My friend claims she ran 28 miles during the Chicago Marathon. Could she possibly be that bad at tangents?

surveyor wrote:

Satellite coverage varies from day to day and hour to hour. Even if you're standing in an open field you might get a couple of one or two hour periods a day where there are only a few satellites in orbit that are visible from your location. Throw in lots of trees and buildings, and a GPS receiver might not get enough signals to calculate a location or may come up with an inaccurate one. Signals also tend to bounce off of shiny buildings ("multipathing"), which will further throw off a cheap handheld GPS.

So it's possible that the satellite coverage and geometry was just really bad in Chicago for a couple hours of this year's race, and that's why everyone's Garmins were suddenly way off.

where did you get that info?

GPS satellites are geostationary. i.e. they are all in fixed positions in the "sky". You may not be able to get their signals but they are there, always.

plus, as of now, there are several GPS satellites' signals that can be used to calculate your location on earth (you only need 3-4 of them to get a good result. With the US's, the Russian and now the Chinese GPS networks all in the sky, getting enough GPS signals should be much less an issue than a few years ago, unless your device isn't equipped to receive the signals other than those sent by US's GPS satellites, given that you're at an open location on a sunny day).

Nope...

GPS satellites fly in medium Earth orbit (MEO) at an altitude of approximately 20,200 km (12,550 miles). Each satellite circles the Earth twice a day.

Thanks for getting it right.

Obviously my info was wrong. Somehow I (mis)remembered the GPS satellite orbits were geostationary (~40K km). I did check that several years back. My memory failed me.

Anyway, even just with the US GPS network (24 satellites), at a given open spot on earth, one should be able to get signals from AT LEAST 4 GPS satellites at any time on a sunny day.

rojo wrote:

pm222 wrote:

The final time that showed on my Garmin was exactly matched with my official race time, but the Garmin showed a final distance of 28.47 miles.

I'm glad it dose something right for $200. It can tell time.

Then again people are now paying $500 for a apple watch.

So you have the time, right?

And you have mile markers?

You can also just do the math. Right?

Right, people? Can you? CAN YOU?!?!?

HardLoper wrote:

They should make the GPS watches know that you're running the Chicago Marathon, and base the distance off of known checkpoints. If your location is at the 15 mile mark of the race it should assume you have been running for 15 miles. This would be more accurate than the current method.

This is quite right.

Even if the woman used something like a mobile phone that uses cell towers to enhance gps accuracy, the app that's recording the running doesn't know it's on a road. The site where she uploaded the track to doesn't know she's on a road either.

They make lots of junky numbers and pretty pictures. A marathon that is too long should be a clue it's all time wasters.

If a race has mile markers why would I need to use a GPS watch?

Alan

I got 26.73

Almost all of it was mile 13 where it showed I ran 4.34

I was running extra most of the way as I started in the 2nd corral for 3.15 runners and ran 2.51 (Until the day before I was in corral F for 4.01 to 4.15!)

my first mile seemed acurate even with underpass 6.38 GPS 6.41 on my timex.

But my GPS really doesn't matter (Garmin 15) They have offical results that tell me what I ran.

not my normal self wrote:

your arithmetic is OK, but your application of it is quite nonsensical

You ever see the way some runners navigate a race course? That is what is quite nonsensical. A few years ago I was measuring a course for certification and needed a police cruiser escort for a highway section. The guy who drove protection for me was doing the race, and when we finished up he told me he was amazed at the way I was riding the tangents. He said he always just runs down the middle of the roads because he doesn't look ahead. I ran into him a few weeks after the race and he told me he tried to run the way I had been riding and his Garmin showed over 2/10 shorter for him that year vs the year before.

Runningart2004 wrote:

If a race has mile markers why would I need to use a GPS watch?

Alan

If you run Detroit a few of the mile markers are guaranteed to be 1/4 mile or more off.

This is reason #15234532423 why people glued to their watch's pace during a marathon are doomed to miss their goal time.

Runningart2004 wrote:

If a race has mile markers why would I need to use a GPS watch?

Alan

I was thinking the same thing.

A watch that takes splits and checking the mile markers is all you need.

I thought a GPS watch was for you you didn't have a measured course or mile markers.

I think technology is taking away runner's abilities to get a feel for their running pace and effort.

I've never had a GPS watch.

I'm still pretty good at judging a distance that I have run on an unmarked route by my time and effort.

When I go back and measure it online or some other method, I'm pretty close to my estimate.

I have been reading these threads for years and I have come to the conclusion that gps devices provide the perfect excuse for some people not reaching the expectations!

Others have said it, but since moving to the Midwest I've been in Chicago numerous times. The GPS on my car and phone are always all messed up. Especially on my phone -- it has a lot of trouble precisely figuring out where I am. I'm sure that's the reason.

I just want to add that a lot of people are really bad at running tangents. They see the street about to curve and immediately get to the inside, moving left and right all over the place. They SHOULD look ahead and take the straightest route to the bend, gradually getting to the inside. I just ran 2:46 and measured 26.31 on good tangent running. The guy behind me measured 26.45 and was all over the road. I thought any sub-3 person should know better.

GPS doesn't work in tunnels. It also doesn't work well between tall buildings and over bridges. It's officially called multi-path interference. There is no solution.

Garmins allow footpod switching, which seems perfect for Chicago. Footpod at the start, switch to GPS later.

I ran the Chicago Marathon three times in the mid-2000s. I'd hate to venture a guess on the exact measurement, but I can imagine you could add a lot on by not running the tangents and weaving around thousands of runners.

To give you a sense of the congestion if you haven't run it before, my first year running Chicago, I was in the 2nd corral. I ran 3:07 that year (7:08 pace) and my opening mile was 8:48 purely because I was so packed into the crowd of runners I could hardly move. By the second mile I was still crowded in but was able to run 7:51. Finally, by the third mile things started to spread out enough that I was able to settle in at 7:00-7:10 pace. I bit the bullet the first two miles, telling myself it wouldn't be that hard to make up 5 seconds a mile or so over the next 24-25 miles, versus the energy I would have expended fighting through the crowd of runners early on, trying to move in and out of hundreds of people, weaving all over the road.

If someone is really trying to go around all those people, weaving every which direction and they are far enough back that the crowd of runners that it doesn't thin out until much further into the race, I could see that really adding up over the duration of the race. It would be magnified even more if they were not paying attention to tangents on all the turns.

so much GPS confusion wrote:

GPS doesn't work in tunnels. It also doesn't work well between tall buildings and over bridges. It's officially called multi-path interference. There is no solution.

Garmins allow footpod switching, which seems perfect for Chicago. Footpod at the start, switch to GPS later.

Ok, it doesn't work in tunnels, but, does GPS melt steel beams?

I have never used GPS and probably never will.

Maybe I'm lucky but I always have a pretty good idea of where I am, and I could always maintain pace without needing my watch.