless there is a discrepancy in course length.0
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I've never used Endomondo but I have done runkeeper on my phone and the GPS was spotty at best once I strayed off the main roads. My garmin is far more accurate. I would go with the chip time since hopefully the course was properly measured.0
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Congrats on the PR. I'd go with chip time 15 minutes is a big gap. Hard to believe any course would be that far off0
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GPS measures distance. Not time. I don't understand the time difference? Unless you're saying that endomondo said you ran 13.1 after 1:30 even though you were still running the race? If it was a certified race course, your chip time is what counts.0
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Well, Endomondo said I ran 15.1 in 1:49, and my gun time was right around there too, so I know that was accurate at least. I started the app well before the actual start line (started at the gun). It was a trail marathon and I never lost GPS. The biggest thing I learned is that I'm no longer a 9/9:30 pace group, and I wasted a lot of energy shuffling through the groups to get where I actually belonged. I did a tune-up run a few weeks ago and was a 2:04, but I've been more active on my bike per advice from someone on here, and that really helped!0
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I think phone gps can be spotty at times. Earlier this year after 2 minutes into the Yakima Canyon Marathon my nike+ app told me I had just completed my 1st mile ( I hadn't) and was off throughout the run saying i had hit 26 miles when in reality i still had a couple of miles to go.. Definitely go with the chip time since the course is set and timing starts when you hit the line I use both a garmin and phone app when I run. Congrats by the way on your pr!0
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At a race, it's chip time that matters.
Phone GPS is not as accurate as a Garmin.
Start your GPS when you cross the start mat, not at the gun.0 -
At a race, it's chip time that matters.
Phone GPS is not as accurate as a Garmin.
Start your GPS when you cross the start mat, not at the gun.
^^ This0 -
Definitely go with your chip time - congrats on your PR!
I also always start my timer (in my case my Garmin) when I cross the start line, not when the gun goes off. Depending on the size of the race, it could be quite a while until you reach the start!0 -
On a different forum I saw someone recommend setting your GPS in the backyard, start it up, then go to bed. In the morning go back and see what distance it displays.0
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I usually assume chip time is the most accurate unless there is a discrepancy in course length.
yes, that.0 -
On a different forum I saw someone recommend setting your GPS in the backyard, start it up, then go to bed. In the morning go back and see what distance it displays.
I have done this. It said I had traveled almost 3/4 a mile in almost two hours while lying on a blanket in the shade, all but asleep.
I still use my Runkeeper app but I do not regard it as accurate for pace, only time. Since I know the length of the trails I run, it is not too big a deal. It just bugs me!0 -
Runkeeper once told me I covered 14 miles (I ran 4.3) at an astounding average pace of 4:10, I even ran a few sub 2:00 miles. I was highly impressed since I usually run 11-12 min miles. Then I saw the map. It showed I was leaping people's homes in a single bound, running across major highways (several times), I even ran through the high school and across a couple bodies of water. It was an impressive route and an Olympic caliber run. I keep that in my runkeeper just so I can remember what I can really do if I work hard enough.
My Garmin shows that I travel about 1 mile an hour while it's sitting in a window. GPS is not perfect. Certified race course is what counts.0 -
Congrats on PR!
Really quick question: where OTHER runners scratching their heads looking at their chip time? If not, then it's Endomondo.0 -
I always trust my chip time, and this trail is in the heart of Deadwood, where reception might not have always been good. Now that I know GPS isn't as accurate as previously thought, I need to figure out a way to log accurate miles so I can get into the 1:30's. Unfortunately, I can't stick to a planned route. I'm too scatterbrained. And I get bored running the same route every day. I think I'm ready to step up my casual running game into something a little more substantial like 40mi/wk.
Do y'all just run for X amount of mins and map the distance when you get home? Trust your GPS only for training purposes? Run the same memorized, tried and true routes?0 -
I always trust my chip time, and this trail is in the heart of Deadwood, where reception might not have always been good. Now that I know GPS isn't as accurate as previously thought, I need to figure out a way to log accurate miles so I can get into the 1:30's. Unfortunately, I can't stick to a planned route. I'm too scatterbrained. And I get bored running the same route every day. I think I'm ready to step up my casual running game into something a little more substantial like 40mi/wk.
Do y'all just run for X amount of mins and map the distance when you get home? Trust your GPS only for training purposes? Run the same memorized, tried and true routes?
There are so few SAFE routes here that we have little choice but use the tried and true for most of our training. I cannot stand running in little circles on a track either. I've got a measured 1.5 mile, 2.0 mile, 3.1 mile, 3.75 mile and 6.2 mile courses to choose from and just make multiple laps to get longer distances. They all have hills and flats, but some are dirt, others roadway.
BTW I define SAFE as I do not have to dive into a ditch to dodge cars nor do I need to shoot anyone's dog because they are too used to pepper spray!0 -
I always trust my chip time, and this trail is in the heart of Deadwood, where reception might not have always been good. Now that I know GPS isn't as accurate as previously thought, I need to figure out a way to log accurate miles so I can get into the 1:30's. Unfortunately, I can't stick to a planned route. I'm too scatterbrained. And I get bored running the same route every day. I think I'm ready to step up my casual running game into something a little more substantial like 40mi/wk.
Do y'all just run for X amount of mins and map the distance when you get home? Trust your GPS only for training purposes? Run the same memorized, tried and true routes?
In training, there are very few times when pace and distance matter. In order to improve as a distance runner, you need to build your aerobic engine by running easy miles (75% to 85% of MHR) over time. So, using a good old digital watch to see how long you have been running at that easy, conversational pace is really all you need. Now, when you get into specific pace workouts like a tempo run or fartlek, then you'll need an GPS to depend on. It's been well established over time that Garmin GPS watches manufactured specifically for running are far more accurate than using an app that leverages the GPS functionality on your phone.
Personally, I use my GPS watch every day, but I'm not watching pace unless it's a workout. My easy runs range between 10:30 and 8:45 pace depending upon how I feel that particular day.0 -
I have a friend who obsesses over every .1 difference between his Garmin readout and the distance a race is supposed to be (he is still complaining about a half marathon 6 months ago that Garmin had at 13.25). I will tell you the same thing I tell him: "Garmin lies, the important thing is that it lie consistently"
As Carson already pointed out Garmin is generally considered the most accurate method unless you plan on running with a measuring wheel.0 -
I have a friend who obsesses over every .1 difference between his Garmin readout and the distance a race is supposed to be (he is still complaining about a half marathon 6 months ago that Garmin had at 13.25). I will tell you the same thing I tell him: "Garmin lies, the important thing is that it lie consistently"
As Carson already pointed out Garmin is generally considered the most accurate method unless you plan on running with a measuring wheel.
Tell him that if he had run proper tangents, he would have recorded a distance that was closer to 13.1.
Also, with a certified course measurement, they build in a margin of error by adding a bit to each mile to make sure that it is definitely not under and they also measure the shortest possible distance one could possibly take around the course. So, you should never have a HM come up as exactly 13.1 if it was certified. The measurement process is details on the USATF website.0 -
I have a friend who obsesses over every .1 difference between his Garmin readout and the distance a race is supposed to be (he is still complaining about a half marathon 6 months ago that Garmin had at 13.25). I will tell you the same thing I tell him: "Garmin lies, the important thing is that it lie consistently"
As Carson already pointed out Garmin is generally considered the most accurate method unless you plan on running with a measuring wheel.
At least everyone had to run the same extra distance between start and finish.0 -
I have a friend who obsesses over every .1 difference between his Garmin readout and the distance a race is supposed to be (he is still complaining about a half marathon 6 months ago that Garmin had at 13.25). I will tell you the same thing I tell him: "Garmin lies, the important thing is that it lie consistently"
As Carson already pointed out Garmin is generally considered the most accurate method unless you plan on running with a measuring wheel.
At least everyone had to run the same extra distance between start and finish.
Not necessarily. If I run the inside tangent of every corner and you run the outside, you will have run further than me. 0 -
Typically I wear my Bluetooth HRM that syncs with my phone because it's nice to have a log of this stuff from training but this weekend during this half I'm using my Polar FT7 for a HRM to decouple that from the phone. My main reason is that I don't totally trust the phone to give me an accurate measurement for my pace and I've had the rare occasional time when it was totally way off by as much as a mile.
When I can afford it I'm getting a Garmin. For now however the phone app is a good tool and it's been pretty accurate on the distance and pace on races I've done but I don't trust it 100%. If the phone reboots or dies I can do the race just fine with nothing but a measurement of my HRM to tell me what my pace is. I have a good idea of what speed I'm running based on my pulse.
Phone GPS is accurate for the most part but don't trust it to tell you the exact distance and time.0 -
I have a friend who obsesses over every .1 difference between his Garmin readout and the distance a race is supposed to be (he is still complaining about a half marathon 6 months ago that Garmin had at 13.25). I will tell you the same thing I tell him: "Garmin lies, the important thing is that it lie consistently"
As Carson already pointed out Garmin is generally considered the most accurate method unless you plan on running with a measuring wheel.
At least everyone had to run the same extra distance between start and finish.
Not necessarily. If I run the inside tangent of every corner and you run the outside, you will have run further than me.
Considering I stagger like a drunken sailor on three-day liberty long about mile 10, I probably have covered considerably more distance. At least the opportunity for equality exists in theory
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I discussed course marking with the pacer at one of my recent marathons and he explained that if he runs a course and comes up with 26.2 he assumes it was short. The methods they use to certify the course forces them to be long when you run them and that 26.35 is about where he expects his Garmin to be for a certified marathon.Also, with a certified course measurement, they build in a margin of error by adding a bit to each mile to make sure that it is definitely not under and they also measure the shortest possible distance one could possibly take around the course. So, you should never have a HM come up as exactly 13.1 if it was certified. The measurement process is details on the USATF website.0 -
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I know sometimes (few occasions), my Motorola watch outright lied on a training run. Once it told me that I did 3 miles in 18 minutes (going for another 7 miles after that)... I knew this was a lie since I probably was 2.5 miles away from where I started. It also lies when there is a lot of cloud cover and foliage cover (lies the reverse, 15 minutes to do a mile) and I've noticed this with the garmin as well. I remember I was running an extra 8 miles sometime last year on the weekend since I was doing an unpaved trail with a lot of foliage cover. I was always tired and my husband pointed out to me that I was actually doing 8 more miles than I thought I was doing based on the distance I started and ended.
However, for the most part when I do enter races, the GPS is acurate with the chip time and the distance on the GPS is usually further than the race distance.0 -
great article!
this, from the article, is all you need to know: "Your GPS is a great tool for workouts, for figuring out approximately where you are in a race and for elevation and pacing charts."
The key word being "approximately"!0 -
LOL. I've had better. I've had Runkeeper tell me I did over 100 km on a run that was actually 10. You should have seen my speeds. LOL.
But if you keep it on your runkeeper account (without deleting the extra waypoints) then it will mess up your records/achievements, so when you really do break a speed or distance record, you don't get notified.Runkeeper once told me I covered 14 miles (I ran 4.3) at an astounding average pace of 4:10, I even ran a few sub 2:00 miles. I was highly impressed since I usually run 11-12 min miles. Then I saw the map. It showed I was leaping people's homes in a single bound, running across major highways (several times), I even ran through the high school and across a couple bodies of water. It was an impressive route and an Olympic caliber run. I keep that in my runkeeper just so I can remember what I can really do if I work hard enough.
My Garmin shows that I travel about 1 mile an hour while it's sitting in a window. GPS is not perfect. Certified race course is what counts.0 -
I discussed course marking with the pacer at one of my recent marathons and he explained that if he runs a course and comes up with 26.2 he assumes it was short. The methods they use to certify the course forces them to be long when you run them and that 26.35 is about where he expects his Garmin to be for a certified marathon.Also, with a certified course measurement, they build in a margin of error by adding a bit to each mile to make sure that it is definitely not under and they also measure the shortest possible distance one could possibly take around the course. So, you should never have a HM come up as exactly 13.1 if it was certified. The measurement process is details on the USATF website.
This is good to know. Thank you for posting!0
