Help with Marathon Pacing

Hi Folks.

I'm well aware of all the GPS accuracy issues, and I have contributed in the other threads. After many years and many Garmin devices, I'm so frustrated by the GPS accuracy of the Fenix 5. I wish I could return this thing. But anyway, I'm not going to waste another thread complaining. I just need some additional advice on marathon pacing.

I'm running the Buffalo Marathon this weekend and I'm very concerned I won't be able to rely on this watch for accurate GPS data. For the past couple of days, I've tried to dial in my goal marathon pace (7:50 min/mile), and I've failed miserably. I've never had this issue before. When it seems like I'm dialed in (by effort), I look at the watch and it ping pongs all over the place and then my split ends up being either way too fast or way too slow.

See attached image from last nights run, which is a suburb with no tall buildings and mostly wide open roads and sky.

Yes I know I shouldn't rely on "instant pace", but I've used these devices enough over the years to understand how to ballpark it. I've always been within 5-10 seconds of my goal splits by using a combination of effort and instant pace.

Some things I've done:
- I have the latest beta software.
- I've done a few GPS "soaks", even though it's probably not necessary.
- I always wait 5+ minutes to make sure I have both GPS and HRM lock.
- I've tested combinations of GPS, GPS+Glonass, smart recording, 1 second recording. So far GPS+Glonass with 1 second recording yields the best results for me.
- I do have a Garmin footpod, but I haven't tested it enough to trust the calibration. I wish there were a way to see both GPS pace and footpod pace.
- I installed the "Race Screen" data field so I can at least correct the splits on the fly when the GPS is inevitably off.

Am I missing anything? Anybody have any helpful hints? I'm really nervous about this marathon due to this stupid watch.

Thanks all.

0 scottj2 over 8 years ago

I've been testing the "race screen" data field rather than using the built-in manual lap feature. Hit the lap button at the split markers, and it will adjust mileage, average pace, etc, for you. Seems to work well so far.

DCRainmaker write-up: https://www.dcrainmaker.com/2016/12/pacing-races-garmin.html

0 erich1961 over 8 years ago

Does the race screen app show a more accurate pace than the native Fenix 5 screen

0 scottj2 over 8 years ago

It's just going to use whatever the built-in GPS gives it, so it won't be any more accurate. But you can adjust the time used to calculate pace from 1-60 seconds, so it should hopefully be a little more "Stable" if I adjust it to a longer interval.

I'm using it more for the lap correction feature. Every time I go by a mile marker, I can hit the lap button and it will correct the distance, avg pace, etc.

0 erich1961 over 8 years ago

Thanks, thant means no easy way to overcome the Fenix 5 pace issue.
I checked the race pace app with my 735xt and it is perfectly in sync with the native pace reading.

Still want to get a Fenix 5, but I need reasonably accurate pace data.
The 735xt is not perfect with respect to pace, in particular in forests, but overall it does the job for me.

0 cmerrill over 8 years ago

Race Screen plus footpod

I have a marathon in two weeks and have been looking for a good way to get current pace, etc. Race Screen works really well. I am using 10 second averaging for the pace and it is pretty stable on my fenix 5. I added a footpod, set to autocallibrate, outdoor speed, etc. and the pace, both instantaneous and 10 second average, is really good. I watch it through a mile and the resulting average for the mile is very consistent with the pace along the way.

Hope that helps

0 scottj2 over 8 years ago

Well, I made it through relatively unscathed. I ended up using the Race Screen data field with pace calculated at 10 second intervals. I didn't use the footpod because I haven't tested it enought to put my faith in it, although I wish I would have used it. The GPS instant pace was a bit of trainwreck as expected. Luckily the Race Screen was abe to help me recalculate the distance and avg pace.

The watch calculated 26.49 miles for what it's worth. I did my best to run the tangents, but I'm sure it wasn't perfect.

Thanks again for all the advice. Hopefully Garmin works out these GPS issues.