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Garmin 810 Speed and Distance Query

Former Member over 4 years ago

My Garmin 810 (6 yrs old) appears to have acquired speed and distance problems. The speed display fluctuates as a ride along and at low speed (going uphill) it displays 0 mph even though I know I am doing about 5 mph. As I increase speed it will then jump from 5mph or so up to 14or 15 mph instantaneously. I am also finding that know routes are now measured much shorter than before and I am assuming that this is occurring because of the speed fluctuations. The clock/timing is working ok. Is this an issue with the GPS not acquiring enough satellites and so the distance/speed is now inaccurate. These errors occur on road and track with clear sky and overhanging trees etc.

Any suggestions - factory reset?

0 looigi over 4 years ago

Just for clarification, are you using a speed/wheel sensor or just relying on GPS?

0 Former Member over 4 years ago

Just relying on GPS. I have the cadence sensor on the rear wheel, but that is all

0 looigi over 4 years ago in reply to Former Member

On the wheel? A cadence sensor measures crank rpm so is usually on the crank, or the magnet type might have a magnet on the crank arm and the pickup on the the non-drive side chainstay.

There are combination sensors, like the Garmin GSC10, which has a pickup on the NDS chain stay and magnets on the crank and rear wheel spoke and picks up both cadence and speed.

Specifically which cadence sensor do you have?

0 Former Member over 4 years ago in reply to looigi

I am using the Garmin GSC10 Cadence sensor. The display for the sensor on the unit displays correctly, so I am thinking that the unit is not picking up enough satellites and so is losing accuracy during the ride. Is that a reasonable assumption and what can be done improving the picking up of the number of satellites?

0 looigi over 4 years ago in reply to Former Member

The GSC10 is both a cadence sensor and wheel/speed sensor with a cadence magnet on the left arm of the crank and a spoke magnet on the wheel. When used in this mode, it is paired as a combination speed and cadence sensor.

I believe you can also choose to pair it as only a cadence sensor, or only as a wheel sensor but not both. I have not ever done this.

In your case, is there spoke magnet on your wheel, and is the GSC10 paired as a combo sensor, cadence only sensor, or speed only sensor?

The reason I ask is because if there is a wheel sensor, and it isn't either calibrated correctly or the wheel magnet is not positioned properly with respect to the GSC10, it could cause the issue you describe.

0 Former Member over 4 years ago in reply to looigi

I have a magnet on the crank of one of my pedals and a magnet a spoke of the rear wheel. I havn't changed the battery on the Cadence sensor for a while. Could that be the cause of the error readings?

0 looigi over 4 years ago in reply to Former Member

Yes. But you also need to check that the wheel sensor magnet passes within ~6 mm (1.4") of the line scribed on the GSC10 wheel sensor arm. Some times the magnet slides a bit on the spoke and gets out of alignment, or the GSC10 pivots a bit on the chain stay so that the wheel sensor arm gets too far from the spoke magnet.

0 Former Member over 4 years ago in reply to looigi

Problem seems to have been solved. A simple change of battery to GSC10 sensor did the trick. Thanks for your comments pointing to the Cadence Sensor. Unfortunately I damaged the O Ring gasket when changing the battery. I contacted Garmin customer services to find out the size and spec of the gasket to buy a replacement and lo and behold they offered to send me a replacement - free of charge. Now that is what I call good customer service. Thanks Garmin