GPS watch accuracy on trails in the woods?

Yeah really hate it when I'm out running the same trail I do almost every day and it's always telling me different distances.

not right. GPS measures signal every 1-3 seconds. if you run on a trail that winds and turns, look at the map... you'll straight , not curved lines. I estimated .2-.4 short for trail runs around an hour. not too much but enough to mess up the pace.

I also have the Garmin Forerunner 10. I experience this as well when I am running on trails. 7:00 pace on the roads turns into 8:30-10:00 pace on the trails. The hills, turns, roots, sticks, etc. really do slow you down significantly. Now when I run trails I don't use the distance measuring capacity. I take a relatively unorthodox to getting the same stimulus for the day. If I'm hoping to run, for example, 5 miles on a certain day and I decide to run on the trails I multiply however many miles I want by 8:00. In this case that gives me 40:00. So I go to the trials and run for 40:00 and call it 5 miles in my log book. I may have not actually run 5 miles, but I ran for at least as many minutes as I would've run on the road and at a similar effort. The only reason I do this instead of simply writing down the minutes I ran is because I track my mileage, not minutes run.

You seem to be doing something very similar to what I do. I would say stick with that. As long as you are going at the correct effort for the correct amount of time, the miles don't matter. Trails are not for running fast or getting better at running fast. They are for increasing your aerobic capacity, coordination and balance while running on a soft surface.

In short, you're watch isn't wrong, trails are slow, and you should just chill out and run however many minutes you would run on the roads.

Hope this helps!

I also have the Garmin Forerunner 10. I experience this as well when I am running on trails. 7:00 pace on the roads turns into 8:30-10:00 pace on the trails. The hills, turns, roots, sticks, etc. really do slow you down significantly. Now when I run trails I don't use the distance measuring capacity. I take a relatively unorthodox to getting the same stimulus for the day. If I'm hoping to run, for example, 5 miles on a certain day and I decide to run on the trails I multiply however many miles I want by 8:00. In this case that gives me 40:00. So I go to the trials and run for 40:00 and call it 5 miles in my log book. I may have not actually run 5 miles, but I ran for at least as many minutes as I would've run on the road and at a similar effort. The only reason I do this instead of simply writing down the minutes I ran is because I track my mileage, not minutes run.

You seem to be doing something very similar to what I do. I would say stick with that. As long as you are going at the correct effort for the correct amount of time, the miles don't matter. Trails are not for running fast or getting better at running fast. They are for increasing your aerobic capacity, coordination and balance while running on a soft surface.

In short, you're watch isn't wrong, trails are slow, and you should just chill out and run however many minutes you would run on the roads.

Hope this helps!

Don't worry this happens to me too. You are not slowing down a lot. Your watch just messes it up. I have the 235 and have the same problem

Many trails actually have mile markers. I would abide by those instead of whatever number your watch gives you. Just put your watch in stopwatch mode instead of turning on its GPS.

No matter what the manufacturer says, the technology simply does not work on twisty, winding trails.

You may alternatively lose signal, but more importantly it does not triangulate, so three minutes of running may be 50 yards from the last data point if the trail doubles back.

Trail GPS wrote:

No matter what the manufacturer says, the technology simply does not work on twisty, winding trails.

You may alternatively lose signal, but more importantly it does not triangulate, so three minutes of running may be 50 yards from the last data point if the trail doubles back.

Technology doesn't work on the track either. Try it and you'll see.

I have found that I lose about 10% of the distance. This is when I'm in pretty heavy forest and frequent switchbacks.

Obviously, when going thru straighter sections, the slippage is less.

I've been through this with several watches.

While a technical trail will certainly slow your mile pace down some, I find the wearable GPS devices to be as much as 20% or more off distance wise on the trail, when compared to, for example, an iPhone or Droid device running Strava or any GPS app.

The phones can use GPS, GLONASS, AND the cellular network to triangulate your location, making them more accurate in most cases. The standard GPS watches don't have that capability.

The new Apple watch with the phone chip (or the equivalent from other manufacturers) might be the solution. I plan on trying that next.

GPS is a low energy, passive positioning system... you're hardly getting any signal under canopy, only perhaps some some scattered signal. These devices use a lot of tricks to improve their solution, like integrating accelerometer info with the gps, applying kalman filtering to the gps solutions to smooth out errors etc.

The last one likely results in 'shortening' runs with turns in it, making your pace seem slower.

I haven't seen an actual analysis of gps watch accuracy, or even their specs on their receiver & processing software (I imagine their software is proprietary) so I'm basing the above off my basic understanding of GNSS/INS systems.

Never trust technology. When running on "Pure Hate" time doesn't matter.

MAGA

235 user here. Do almost every run in thick, covered forests which leads to inaccurate distances.

Your situation is a perfect example of why it is better to go off time and not distance. Time will be the same wherever you run.

wut wrote:

235 user here. Do almost every run in thick, covered forests which leads to inaccurate distances.

Your situation is a perfect example of why it is better to go off time and not distance. Time will be the same wherever you run.

Wrong again...and again...and again...and again...etc...etc...∞...∞...∞...

Time is not always the same where I run.

Metaphysician > puny human physician

Omniscience > puny human science

Force > puny human saying: "The GPS didn't tell me to turn!"