Had enough of Garmin - recommend me something simple

[RyanH]

Unless you're OCD or doing Chung method testing, a GSC10 is kinda overkill. Even without cadence and power, head units can still provide useful information as well as preventing your phone from getting the life sucked out of it.

Keep in mind, this is coming from someone that had gone from SRM/GSC10/PC8 to no head unit and just recording everything with my phone.

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[MikeD]

GLONASS, Russia, meh... Your lucky if the satellites are working, plus it eats battery.

[Calnago]

On my ride today I took with me two GPS units (GLONASS enabled, Garmin 510 and 520). Here are the results. Both showed 49.2 miles. The max speed for one was 41.89mph and the other was 41.99mph. Enough said.

I'm assuming one of head units was paired to a calibrated speed sensor/magnet and the other was not paired with the sensor but was just using GPS data for speed. If there was no speed sensor/magnet involved and they were both simply using GPS (Glonass or not) then of course I would expect the results to be pretty much the same.
After having experimented with the Garmin hub sensor that uses the accelerometer I've gone back to a sensor/wheel magnet. It's just more reliable and I'm sure of it's accuracy. The hub sensor seemed to take a long time to even sync up with the head unit and is butt ugly strapped to a nice hub. I also have the data recording set at 1 second intervals. It's surprising to me how many people don't even delve into that stuff and are using something like "smart recording", which gives terrible map plotting when you look at it later in whatever system you use. I don't "need" the data to be perfect but I like knowing it's as good as it can be.

[pdlpsher1]

Both units are using the GPS only. I used to have a speed sensor but I took it off. The speeds that I see from the GPS are always been consistent and so I took the sensor off. Since I need the GPS turned on for Strava, having an additional sensor could only drain the battery more.

The point on my test is that the GPS is quite accurate with GLONASS. Any inaccuracies (if any) are also cumulated over the entire ride so at the end of the day you will see an accurate mileage and hence average speed.


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[Calnago]

I think GPS is quite accurate for overall distance as well. But if you ride in wooded areas with lots of canopy leaves or trees etc the GPS signal is constantly getting lost (beep, beep, beep) and it's these times where you lose the speed data that you might want to look at for a particular segment. I remember talking to Garmin once about this and they even said there's an area where they race which has a number of tunnels. Virtually everyone uses a magnet/speed sensor since the GPS signal is lost a lot. But if you're riding all the time in open areas GPS I'm sure would be very close distance wise to whatever other method you might use. And not everyone does a proper weighted rollout of the wheel to ensure they have the correct manual number entered either. The Garmin units have the ability to actually automatically "calculate" the wheel circumference based off of GPS data. Once it is calculated it stores that number in the circumference field which is then used by the attached speed sensor and magnet.

[flying]

I agree GPS distance seems quite good.
The one I wonder about a little ( not that important ) is elevation
I rode the exact same ride yesterday & today but elevation states 100" higher climb today
Just an oddity & like I said not critical just something I happened to notice today due to same ride as yesterday

[mpulsiv]

I agree GPS distance seems quite good.
The one I wonder about a little ( not that important ) is elevation
I rode the exact same ride yesterday & today but elevation states 100" higher climb today
Just an oddity & like I said not critical just something I happened to notice today due to same ride as yesterday

Was it wet and humid outside? If so, elevation is always skewed. You'd have to use auto correction in Garmin connect or Strava.

[wingguy]

GPS alone is pretty rubbish for rapid altitude changes. I believe that part of how GPSs cut down on the calculations needed to maintain location tracking when they can't see a full range of satellites is by making a baseline assumption that the earth is uniform sphere and then going from there when they can see enough satellites to tell them different. Or something like that, whatever, anyway! Pretty much any GPS unit these days will have a barometric altimeter that gives far more accurate and reliable information on rates of climb and total ascent / descent in a given ride... but then they're affected by weather systems and changes in air pressure.

Strava actually has an altitude correction function you can use which overrides your unit's altitude log with topographical data from their mapping service which should give reliable and repeatable data. But sometimes the maps have glitches. I think everyone knows a segment or two that'll give you a VAM of 10,000 because it thinks a slight downgrade is a 150ft climb.

[flying]

Was it wet and humid outside? If so, elevation is always skewed. You'd have to use auto correction in Garmin connect or Strava.

Actually no weather was quite nice today but then again Hawaii may be considered humid but I live @3500' and ride early

Thanks I did forget about that auto correct in Garmin Connect & had a hard time even finding it but knew I had seen it before. It was of course on each record
in activity section.

I did enable it & yes much closer actually..within 20 feet
Thanks will need to remember to enable it after each upload as I did not see a setting to enable by default
Lastly this is a older unit (Edge 305 )

Thanks

[pdlpsher1]

Garmin units use an altimeter for elevation. It's much more accurate than GPS but it's still not very accurate.

[Calnago]

I have a set elevation of my house in the Garmin unit. When you hit the Record button for your ride, it automatically sets the altitude to the right elevation to start. You can also do this at the start of any ride anywhere, so long as you know the actual altitude of wherever it is you're starting from.

[pdlpsher1]

I have a set elevation of my house in the Garmin unit. When you hit the Record button for your ride, it automatically sets the altitude to the right elevation to start. You can also do this at the start of any ride anywhere, so long as you know the actual altitude of wherever it is you're starting from.

Yes. I have this feature set but I believe it has no impact to the accuracy of the cumulative elevation climbed.

I once had a 510 where the altimeter just broke. It gave weird readings such as going down in elevation when I'm actually gaining elevation. It was replaced by Garmin. They gave me a refurbished 510 but it appeared new to me. The second unit is working just fine.

[jekyll man]

I think GPS is quite accurate for overall distance as well. But if you ride in wooded areas with lots of canopy leaves or trees etc the GPS signal is constantly getting lost (beep, beep, beep) and it's these times where you lose the speed data that you might want to look at for a particular segment. I remember talking to Garmin once about this and they even said there's an area where they race which has a number of tunnels. Virtually everyone uses a magnet/speed sensor since the GPS signal is lost a lot. But if you're riding all the time in open areas GPS I'm sure would be very close distance wise to whatever other method you might use. And not everyone does a proper weighted rollout of the wheel to ensure they have the correct manual number entered either. The Garmin units have the ability to actually automatically "calculate" the wheel circumference based off of GPS data. Once it is calculated it stores that number in the circumference field which is then used by the attached speed sensor and magnet.

Thats great (my 820 does it), but it relies on garmins interpretation of a distance (don't know what its requirement is, but from memory mine took about 5 minutes) based on gps coverage, which may or not be there when its calculating it. Its like assuming something to take an assumption out of an equation

Also as the newer sensors are so easy to swap from wheel to wheel, the newer garmins presumes you are using the same diameter wheel as the last time. Change bikes 26mtb.... 700*21.... 700*28, so easy for it to read incorrectly.
I'll stick with a GSC10 for the important stuff (tt bike), winter bike a new one and none on the mtb, and autocalibrate turned off.

[Calnago]

Agreed, a known fixed weighted rollout number along with a speed sensor/magnet provides me absolute assurance that all speed and distance numbers are always right.

[RyanH]

@pdlpusher I believe battery life is improved with the addition of a speed sensor since it has to process less data. I can't remember if that's true but that's what I recall.

How does the Garmin handle the GSC10 dying mid ride? I had that issue with a Lezyne and I had to restart the device and start a new ride for it to switch over to GPS.

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