>General Running>Trying to ONLY run 26.2 miles in a marathon
A Saucy Wench
I have become Death, the destroyer of electronic gadgets
"When I got too tired to run anymore I just pretended I wasnt tired and kept running anyway" - dd, age 7
If I were a race director, this would drive me batty. GPS is NOT accurate enough to measure courses!!
an amazing likeness
I've done my best to live the right way. I get up every morning and go to work each day. (for now)
So what would be a good watch to use when not using the garmin (for a marathon especially)?
Prince of Fatness
Folks tend to far overstate the issue as one of accuracy of the GPS receivers (Garmin or Polar or whomevers).
The major driver of distance differences is that courses are measured along a different line that the one we end up running due to tangents, due to not running right at the curve on the inside of each turn and corner, etc, etc. In my (limited) racing experience, I've seen people run 40' from the inside of a corner on the complete opposite road shoulder.
Recognizing that my results are just a sample of one, here are some of my Garmin vs race distances, I'd call it pretty darn accurate:
Office race distance / Garmin measured during the race
26.2 | 26.37
13.1 | 13.28
13.1 | 13.25 (same course as 13.28 above, different year)
10m | 10.04
10K | 6.27
10K | 6.25
10K | 6.23
5m | 5.04
5m | 5.02 (same course as 5.04 above, different year)
It's remarkable that they can come as close as the numbers on your list. However, .02 for 5 miles = 7.2 seconds at 6-minute per mile pace. At 8-min pace it becomes almost 10 seconds. This is quite significant, imo, and is multiplied as the distance increases. They are more than adequate for measuring practice routes and timing most workouts. However, when it comes to race distances they are just not precise enough. The course certification process is much more reliable, imo. I spent more than a half hour last spring talking to a USATF course measurer and he was very convincing.
Feeling the growl again
"If you want to be a bad a$s, then do what a bad a$s does. There's your pep talk for today. Go Run." -- Slo_Hand
I am spaniel - Crusher of Treadmills
Right on their website, Garmin claims 99% distance accuracy for the 201. I don't know what the newer versions are, but 99% as I stated earlier leaves an error of over .25 miles during a marathon. That's 2 minutes or more error for most people. Now add on top of that not running the tangents perfectly, and it is easy to see how it can read 26.6 or 26.7 no problem!
Case in point for GPS technology. I have a Garmin handheld unit, which has a much better antenna than the running versions. Recently I was in the mountains of western Montana and used it to mark a waypoint next to a tree where I had hid elk quarters from scavenging birds. I synched it up, and it tells me how well it is synched which the running versions do not -- accuracy +/- 75 feet. This was on top of a virtually treeless mountain at 7000 feet with a full view of the sky and solid lock on 4 satellites. The next day I came back and synched it up again -- accuracy +/- 86 feet locking 4 satellites. It got me within about 80 yards of the tree I was going to find, I still had to disregard it once I was in the vicinity and locate it myself.
Think about the error that +/- 75-86 feet can mean in running, and how a running watch must take a whole bunch of measurements, not just one point measurement like I was in this case.
The best example is I have seen in the past people post the track their garmin recorded plotted on some computer program overlaying an aerial map. The deviation from the road they were running on in a straight line was sometimes quite dramatic.
And the bulk of the mismeasurement of race course lengths by the Forerunner IS GPS inaccuracy, not mis-running the tangents.
I've got a fever...
On your deathbed, you won't wish that you'd spent more time at the office. But you will wish that you'd spent more time running. Because if you had, you wouldn't be on your deathbed.