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  • 310XT Accuracy?

    I am pretty sure that the 310XT is very accurate, however, I just did the Georgetown to Idaho Springs Half Marathon and my 310XT indicated that I ran 13.28 miles, when the entire distance should have been 13.10 miles. This event was not USATF certified, but that seems like a fairly decent discrepancy. Has anyone else had a similar experience, or an experience that was not like mine?

    Thanks,

    Eric

  • #2
    That's about a 1.4 percent difference. I looked over some of the races I've done with my FR305 and 310, and your difference is a little on the high side compared to my results. My largest discrepancy was the Army 10-miler, which I did with my 305, and there was a difference of 1.2 percent, when post-processed with Ascent. However, you do note that your course was not USATF certified, so it's hard to know how accurately your course was measured. Also, it would be helpful to know what your satellite accuracy was during the race (if you had this displayed). Other factors that can affect this comparison was whether or not the race was in the open or under trees or near buildings, and if the course was straight or had a lot of turns.

    For a more detailed discussion on 310 accuracy, check out this thread:

    https://forums.garmin.com/showpost.p...0&postcount=20

    Comment


    • #3
      Besides the degree of inaccuracy in the device, on longer races, it's not uncommon to run longer than the official course calls for. The course is measured on the tangent but individual runners often do not run the entire course on the tangent. They may be crowded off of the tangent lines, stick to a particular lane of the road, move from side to side to go around obstacles or catch a water stop, those little variations add up.

      Comment


      • #4
        Originally posted by JOHN313 View Post
        Besides the degree of inaccuracy in the device, on longer races, it's not uncommon to run longer than the official course calls for. The course is measured on the tangent but individual runners often do not run the entire course on the tangent. They may be crowded off of the tangent lines, stick to a particular lane of the road, move from side to side to go around obstacles or catch a water stop, those little variations add up.
        nice point, enough hair splitting already!

        Comment


        • #5
          Thanks for the reply - that definitely helps. The race was in a canyon, so it wouldn't surprise me if the accuracy was a little off, but 0.18 miles still seems high. In the events that you have done, does the distance indicated by your Garmin vary around the measured distance (sometimes high, sometimes low), or is it always long?

          Comment


          • #6
            Originally posted by EREBER View Post
            Thanks for the reply - that definitely helps. The race was in a canyon, so it wouldn't surprise me if the accuracy was a little off, but 0.18 miles still seems high. In the events that you have done, does the distance indicated by your Garmin vary around the measured distance (sometimes high, sometimes low), or is it always long?
            I think it's always been equal to or slighly higher than the advertised distance. I don't think it's ever been shorter. This is reassuring, since USATF certification actually requires the course to err on the high side so that it is at least the advertised distance. Also, as another poster pointed out, when I do a race, I'm in the middle of the pack, so I won't be able to run the tangents and the shortest distance possible.

            Comment


            • #7
              Generally, my 305s and 310 measure short (that is, in nice-ish GPS envos). Unless in urban canyons where signal bouncing on metal and glass might cause "trackpoint excursions". And on tracks, where it seems that they'd rather "forget to turn", than cut corners. A have noticed, though, that the 310 lays a better "track track" than the 305. BUT it still measures with about the same error.

              In the woods, they do tend to measure relatively much shorter than nominal. About 0.7% short in average in my experience.

              And again, in nice-ish GPS envos they tend to measure a bit short (cut corners).

              I always think of the Stockholm Marathon as 42.6 km due to the difficulty to follow the shortest path, especially around drink and food stations. Not to forget the showers (three years in a row we've had ~30C...). That's a little less than 10 meters added every kilometer. Or a little less than 1 meter added every 100 meters.
              Last edited by ALAALA; 08-10-2009, 10:38 AM.
              DISTANCE: 3000M___ - 5000M___ - 10000M__ - 21098M_ - 42195M_ --- Current VDOT: ?
              PB______: 10:50,09 - 18:40,20 - 38:39,00 - 1:25:39 - 3:10:26

              Comment


              • #8
                Originally posted by EREBER View Post
                ...., but 0.18 miles still seems high. .....

                1) How do you know you followed the exact same route they used to measure the course?
                2) How do you know they accurately measured the course?

                Given 1 and 2, I don't think you can draw any conclusions about your watch's accuracy.

                Comment


                • #9
                  I have noted a few times that the recorded 310xt distance is different from that in SportTracks , Ascent, and rubiTracks. Apparently these software packages recalculate the distance from the dataset to give a more accurate track distance. Interestingly Garmin Connect does not do this. e.g recent 5Km run measured 4.99 on the 310xt & GC, but in SportTracks and others it was revised to 4.93. Admittedly a very small difference of approx 1%, but derived from the same dataset nonetheless.

                  Comment


                  • #10
                    MotionBased recalculated distance from the data points stored rather than report what the unit reported. Similar to the other 3rd party applications.

                    One of the questions often asked at MB was "why doesn't the MB distance match my watch." For Garmin Connect, I guess they decided to try to minimize that worry by reporting what the watch says.

                    I can see arguments for both ways of doing it.

                    Initially MB had to calculate based on the trackpoints because the non-fitness units didn't (don't) report distance, only basic GPX trackpoint information. Those non-fitness units will be supported in Garmin Connect later this year, so it will be interesting to see if fitness unit users will be able to choose the non-fitness algorithm or use the unit-reported information.

                    April
                    http://www.enduranceriderblog.com

                    Comment


                    • #11
                      Originally posted by NDURANCERIDER View Post
                      One of the questions often asked at MB was "why doesn't the MB distance match my watch." For Garmin Connect, I guess they decided to try to minimize that worry by reporting what the watch says.
                      It would be nice if the user had the choice. Perhaps the default should be to report exactly what the watch says. For users that understand it, they may want to have the data corrected by GC.
                      Phil M.
                      myConnect | StravaHeatmap | Instagram
                      F201 F205 F305 FR50 310XT 920XT
                      nüvi 67LMT

                      Comment


                      • #12
                        Originally posted by ALAALA View Post
                        Generally, my 305s and 310 measure short (that is, in nice-ish GPS envos). Unless in urban canyons where signal bouncing on metal and glass might cause "trackpoint excursions". And on tracks, where it seems that they'd rather "forget to turn", than cut corners. A have noticed, though, that the 310 lays a better "track track" than the 305. BUT it still measures with about the same error.

                        In the woods, they do tend to measure relatively much shorter than nominal. About 0.7% short in average in my experience.

                        And again, in nice-ish GPS envos they tend to measure a bit short (cut corners).

                        I always think of the Stockholm Marathon as 42.6 km due to the difficulty to follow the shortest path, especially around drink and food stations. Not to forget the showers (three years in a row we've had ~30C...). That's a little less than 10 meters added every kilometer. Or a little less than 1 meter added every 100 meters.
                        I'd like to update a bit on the distance measuring part. Having some more
                        experience now with the 310 I'd say it does tend to overshoot in general
                        (the notable exception being trail runs, but there it doesn't really matter, since the Forerunners generally undershoot in the woods, so it might just
                        show better values there, less undershooting so to speak).

                        The 310 measures track work longer than the 305. Way too long: 20-30 meters per kilometer, whereas the 305 generally kept the difference at 10
                        meters per kilometer. Of course 0 meters would be the best, but it shouldn't
                        have to be worse than the 305.

                        But also, the 310 measures typical street runs in nice-ish GPS envos a bit
                        longer than the 305, perhaps 15-25 meters per 10 kilometers. This might
                        seem like minor problems to most, but why should the 310 be worse than
                        the 305? That is just plain unnecessary, to me.
                        DISTANCE: 3000M___ - 5000M___ - 10000M__ - 21098M_ - 42195M_ --- Current VDOT: ?
                        PB______: 10:50,09 - 18:40,20 - 38:39,00 - 1:25:39 - 3:10:26

                        Comment


                        • #13
                          Originally posted by ALAALA View Post
                          But also, the 310 measures typical street runs in nice-ish GPS envos a bit longer than the 305, perhaps 15-25 meters per 10 kilometers. This might seem like minor problems to most, but why should the 310 be worse than the 305? That is just plain unnecessary, to me.
                          Agreed. Maybe (hoping) these issues can be resolved in an update.
                          Phil M.
                          myConnect | StravaHeatmap | Instagram
                          F201 F205 F305 FR50 310XT 920XT
                          nüvi 67LMT

                          Comment


                          • #14
                            Originally posted by SEILOGRAMP View Post
                            Agreed. Maybe (hoping) these issues can be resolved in an update.
                            Perhaps they could introduce user selectable modes, like so:
                            - Track Mode (less aggressive calculations, tend to choose to undershoot)
                            - Normal Mode (305 style)
                            - Trail Mode (more aggressive calculations, tend to choose to overshoot)

                            Track Mode would possibly also be nice when running in urban canyons, which tends to lead to overshooting.
                            DISTANCE: 3000M___ - 5000M___ - 10000M__ - 21098M_ - 42195M_ --- Current VDOT: ?
                            PB______: 10:50,09 - 18:40,20 - 38:39,00 - 1:25:39 - 3:10:26

                            Comment


                            • #15
                              Accuracy

                              I have found all my Garmins* to be very accurate on distance. I am speaking of the Training Center mileage and not MB or GC. I run marathons and have NEVER had a 26.2 mile race. The closest I came was 26.3 and that was because the race had a blue line marking the course. It is so easy to mess up on distance...take the turns too wide, weave from side to side, don't run tangents . . . any number of possibilities.

                              My money would be on Garmin being accurate.

                              Jim

                              *One 201, one 301, two of the 205, and now a 310XT. They die after a year so I figure it is the cost of being active, $1 a day in long-term depreciation!

                              Comment

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