Edge 800 - GPS is FXXXXX

steelem

hi guys only had this garmin a month - so 4th time out today - windy day - set my course 25.18 miles off i go - i notice all the way round the speed was jumping from 25mph down to 11mph even down to zero - when i finished the course my unit gave a distance of 18.56 miles avg speed 13mph- so not only did it lose 6.5 miles my average is normally around 18 mph-- either i have a fault with the unit or its not been w.i.n.d tested - anyone else with this unit please let me know your thoughts - im proper peed off ..

amaferanga

Do you have a speed/cadence sensor and if so have you set wheel size manually?

steelem

i have cadence yes - no havent set manual?

amaferanga

Try manually setting your wheel size and then report back

steelem

are we saying then the gsc10 sensor does the speed??? why does'nt the gps???

magliaceleste

The GPS does. The GSC10 can improve accuracy, e.g. when no sat signal is available.

Personally I've found the GSC10 more trouble than they are worth. To me it sounds as simple as the wheel magnet and sensor not being close enough or a battery voltage issue.

However, do check your wheel size as suggested.

steelem

i thought the whole idea of GPS was accuracy - all i want it to do is gps measure speed gsc 10 do cadence - can this unit do that ??

amaferanga

steelem wrote:

i thought the whole idea of GPS was accuracy - all i want it to do is gps measure speed gsc 10 do cadence - can this unit do that ??

If you set the wheel size right you'll get better speed accuracy from the GSC-10. Garmin change how different units work all the time - on a previous firmware release for my Forerunner 310XT the GSC-10 was used for speed all the time (regardless of whether or not GPS was enabled), but then they changed it so GPS is used unless its disabled where the GSC-10 is then used. And they didn't even think to mention this change in the notes that accompanied the firmware update....

magliaceleste

steelem wrote:

i thought the whole idea of GPS was accuracy - all i want it to do is gps measure speed gsc 10 do cadence - can this unit do that ??

Hang on...are you saying you have a GSC10 which you are using for cadence (with a cadence magnet) but you don't have a magnet on the wheel for the speed?

If so, that might be your problem. The GSC10 is a combined unit, so the Garmin may be trying to get speed from the wheel but not getting anything (apart for the crank magnet)

Either that or the magnet on the wheel/sensor is too far away or the battery is duff.

steelem

no its all set up correctly wheel magnet gsc 10 cadence magnet - this is the problem the unit is not getting the data properly from the gsc 10 in windy conditions thats why it was going to 0 etc .. not sure why setting the wheel manually would make any difference - & have no idea why using a speed magnet on the wheel would be of better advantage than gps. its just crazy

amaferanga

You can use the GSC-10 for cadence only - I've done this in the past.

steelem

ps it was also losing cadence from time to time on todays ride.. i can deal with that but losing speed / distance is just a farce - especially forking 350-00 out

steelem

amaferanga wrote:

You can use the GSC-10 for cadence only - I've done this in the past.

how do i do this ??

steelem

looks like i found the setting to turn off the speed on the gsc 10 - hurray

TMR

steelem wrote:

i thought the whole idea of GPS was accuracy - all i want it to do is gps measure speed gsc 10 do cadence - can this unit do that ??

My Garmin Edge 500 does precisely this and I don't have any issues. I don't even have the wheel magnet mounted.

spasypaddy

steelem wrote:

amaferanga wrote:

You can use the GSC-10 for cadence only - I've done this in the past.

how do i do this ??

just remove the wheel magnet. its what i did about 6 months ago. no problems whatsoever. however about to start using my turbo so will be putting it back on

Scrumple

The 800 will calculate speed off the sensors by default, overriding GPS.

It does this as it is more accurate than GPS.

If you climb a steep hill for a long distance, the satellites see you have covered a few miles in a straight line. They do not see you have travelled further, due to altitude (think triangles, you clumb the longer axis).

Like other posters have said, you can force it to use GPS for speed. It wont be as accurate, but still ok.

rolf_f

Scrumple wrote:

If you climb a steep hill for a long distance, the satellites see you have covered a few miles in a straight line. They do not see you have travelled further, due to altitude (think triangles, you clumb the longer axis).

Go and calculate the difference between the two sides of the triangles on your chosen hill and then get back to us!

FWIW though, the magnet must be better assuming you have got the settings right - and more consistent.

eh

i thought the whole idea of GPS was accuracy

Not when it comes to speed measurement, better to get a direct measure off the wheel.

rhext

Sounds a bit dodgy to me. I have an Edge 200 and the only time it displays symptoms like you describe is when it loses satellite reception. And that never seems to happen while it's out in the open, so I'd question whether you've got a fault. Wind certainly shouldn't affect it. Can't comment on the auxiliary sensors!

1_reaper

I had a problem a while back and all the problem was that through our crappy roads the magnet had moved a few mil's in alignment with the sensor arm.. re aligned it and had no problems since

steelem

the magnets are all in place - checked again- had no issues before - but it was so windy today ....

Secteur

I have wheel size set to default in the Garmin 800 settings.

How do I measure what mine actually is, to make it most accurate?

The garmin default is 2089mm - I have no idea what mine actually is.

Is it a case of marking the tyre, rolling it one full revolution and measuring the distance covered?

boblo

Secteur
Is it a case of marking the tyre, rolling it one full revolution and measuring the distance covered?

yes

on-yer-bike

My 800 loses satellite reception every now and then out in the open. Not sure if this would effect the distance speed calculations as it can probably join up the dots.

leech

I had a similar problem with my 800. Changed the battery in the GSC10 and it's been fine since.

It's worth a try.