iPhone vs Garmin GPS Distances!

[GeorgeAndDiana]

Hello everyone!

First, a big, big THANK YOU to all of you who recommended RunKeeper. This app is outstanding and does everything I need in a running app - managing distance, pace, announcements every mile, and even managing Galloway intervals.. If you don't have this, get it!

On to my inquiry: Have any of you used both an iPhone and Garmin side by side? I've only been doing it for these initial runs with RunKeeper because ALL my 2011 data is in the Garmin Training Center, so I wanted to keep it all in one place. While using both, though, I noticed that the GPS distances reported were fairly significantly different (in my opinion).

It was a pretty nice day, so I ran about 13 miles knowing that the weekends between now and February are likely to be much, much colder her in Ohio. When I reached 13.1 miles on iPhone/RunKeeper, my Garmin read: 12.85. I ran an additional .25 just for mental reasons, but it seems to me that losing a full quarter mile every 13 seems a bit high. Has anyone else seen similar issues, and if so, which do you trust more? Just polling the crowd!

Happy training!
George

 

[RunningGirl]

I use RunKeeper on my iPhone; don't have a Garmin. Usually RunKeeper is very accurate (I run on a trail with mile markers) but if it does mess up, which it has done 2 or 3 times, it also give me more distance than I've actually run. But 99% of the time it is dead on matching the mile markers.

 

[paxsarah]

My instinct would be to trust the Garmin, because its main purpose is as a GPS, whereas the iPhone is a nifty cool gadget that does a zillion things, just one of which is GPS. I would guess that the Garmin is communicating with more satellites, etc. than the iPhone, but that's just a guess.

 

[Disfan11]

When I'm running outside, I use my Garmin watch. I download it to my Garmin site and then I convert the file so that I can upload it to my Runkeeper page. The milage always ends up being different, with Runkeeper showing slightly less miles.
Not sure why.

 

[RunRookie]

I used to use RunKeeper a lot until I got my Polar RS800CX. But I remember that RunKeeper was fairly accurate but not as good as the sports watch. But the problem was not exponential. In other words, if it is a bit off at Mile 1, it will not multiply that discrepancy each additional mile. In fact, as the iPhone GPS zeroes in better, it sends better info to RunKeeper which will put it back on track.

When in doubt, I would trust your Garmin. Especially for information on calorie burn, elevation, and cadence. The HRM will also give you a better assessment of effort when calculating calorie burn than RunKeeper could do since it is only looking at distance, speed, and maybe inclination.

 

[GeorgeAndDiana]

I'm inclined to lean towards the Garmin as well. Runkeeper is a great app - the functionality is really everything I need, including being part of the iPhone, so it by design can lower the music/podcast while it makes announcements

 

[johde]

One option that might help in figuring out which one is right is to look at the maps when you download your results. I know my Garmin 305 at times can have a small amount of variation with the marked trail I normally run. You may find one map or the other had a point or 2 that was way off.

 

[fashionista311]

The Garmin without a doubt is much more accurate. The GPS in the iPhone was never designed for running speciically

 

[GeorgeAndDiana]

My regular running path is rather GPS friendly, i.e. few trees and tall buildings, and I agree, the Garmin is probably closer to right. Too bad, though, as RunKeeper would eliminate the need for any other device if I could trust it to use it exclusively during training.

 

[fashionista311]

Even if my garmin wasnt the most accurate (which it def is) I would still prefer it. I love all the data I get when I upload to my computer, and it's much easier to keep track of pace/distance when it's on my wrist. I run with my phone as a safety thing, but I keep it tucked away and out of sight/mind. Running is *me* time.

I do agree the multiple devices are annoying...but it's the curse of our digital lifestyles!

 

[Fellowship9798]

I have a Timex GPS watch and an iPhone and took both with me on a marathon back in October. Runkeeper on the iPhone was much more accurate compared with the route markers than the dedicated Timex "Bodylink" GPS watch. The Timex was about a mile off by the end of the 26.2 miles while Runkeeper on the iPhone measured 26.07 miles.

Overall I find that Runkeeper works just fine and is accurate enough that I often don't bring anything else out with me. One device to track my distance, pace, play my music, and make a call if I run into trouble.

 

[paxsarah]

I have a Timex GPS watch and an iPhone and took both with me on a marathon back in October. Runkeeper on the iPhone was much more accurate compared with the route markers than the dedicated Timex "Bodylink" GPS watch. The Timex was about a mile off by the end of the 26.2 miles while Runkeeper on the iPhone measured 26.07 miles.

Actually, I would be surprised if you (or anyone, not you specifically) completed a properly-measured marathon and an accurate GPS measured anything shorter than 26.2 miles. Even if you ran the tangents perfectly, I don't think an accurate device would measure under the distance.

 

[Fellowship9798]

True. The measured distance should have been over 26.2 but my main point was that the iPhone actually did better than my dedicated GPS watch.

Maybe Garmin would be more accurate than Timex but for me I think Runkeeper is close enough for my training.

 

[paxsarah]

I guess my point was that you don't know that you ran only 26.2 miles - few finishers do. So if you ran over by, say, half a mile - which is fairly typical - then your devices would have split the difference and you wouldn't know which was more accurate. I think both are probably reasonably accurate enough for most runners' purposes under most circumstances either way.

 

[Fellowship9798]

I guess my point was that you don't know that you ran only 26.2 miles - few finishers do. So if you ran over by, say, half a mile - which is fairly typical - then your devices would have split the difference and you wouldn't know which was more accurate. I think both are probably reasonably accurate enough for most runners' purposes under most circumstances either way.

I see. What I probably didn't say clearly is that Runkeeper measured 26.07 miles while the Timex watch measured somewhere just over 25 miles. So in this case Runkeeper was more accurate, although still measuring short by some unknown amount.

The Timex Bodylink watch was a good first GPS watch for me, but its a few years old and fairly outdated now (the GPS receiver is a separate unit about 2/3 the size of a pack of cards worn on the arm or belt that communicates with the watch). If and when I look for another it will most likely be a Garmin as I'll know a little more about what I'm looking for.

 

[GeorgeAndDiana]

The RunKeeper/iPhone distance being longer than the Garmin ended up being a nice mental boost.. a longer distance means a faster average pace! Haha

Another multiple device consideration is trying to push start/end on multiple things as you cross the start line and finish line... luckily enough people are doing the same thing not to look at you like you're crazy!

 

[paxsarah]

I see. What I probably didn't say clearly is that Runkeeper measured 26.07 miles while the Timex watch measured somewhere just over 25 miles. So in this case Runkeeper was more accurate, although still measuring short by some unknown amount.

Aha! Yes - I was definitely assuming the Timex measured long. Oops! So in that case, both are going to be fine to get someone through a training plan and basically reach the spirit of the intended distance, but I wouldn't rely on either to help me gauge a PR attempt in process during a race.

 

[fashionista311]

Aha! Yes - I was definitely assuming the Timex measured long. Oops! So in that case, both are going to be fine to get someone through a training plan and basically reach the spirit of the intended distance, but I wouldn't rely on either to help me gauge a PR attempt in process during a race.

yes...the best way i think for the race is a good old-fashioned pace band!

 

[crewmatt]

They both have different sampling intervals and smoothingnalgorithms. I wouldn't be surprised if ruNkeeper was actually lining you up with roads rather than just tracking points which would eliminate some if what gamins see when you zigzag and don't run perfect tangents

 

[cewait]

What Matt said +1... each unit uses differing smoothing techniques and the Garmie has a better antenna. The Garmie would be though to be a little more accurate, though for our purposes... either works well.



Now get ready for all the posts on Jan 9 about the course being LONG. It is not. A GPS unit will measure long due to the fact you, the runner, are not running the shortest path on the course.