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 bglover11 over 8 years ago

Like you I have given up on getting any reliable pace data from the device alone.. What I've ended up doing is running with my garmin footpod with auto calibration set to on for the last month or so. I have it set up where pace is set to always but distance only indoors. So with that configuration the instant pace info is coming from the footpod and the lap pace (which I have auto-lap set to every mile) comes as a product of GPS distance/time. I have my data screens setup to show both pace and lap pace on the same screen so I can make a good comparison and see whether I need to speed up or slow down to maintain my desired overall pace goal per mile. What I've noticed is the footpod instant pace data after three or four outdoor runs is pretty accurate and jives pretty well with the lap time/pace. The first 2 or 3 tenths of every mile show lap times all over the place (due to the crappy GPS) but once you get further into every mile the fluctuations affect the overall lap pace less and less so it stabilizes and matches the footpod pretty closely. Quite the shame on a $700 device but hey.. that's for another threat right? Gotta be careful griping on this forum, you'll get an earful of "your expectations aren't realistic"... Ya... realistic. Pardon me for hoping my GPS device could pin my pace down to at least +/- one minute per mile

0 scottj2 over 8 years ago

Thanks for the insight. I'm pretty good at managing expectations, as with past devices, but this is rough...

I've used the footpod a few times with the same settings as you (auto-calibrate, outdoor pace, indoor distance). I think I've read where the shoe can make a difference. My race shoe is different than my daily trainers. I wonder if it will matter?

I have one more shake-out run on Friday. Maybe I can test the footpod one more time.

0 bglover11 over 8 years ago

Thanks for the insight. I'm pretty good at managing expectations, as with past devices, but this is rough...

I've used the footpod a few times with the same settings as you (auto-calibrate, outdoor pace, indoor distance). I think I've read where the shoe can make a difference. My race shoe is different than my daily trainers. I wonder if it will matter?

I have one more shake-out run on Friday. Maybe I can test the footpod one more time.

If it were me I would wear my race shoes on that shakeout run just in case it would make a difference with the pod. With that said, I'd also (depending on how far you were going to run) run 15 minutes and stop/save the activity so that the footpod will calibrate, then repeat for another 15 minutes and do the same before finishing out your shakeout run. This will give the pod a good couple of opportunities to adjust any final calibration numbers with the race shoes and give you the best shot of an accurate pace. That's very similar to what I did and worked just fine for me although perhaps overkill. Good luck!

0 scottj2 over 8 years ago

Sounds like a plan. I'll give it a shot tomorrow.

Thanks for your help.

0 Former Member over 8 years ago

The whole "manage your expectations" thing narks me off.

Generally when someone says it, they clearly haven't been reading peoples actual complaints; because generally people are comparing the device to another similar, but usually cheaper, device and realising that the flagship and most expensive garmin device performs worse.

Rarely is anyone complaining that the device is inaccurate with no legit basis of comparison; and I think it's certainly within reasonable expectations to assume that an £800 Garmin watch should be at least as good as a £150 Garmin watch.

0 scottj2 over 8 years ago

I agree with you. I only meant "manage expectations" in regards to legit scenarios. For example, I know the current hardware limitations around optical HRM's are going to prevent them from being 100% perfect all the time, and I'm ok with that. This GPS madness is an entirely different beast.

0 Former Member over 8 years ago

Sorry, I wasn't aiming that at you :)

It was about how some people seem to love dropping in on peoples legitimate complaint posts to "poo poo" their complaint by giving it the "expectations" speech; no one's done it in this thread yet.

0 scottj2 over 8 years ago

The day's not over yet. ;)

0 meste7 over 8 years ago

Or use DozenRun as data which can show instant pace for 3-30 seconds. Set it for 30sec if you which and will give you a decent indication of pace.

0 wojtek_b over 8 years ago

1. turn of autolap
2. lap manually at each km or mile mark
you will really wonder, how inaccurate all gps devices are.