Clipped_in

My 510 is paired with a GSC 10 Speed/Cadence sensor which has been working well until lately. The battery in the sensor was replace a couple of months ago. The magnet interface distances are within spec. I always run my Garmin paired to my Android smartphone and run the Livetrack feature to keep my wife happy. The Garmin unit automatically uploads activities through my phone as well.

Lately speed readings on the 510 have been very erratic. When I get done with a ride, distances on Garmin Connect for known rides are less than they should be. But here's the weird thing, when my rides are pushed to Strava the distances are more in-line with what I know they should be (with a differential between the Garmin and Strava of about 9% for the same activity). Here's an example:
Garmin Connect
Strava

So what's going on and how do I fix it? I'm guessing the problem is somehow with the GSC 10 sensor?

RocThrower

Do the distances on Garmin Connect match what your 510 displays, or are they different too? I have the 510 and same sensor, and I have only noticed very small differences in distance between GC and Strava. Nothing like the examples you posted.

Clipped_in

Good question! It hadn't occurred to me to check that until I was writing my post. I'll have a look when I get home.

gregf83 

Interesting! I just looked at my data on Garmin connect and Strava and the distances seem to match up perfectly.

i would export data from Strava and Garmin connect and compare the two rides in Excel. You should be able to see where the problem is. PM me if you want some assistance looking at the files.

I'm curious as I was contemplating getting a 510. I use an 800 and have a cadence sensor but don't think it's active as I also have an SRM which provides cadence. GPS speed is good enough for me.

Clipped_in

As have mine normally been in the past.

My real concern is not the discrepancy between Garmin and Strava, it is the erratic readings on the device. I think when I get that taken care of the rest will fall into place.

Thanks for your response!

WalksOn2Wheels

I'm going to take a stab an guess that you did this ride using the route feature on the 510. There was a known issue for the 510 being about 10% short on distances when used with a course file. I thought they fixed it in a later revision, but I haven't been on the Garmin forums in a while. I also have the 510 and noticed the problem when I used the course feature, but rarely use it now, so it hasn't been an issue.

I love my Garmin, but they seem to not be able to execute fairly simple fixes. I think it was something like 4-5 updates before they finally nailed it down.

However, the issue with using a course was buried in the file itself where there were just big gaps in the data. It also affected average speed. Perhaps Strava is using it's own distance calculation based on maps vs. what the file itself says, or some other similar correction.

WalksOn2Wheels

Here are the updates:

Garmin: Edge 510 Updates & Downloads

Looks like it was supposed to be fixed in version 2.9, but I forget when the last time I did an update was.

FLvector

When you say the speed readings are very erratic on the 510, do you mean you see the mph's jumping all over during the ride? Or do you notice this post ride?

It could be the battery life is already exhausted, so try a new battery. Another possibility is the sensor might have been slightly bumped out of place. It might still be picking up your cadence fine, but may be getting intermittent readings from the wheel magnet. In either case, if signal is lost, it will then depend on gps speed unless you have that turned off.

Clipped_in

Updates are current according to Garmin Express.

No Courses used.

Clipped_in

Yes, jumping around during the ride. I've been riding long enough to have a good feel for speed, but just to confirm during a portion of the example ride, I pedaled side by side with another rider and confirmed that the speed my unit was displaying (16 mph) was not the more accurate speed (19 mph) his Garmin was showing during that portion of the ride.

Not likely, but possible. I'll try that. I also read online that if you put the battery in backwards for about 10 seconds it shorts out the leads and resets the transmitter ID. You then install the battery normally. Has anyone here ever tried that?

The sensor and magnet positioning look fine. But, I do think that as part of whatever is happening the unit is jumping back and forth from GPS to sensor recognition for speed. Cadence seems to be consistent however.

Good responses--thanks!

BTW, the GPS and sensor unit have been in use for about 18 months.

texbiker

You must have been flying around the ride. I see on Garmin Connect your max speed was 120 mph. On my 510 Garmin Connect an Strava are almost identical. This link shows my ride today.
Cycling Texas | , Texas | Bicycling, Texas
I also use 2 other programs: SportsTrack and Golden Cheetah. SportsTrack is slightly below GC while Golden Cheetah agrees with Garmin Connect except for average speed. I also upload to RideWithGP.com to backup. This site agrees with Garmin Connect too.
You might want to consider a hard reset and since it was working and then went off track.

nwvelophile

I'd love to know more about how to analyze this data in Excel, but don't have enough postings to PM you (I tried!). Could you PM me and clarify? FYI I'm very familiar with Excel, so no help needed there. Just uncertain how to get data off Garmin in a format Excel will read. Thanks!

Willbird

I have opened a few .fit files as maybe "csv" files , meaning comma separated values ? You can read the data values, I was looking for a speed value in a trainer road file actually.

gregf83 

Sorry, I missed a step. You can export TCX files from Garmin and Strava. I looked at the TCX file for your Garmin ride and it is not recording every second. Do you have 'smart recording' enabled? That shouldn't account for the large errors but it could be a source of problem. I can't export data from your Strava ride but you can. I'll send you a PM.

Clipped_in

I changed from "Smart Recording" to 1 sec. Data shown on Garmin Connect is same as what is displayed on the Garmin unit. I carefully went through the GSC 10 sensor/magnet interfaces and that is all good. I'm beginning to believe the sensor is fine and that the problem is with the GPS unit.

Still reading slower speeds and shorter distances than what is accurate and what is displayed when uploaded to Strava. Here is last night's ride:

Garmin 39.54 mi Distance, 2:26:55 Time

Strava 43.6 mi Distance, 2:27:21 Time

While riding, speeds seem low in the 10-20mph range, but more accurate in the 20-30mph range (not including the occasional momentary outlier).

Willbird

I have looked a little trying to figure out how to export files from Garmin connect, need to get on that, and look into smart recording too :-). I want to email files to cyclemeyer and better to start sooner rather than later :-). I put like 3 months worth in and it was tedious :-)

Seattle Forrest

The FIT file your Edge records has a list of time/position/hr/power/whatever else covering your ride. But it also has a summary of all that data. I think that summary is what the device calculates and displays as you ride. Anyway, Strava ignores the summary and recalculates distance from the list of data points, eg by adding up the distance between each of them. It's not uncommon for the raw data to be pretty good and the summary to be a little off.

Clipped_in

I wanted to followup with letting those interested know that I performed a Master Reset and that seems to have solved my Garmin troubles. Thanks everyone for your input and help!
Master Reset Proceedure