Mountain Bike maps and GPS accuracy

My guess is you will still need the speed sensor for accurate disance on MTB trails. The sample rate is still 1 second so it will still cut corners without it.

I ordered one to replace my 520 plus and it will be here Friday so I'll know more about the MTB maps then. 

Hi, I selected MTB trails navigation and its found trails in the local area. I dont do MTB so no idea if its any good and i never used trail forks

Like was said already, the MTB navigation shows the trails in your area.  I don't know the source of the maps but it included all of the trails that I know about in my area.

Thanks.  I know on the older 830 and 1030, you could disable the "Trailforks base map" and still see the trails as very thin dotted lines from the included OSM data.  I think this was just all the hiking and biking trails combined.  Is this what you're seeing, or do they actually stand out more?

So far the distance on winding MTB trails has been great.  My 1030+ was always short in those conditions.  It may still be slightly short, but much improved.

The recording rate doesn't matter for distance calculation.  It's the measuring rate that matters, which is much greater than every second.  Even if you switch to smart recording where it only records a data point every few seconds, the distance will still be the same.  It's using all the info it has for distance, even if the recorded data points are cutting corners.

The only time recording rate becomes an issue is if the software you load it into throws out recorded distance and re-calculates it from the GPS points.  Strava used to do that but pretty sure it now uses the distance as recorded in the file.

Thanks - according to what you're saying I've had this all wrong.    If the 1040 is that much more accurate, I'll try a test ride with the 1040 (no speed sensor), and pair the speed sensor to my watch to compare the distance of both devices.  It may be a few weeks before my 1040 arrives but I'll try when I get a chance.

ekutter-dnu said:

The recording rate doesn't matter for distance calculation.  It's the measuring rate that matters

Generally these are the same though.  A GPS track is just a series of points in time.  I am pretty sure I read that the sample rate for the 1040 is still 1 second which would be once every 15-ish feet of distance at 10 mph.  I wonder if you what you are seeing is from better elevation data.  If you download a GPX file from Garmin Connect and open it in a text editor (like MS Notepad), are the timestamps for each track point less than a second apart?

Mine gets here today and I have a big gravel ride tomorrow.  Can't wait to start playing with it!

Sorry, but no they aren't.  GPS location can be measured multiple times a second, and is.  Even for every second recording, the distance recorded is not just the straight line between the two coordinates a second apart.  At the end of the activity, you can't accurately compute the same distance just from the recorded coordinates.  There's a lot more magic Garmin does than that.

Distance calculated just from the recorded points will be close to the recorded distance, especially on road and gravel where it's straighter, but can have big discrepancies on winding MTB trails.

Former Member The speed sensor has it's own issues on MTB trails for numerous reasons.  Try doing an out and back on a single track where you are mostly climbing one direction.  There will likely be a 1 to 3% discrepancy between the two directions, even though you did the exact same route.  With lower pressure MTB tires, I suspect part of it is the weighting, which impacts the diameter of the tire on the ground.   Plus you'll likely slightly  be cutting corners on the way up and taking the corners down slightly wider.  All adds up.  From my experience, it's usually about 2%.

For gravel or road, I no longer see any reason to have a speed sensor, other than slightly more responsive instant speed.  But I don't use it for MTB anymore either.