1760 yards

[Jezza]

Back to one of my favourite subjects...running.

I am currently training for a 100 km (62 miles) race which is to be done on a running track within 12 hours. As I am primarily a trail and woodland runner I am going through a "conversion" process of retraining to run on a track.

I normally wear a Garmin GPS tracker that determines, amongst other things my distance, time taken and speed I have it currently set at Miles. However now I am running a 400 metre track there is (apparently) a disparity between metric and imperial.

We all know that

- 1760 yards = 1609.34 metres
- A running track (inside lane) = 400 metres

So why when I reach the end of 1600 metres, or 4 laps, does my GPS unit "Beep" to tell me a mile has been completed, I mean exactly, so why the disparity of 9.34 metres?

I was running at a set pace of 1 Lap (400 m) = 2:01 mins consistently.

So to the question; Is what causes the disparity?

[JoeP]

Accuracy of the GPS unit?

Joe

[StuartR]

Did you measure the running track yourself?

Maybe it was built as a 1/4 mile running track, and they simply call it 400 meters to pretend that it is a standard size.

[steveh]

Hi Jezza

Could you be running further than you think by changing lanes or are you consistently staying in the same lane?

[Jezza]

All interesting points...

Joe - I use a Garmin ForeRunner 305 which is pretty well accurate but it has been questionable on circuits before. In one race I did it measured 36 miles instead of 37

Stuart - I checked this and it has callibration plates on all the major points

Steve - An interesting point about deviation causing extra length, I run in the inside half of the inside track, I suppose there could be a potential for extra distance. The question begs how accurate are these GPS devices?

A little maths tells me I travel around the track in 120 seconds so my speed is 3.33 metres per second or 10 feet p/s, could the combination of the above items and my speed be the reason?

[HansV]

I'd ask professor Al Bear Einstein whether it could be caused by Relativity. When you're running, time goes slower, and ...

[steveh]

Hi Jezza

I had a little Google as I am sure that you did and read some interesting accounts of people wearing this device for Iron Man competions (other sexes are available), people that have tested the accuracy in Rain, under tree's, at night etc. and all reports seem to conclude that they are very accurate.

If you are not already a member there seems to be an active group on Yahoo for the Forerunner http://sports.groups.yahoo.com/group/GarminF/" onclick="window.open(this.href);return false;

The point about speed (and that is one of the features I love with the lounge is I just saw the Al Bear message pop up) is that to my nind it cannot make a differnce because the sat nav on your car measures how far you have gone by GPRS irrespective of the speed it took to get there?

[Leif]

An interesting point about deviation causing extra length, I run in the inside half of the inside track, I suppose there could be a potential for extra distance. The question begs how accurate are these GPS devices?

My understanding is that they are only accurate to with a few metres - maybe 5-10. If you run in a straight line for 1,000M, 5M is not going to make a lot of difference. However, if you run around in a circle and the GPS system locates/tracks you 5M inside that circumference, there is room for a lot of error (depending on the circumference of the track, of course).

[Jezza]

Oh yes indeed, the only time they go really crazy, apart from the newest devices, is when you go into heavily built up areas when the satellite signal can come confused and bounce off all the high rises.

I have always wondered though what for want of a word or phrase "the pixel definition" or grid measurement is if it is 30 feet(~10 metres) then this could be the reason why there is this anomaly and the question is just snow.

Hans, OMG, if I got Al Bear Einstein onto this question Jezza Bear would drown in Cocoa (with extra marshmallows) for the length of time he would be theorising.

[jonwallace]

Does this help (or hinder)

Also see here (about halfway down the page in the "training" section) and here (which suggests you stop waving your arms about, I think . Maybe the vibration from the chainsaw...)

[ChrisGreaves]

... I run in the inside half of the inside track, I suppose there could be a potential for extra distance.

Try this thought experiment: A piece of string wrapped around the world. Of the order of 24,000 miles long, right? Now raise the string off the ground by one inch, all around the world (using small toothpicks). How much more string will you need? Surprisingly:

Spoiler

About 6 inches

.

[ChrisGreaves]

... or 4 laps, does my GPS unit "Beep" to ... why the disparity of 9.34 metres?

Out of interest, what happens at the end of your 8th lap? Are you out by 18.68 metres? After 12 laps?

[TonyE]

Maybe it is due to the Sun, or a fellow ultrarunner is jamming you.

[viking33]

... I run in the inside half of the inside track, I suppose there could be a potential for extra distance.

Try this thought experiment: A piece of string wrapped around the world. Of the order of 24,000 miles long, right? Now raise the string off the ground by one inch, all around the world (using small toothpicks). How much more string will you need? Surprisingly:

Spoiler

About 6 inches

.

What color ( colour ) toothpicks?

[Doc Watson]

So to the question; Is what causes the disparity?

You being so curious that you bothered to check, would be the root cause of the disparity. IMHO, of course.

[Jezza]

So to the question; Is what causes the disparity?

You being so curious that you bothered to check, would be the root cause of the disparity. IMHO, of course.

I have a new theory but I have to check a couple of things first

[Doc Watson]

So to the question; Is what causes the disparity?

You being so curious that you bothered to check, would be the root cause of the disparity. IMHO, of course.

I have a new theory but I have to check a couple of things first

I don't what it does to bears, but I've heard curiosity killed the cat.

[Jezza]

I have theory this may have something to do with it WAAS

[johbot]

Did you measure the running track yourself?

Maybe it was built as a 1/4 mile running track, and they simply call it 400 meters to pretend that it is a standard size.

In the lead up to the 2000 Olympi Games in Sydney, there was a TV series called The Games. One episode of that concerned the length of the 100 metre track. It was very funny.

[John Gray]

Try this thought experiment: A piece of string wrapped around the world. Of the order of 24,000 miles long, right? Now raise the string off the ground by one inch, all around the world (using small toothpicks). How much more string will you need? Surprisingly: About 6 inches.

It's actually 2Ï€" ~= 6.28". Quite easily worked out as the difference between the two circumferences 2Ï€r₁-2Ï€r₂.
Since r₁-r₂ is 1 inch, then the difference in circumferences is 2 x Ï€ x 1 ".