Runnning road races with a Garmin

How are you so thrown off by 0.08 miles on your Garmin? Consider it an aproximation. Why dont you just race at 100% effort... Also you are in a road race. There are allowable tolerances for the measurement.The track will be too long too unless you run exactly on the inside line.

satellico wrote:

I race about once a month and for the last year I've noticed that most 5Ks register close to 3.2 miles on my Garmin. I try to pace myself using 800/mile auto lap splits but it throws me off when I see discrepancy with the race clock.

I also use the Garmin during training and prepare with specific workouts at "goal pace" further adding to my frustration. The only reliable tool is the track at this point.

Are courses purposefully measured out to be on the long side? Should I just ditch the watch and race by feel? FWIW< I'm a 16:30 5K runner.

Here has been my observation from wearing a Garmin in USTAF-certified races. If the race is hilly, my Garmin tracks me under the supposed race distance; and if the race is flat, my Garmin tracks me over the supposed race distance. Conclusion: Garmin's make a significant roundoff error when doing the trig to calculate distances up hills.

You have GOT to complain the RD. There is NO excuse for a certified course to be any more than 0.000000000000001 nm off measure. If you don't complain, whom will?

satellico wrote:

Are courses purposefully measured out to be on the long side? Should I just ditch the watch and race by feel? FWIW< I'm a 16:30 5K runner.

Are you really this obtuse?

you should ditch autolap and run by feel.

Another thing is courses are measured by shortest distance, if you don't run the tangent correct you will be a little off.

Garmins are not 100% accurate. Trees, buildings and hills can throw off the signal. I use them in races to keep an eye on my average pace, but don't expect it to be perfect.

1. The course is measured following the tangents which runners usually can't follow perfectly.

2. GPS has a inherent margin of error. You can find all kinds of stuff in old threads or on the internet on this subject.

3. The course should be as near to 5k as possible, but it is measured so that if there is any error, it is too long rather than too short.

Use the Garmin if you like for general pacing. Just don't assume that it is perfectly accurate.

txRUNNERgirl wrote:

Garmins are not 100% accurate. Trees, buildings and hills can throw off the signal. I use them in races to keep an eye on my average pace, but don't expect it to be perfect.

This.

I like to know when I have 800 meters left so I like to wear one for that.

On another note: One thing I've noticed with my Nike Sportwatch is that I'll be running, looking at the current pace and it'll read 7:15-7:30 then when I load my watch on the computer it'll say 7:45-8:00.

Weird. I suppose it could be trees, etc. I run in a neighborhood a lot of trees.

I'm going to make up some numbers to illustrate why Garmins are often too long on measured runs.

Assume you are running in an absolutely straight line for 3.1 miles.

The Garmin has an accuracy of 3 meters to your exact location (just a guess, but this is probably close).

It takes a reading every 6 seconds. (Again, a guess.)

The Garmin reads from point to point to determine distance. Imagine a circle around you 3 meters wide. The GPS might think you are anywhere in that 3 meter circle.

Sometimes it will think your position is to your left. Sometimes, to your right. Even though you are running in a straight line, the GPS thinks you are zigzagging back and forth a little bit. That adds a bit to your run. The more satellites it can see, the more accurate your position. The fewer satellites it can see, the more likely is it to think you are to the left or right of your actual position.

Also, a certified distance race must add 1% to the distance. It's part of the rules. Therefore, a certified road 5k is really 5,050 meters long.

Just to be clear, certified ROAD races must add 1% to the distance. It's part of the certification process.

fisky wrote:

Also, a certified distance race must add 1% to the distance. It's part of the rules. Therefore, a certified road 5k is really 5,050 meters long.

Actually, it's 0.1%, which is 5 meters in a 5k. 1% in a marathon would be an extra 0.26 miles, just not happening. Even my Boston race in the heat of 2012 with hitting every waterstop to dump a glass on my head and giving out 500+ high-5s, my total was 26.43, which is like 0.7%. Good tangent running reveals even smaller variance. My last 2 marathons, both with 1000s of runners on certified courses (US Air Force and Lincoln) ended up 26.28 and 26.32 miles. Roughly 0.3% over certified distance.

3.2 miles is 3% above 3.11, which for a

The people who write the software for these things understand the measurements are inaccurate and probably fit a curve to the measured points or estimate the position conditional on previous measurements

satellico wrote:

I race about once a month and for the last year I've noticed that most 5Ks register close to 3.2 miles on my Garmin. I try to pace myself using 800/mile auto lap splits but it throws me off when I see discrepancy with the race clock.

I also use the Garmin during training and prepare with specific workouts at "goal pace" further adding to my frustration. The only reliable tool is the track at this point.

Are courses purposefully measured out to be on the long side? Should I just ditch the watch and race by feel? FWIW< I'm a 16:30 5K runner.

Even if you ran a perfectly-measured, perfectly-accurate 5K and your Garmin were perfect as well, you probably would run a little more than a 5K because you are probably not perfect at running every tangent.

Just take the pace on your Garmin with a grain of salt.

jamin wrote:

Here has been my observation from wearing a Garmin in USTAF-certified races. If the race is hilly, my Garmin tracks me under the supposed race distance; and if the race is flat, my Garmin tracks me over the supposed race distance. Conclusion: Garmin's make a significant roundoff error when doing the trig to calculate distances up hills.

Actually the distance the Garmin calculates doesn't take into consideration hills. So yes a Hilly course should measure too short. However it doesn't make as much of a difference as you might think. If you run 200 meters with an elevation increase of 5 meters, then you actually ran 200.6 meters.