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Speed/cadence incorrect speed/distance

timpiej
over 8 years ago
Hi

In 2012 I bought a Garmin Edge 800 bundle. So with HR monitor, speed & cadence sensor. About a year ago I sold my Edge 800 and bought me an Edge 1000.
So I'm using the accessories of the Garmin Edge 800 (only sold the head unit) with the headunit of Edge 1000.

Recently I went for some rides in the UK with a couple of friends. My distance was way of compared to there's. We went for a 95 km ride, they finished with these 95-100km and I finished with 75km. Then later that week we did the Prudential RideLondon 100 Surrey. They finished with 160-163 km, my distance kept it at an 140 km.

I also noticed that sometimes I would have speed drops, like when riding 28 km/h it would drop to 14,6 km/h (for example) for about 5 seconds and then jump to 28km/h again. I also noticed this yesterday when not even pedaling anymore.

On my ride yesterday I've used the Edge 1000 (with the cadence sensor) and the Garmin Forerunner 910xt (on GPS) so I could compare. The distance didn't differ too much (99,56 km on the Edge 1000 and 103,12km on Forerunner 910xt) but the average speed had a big difference: Edge 1000 had an average speed of 25,9 km/h while my forerunner said I had 26,8 km/h average.

I have a green light on the speed/cadence sensor when the speed magnet passes and a red when my cadence magnet passes. I don't think this will help finding the problem, but I'd just share anything I've found out.

I know there's a margin for errors on the different types of GPS and sensors. But a difference of over 20km in distance or 1km/h average seems alot to me. No?

Can anyone shed me some light on what could be the problem?
Greetings
  • 0 over 8 years ago
    The first thing to try is a new battery in the sensor. From what you've said, this is the most likely reason for your problem.

    Next, check the wheel size that the 1000 is using. I always keep the wheel sizes for my in my 800 set manually, since once or twice when I had it set to automatic calibration the 800 screwed up and obtained the wrong wheel size. I have no idea what prompts an Edge to recalibrate the wheel size, but I know they do it on occasion after the initial calibration.
  • 0 over 8 years ago
    The first thing to try is a new battery in the sensor. From what you've said, this is the most likely reason for your problem.

    Next, check the wheel size that the 1000 is using. I always keep the wheel sizes for my in my 800 set manually, since once or twice when I had it set to automatic calibration the 800 screwed up and obtained the wrong wheel size. I have no idea what prompts an Edge to recalibrate the wheel size, but I know they do it on occasion after the initial calibration.


    I tried the battery first thing. So that's not the issue.

    I forgot to mention that part. I had the wheel size on automatic. Once I started to have this problem I set it manual to the correct size according to the Garmin manual. This altered my speed (alot, I was suddenly ride race pace and I'm not a racer). But the issue was still there, I had speed drops on manual aswell as on automatic.
  • 0 over 8 years ago
    Check the alignment of the magnet It should be centered on the line on the speed arm and the gap should be between 2 to 5 mm.
  • 0 over 8 years ago
    If the magnet/sensor spacing isn't correct, wheel/frame flexing can move the magnet out of range of the sensor eg when riding out of the saddle or sprinting.
    This would give you your inconsistent readings.
  • 0 over 8 years ago
    It seems that removing and replacing the magnet seems to have made the difference. Thanks for the help!