Columbus marathon GPS course measurement

You should email the race director and complain. That's not fair, man. Throw a fit and see if they can adjust your time to compensate for the .4 extra.

A Garmin watch is not that accurate. It's good enough for a workout and race pace, but not official. The wheel always measures a bit longer.

It seems like there were multiple people bringing up the same issue today. The larger crowds with narrow streets made it hard to run good tangents, and the course was a little long in general. Since it was a new start/finish area and they had you run by the Hospital chances are there was extra distance added on.

So there is NO WAY POSSIBLE that a series of 24 tracking satellites that are 12,000 miles up in the sky could possible be wrong and that it was the course. Oh okay.

Watchsocks wrote:

It seems like there were multiple people bringing up the same issue today. The larger crowds with narrow streets made it hard to run good tangents, and the course was a little long in general. Since it was a new start/finish area and they had you run by the Hospital chances are there was extra distance added on.

Extra distance was not added on. The answer is simple. GPS watches are not that accurate.

granted, the satellites make be miles away but it has been noted that these satellites can read a license plate on a Nissan Versa.

Also, the guy riding the bike with the wheel may possibly be swerving from side to side and not riding the tangents.

Bottom line: if it is tech or somebody with no Harvard education and tattoos everywhere on his skin riding a bike, most everybody will go with the tech.

This is why courses are measured with a Jones counter (according to the shortest possible distance), and NOT a GPS watch.

http://www.usatfne.org/road/coursecert.html

Sid Luft wrote:

granted, the satellites make be miles away but it has been noted that these satellites can read a license plate on a Nissan Versa.

Also, the guy riding the bike with the wheel may possibly be swerving from side to side and not riding the tangents.

Bottom line: if it is tech or somebody with no Harvard education and tattoos everywhere on his skin riding a bike, most everybody will go with the tech.

The satellites you refer to are government satellites.

The government GPS systems are much more accurate, but take a bit longer to get a signal. Commercial GPS units are meh when it comes to accuracy.

Every turn will introduce some error, combine that with not running perfect tangents and every race should show to be a little long on a GPS device. Remember that wheel measurements are done using the shortest possible route around the course.

That course has a lot of turns, a Garmin reading .2-.4 mile long over that course would not be surprising.

also, the GPS must lose the satellite signal when going through the Ohio Stadium tunnel when the course enters the field.

Sid Luft wrote:

Also, the guy riding the bike with the wheel may possibly be swerving from side to side and not riding the tangents.

That would make the course too short, not too long.

this is true.

the course would thus be long and the GPS would then be accurate if it measured the course to be long.

I was mistaken.

If the bike swerved the tattooed guy would measure 26.21875 miles but truly the course would be less than the official distance.

If the GPS was then spot on the guy running with the GPS would register a short distance.

you were correct.

Buckeye. wrote:

also, the GPS must lose the satellite signal when going through the Ohio Stadium tunnel when the course enters the field.

While it may lose the signal, if you are running in a straight line, the distance will correct itself when the signal returns. If you are making turns, then the gps will think you ran in a straight line and will show a distance less than you actually ran.

Kevin52 wrote:

Every turn will introduce some error, combine that with not running perfect tangents and every race should show to be a little long on a GPS device. Remember that wheel measurements are done using the shortest possible route around the course.

That course has a lot of turns, a Garmin reading .2-.4 mile long over that course would not be surprising.

Tangents do NOT add significant distance at all. Think about it, if you ran a 100 meter dash swerving from lane 1 all the way out to lane 8 and then back to lane 1, you would have run 101 meters. Even if the OP ran the entire race in this drunken zig-zag fashion he would not add on the extra 0.4 miles he is seeing.

1-2% of is completely normal for a GPS watch, there is no reason to invent other reasons to explain this.

Not sure if you're being facetious or not, but if you're serious, your logic is off.

IF (and that's a really big "if") the certifying bicycle was "swerving" all over, then the course would be SHORTER than measured, not longer.

Not running tangents DOES add significant distance to the course. You are correct that starting in lane 8 and running diagonally to the 100m finish line in lane 1 is only slightly longer than running in lane 1 the whole way, but that's not what the difference between running tangents and not running tangents is.

When there is a right turn on a course and then a block later a left turn, running the tangents means running a straight line between the corner at the first turn to the corner of the second turn. Most runners don't do this. Many cross the road immediately and then run along the curb to the next corner, or follow the curb for the length of the block and then cross the road at the end right before the next turn. This adds close to the width of the road in distance every time they do it.

The big reason some people see GPS measurements longer than the certified distance is because they don't run tangents like this, and many don't even run around turns along the inside edge of the turn because of crowded races. Of course that adds a lot of distance as well.

USATF/RRTC Position on GPS used by runners

Effective June 6, 2014

GPS devices work by receiving signals from satellites. The quality of different GPS units can vary, but all of them can be affected by conditions such as buildings in urban environments or heavy overhead tree cover that interfere with reception of the satellite signals and can cause them to be inaccurate.

Race courses Certified by USATF are measured by a proven method that incorporates the calibration of measuring devices against a steel tape and are verified by multiple measurements.

Race courses are measured along a well-defined path called the “SPR”—the Shortest Possible Route that a runner can possibly run. Most runners don’t actually run the SPR, so the distance recorded by their GPS device will usually be longer than the certified length of the course, even though the course was properly measured along the SPR according to USATF rules.

This is why you turn off the auto mile split on your garmin when you do a marathon. You manually hit your watch when you get to the mile markers. That will give you an accurate split between mile markers and you can adjust accordingly. It's really not that hard, it gives you something to do every 6 or 7 minutes.

In my first marathon, my watch also showed .4 too long. Instead of whining like a little biotch, I figured it out on my own and tried to run the tangents better next time. Go ahead though and put an asterisk next to your make believe time and say you broke 3 hours if the course wasn't too long.