Official race time vs. Garmin time (Read 1212 times)

What time do you use to keep track of your PBs? The official time of the race or the time by your Garmin? For example, two races ago the course was supposed to be 10k, and my Garmin said it was 6.58 mi... Today's race was another 10K, and my beloved Garmin 305 said it was 6.31. It's not too much of a difference (48:04 instead of 48:41), but after I've started running I've found out that I am a competitive bastard and I like to calculate as accurately as I can my PBs...

That gadget is not as accurate as you think. Read up on GPS technology and you'll never want to trust if for PRs. I live in a flat and completely open area, and mine has made two significant errors this week...one it added about .1 miles (I know by repitition where I should hit each mile on my routes), and this morning it subtracted about .05 miles within the first mile. Each time it takes a reading (probably a couple times a second), there is an error associated with it. Civilian units have an error rate of anywhere from +/- 3 feet to +/- 20 feet, depending on the weather and how many satellites you have locked. If you don't believe me, go to the instantaneous pace function and run a steady pace (or use a bike with a speedometer and go at running speeds). You will see that pace reading jumping all over the place no matter how steady you are with the pace. This is because it is going off a very small number of samples to get instantaneous pace, and the errors don't cancel out. For longer runs, since the errors are random, all but the largest ones will more or less cancel out. What you end up with is a very nice tool for running but nothing that approaches the accuracy of a measured course. If the course is measured even reasonably accurately or certified, it will blow the GPS out of the water.

TIME or DISTANCE? not at all the same thing For distance I always always always use the official distance - If they say 10K its 10K whether or not the course is certified. What your Garmin measures is not that accurate. For time I ALMOST always use official time/chip time with the exception of a few races where the start is horrendously packed and it takes a significant amount of time to actually get to the start line and they dont have chip timing. OF course that type of race is rarely a PR. And by significant I mean several minutes, not a few seconds. At least 2 minutes. I will occasionally keep watch time under those rare circumstances (and try not to do that race again usually) - but you have to make sure your garmin doesnt have autopause on or it is totally useless as a watch.

I use the official course distance and the time that shows up on my Garmin (no autopause). I usually start out at the back of the pack, and it takes me awhile to get to the start line! I'm already slow enough - I don't need to add extra seconds or minutes to my already slug-like time.

I have only these two things to add: This topic needs its own sticky or folder or whatever, cuz it do like to come up. I reconcile it thusly: I record BOTH times, but "official" is what "counts" even if I am pretty darn certain it's off (But how would I know? Feel? Comparing Garmin times with others?) And figure this (well, I guess I am adding three things, but that's OK because I placed third in my age group in today's half marathon): You could almost never hope to run the lines they use to measure, so you are but assuredly running long. Like today, when I had to shuffle around folk who had no business seeding themselves that close to the start. Relax. Have a drink. Score it how you want. Run. It ain't the Olympics.

I've had my Garmin 201 actually counting the distance backwards a couple times. For all my training I use the distance the garmin says even though I know it's not 100% accurate. It is close enough for training purposes. For the races however, I use my official times.

I've had my Garmin 201 actually counting the distance backwards a couple times. For all my training I use the distance the garmin says even though I know it's not 100% accurate. It is close enough for training purposes. For the races however, I use my official times.

HEY my "sucky old 301 that I am too cheap to upgrade" did that twice. Noone at garmin had ever heard of it. I wiped the memory and uploaded the latest software and it hasnt happend since.

There are two ways the forerunner takes a reading once every second or once every 7 seconds.......I can't imagine that once every 7 seconds would be more accurate then once a second.