What's the deal with Dual Frequency GPS?

Discussion in 'Computers/GPS SYstems' started by BonsaiNut, Feb 6, 2024.


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  1. BonsaiNut

    BonsaiNut iMTB Rockstah

    Location:
    Troutman, NC
    Name:
    Greg P
    Current Bike:
    Santa Cruz Hightower CC XX1
    Got a new dual frequency GPS watch for Christmas, and thought I would share some feedback - specifically on GPS accuracy.

    Old watch: Garmin Forerunner 645 Music (single band GPS)
    New watch: Garmin Forerunner 255 (dual band GPS)

    A lot of my biking in NC consists of winding trails with sharp turns and switchbacks. GPS devices struggle with accuracy on these trails - particularly with bikes (and faster speeds). I could use my old watch and measure a bike ride, a run, and a hike on the same trail, and get a wide range of results - always under-reporting the distance:

    Mountain biking: 8-10% under reported
    Running: 5-7% under rep0rted
    Hiking: 5% under reported

    This contrasts to a straight trail, for example, where the watch would report the same starting point, the same ending point, and even if the middle points were somewhat inaccurate, the total distance reported was usually pretty consistent.

    So when the time came for a new watch, I specifically bought one with a dual band GPS and was looking forward to testing them next to each other. Yesterday I rode a 13.0 mile trail that I ride regularly - with the 13.0 miles consistently reported via both the official trail map as well as my Cateye wheel sensor. Both watches were worn simultaneously. End result:

    Dual band: 12.29 miles (-5.5% inaccurate)
    Single band: 11.80 miles (-9.2% inaccurate)
    Actual distance: 13.0 miles

    So the dual band cut the inaccuracy by about 50%. Almost as important, the course mapping accuracy improved dramatically. Examples:

    Out and back consistency (when you travel the same trail segment out and back, does the GPS accurately portray the segments overlying each other?)

    Single band GPS:
    overlap1.jpg

    Dual band GPS:
    overlap2.jpg
    Cross-over errors. When mapping switchbacks and trail sections that run close to each other, is the GPS accurate enough to avoid showing cross-over errors? (trails inaccurately crossing over each other?)

    Single band GPS:
    crossover1.jpg

    Dual band GPS:
    crossover2.jpg
    Finally, elevation accuracy improved significantly over trails that had short climbs and drops - the single band GPS reported the trail having 344 feet of elevation(!), the dual band GPS reported 978 feet of elevation. Google Earth corrected elevation mapping suggests 1,141 feet. (Hard to tell accurately, but trail is probably around 1,400).

    Overall, I am pleased with the improvement, and am looking forward to testing both watches on runs and hikes.
     
    rollnstone, bvader, -ROCKY- and 5 others like this.
  2. da big hills

    da big hills iMTB Rockstah

    Location:
    pearl harbor
    Name:
    cagey
    Current Bike:
    enduro 29
    well now you can be two places at once
     
    herzalot, BonsaiNut, Obsidian and 3 others like this.
  3. BonsaiNut

    BonsaiNut iMTB Rockstah

    Location:
    Troutman, NC
    Name:
    Greg P
    Current Bike:
    Santa Cruz Hightower CC XX1
    I like it because according to my Garmin App I burn twice as many calories.
     
    herzalot likes this.
  4. scan

    scan iMTB Rockstah

    Name:
    fran allas
    Current Bike:
    Scott Spark
    Many times I like the Strava elevation , I usually get more. I track with my Garmin watch, single band.
     
    BonsaiNut likes this.
  5. scan

    scan iMTB Rockstah

    Name:
    fran allas
    Current Bike:
    Scott Spark
    A la Heisenberg? ;)
     
    Old&InTheWay likes this.
  6. Sidewalk

    Sidewalk iMTB Rockstah

    Location:
    The road is where I call home
    Name:
    Josh
    Current Bike:
    N+1
    If you want accurate distance, use a wheel speed sensor. GPS will always have limitations.
     
    DangerDirtyD and Rumpled like this.


As a former Amazon Associate I continue to get screwed trying to stay qualified as an Amazon Affiliate. So I quit!


Want to donate to imtbtrails?