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Manly Dam Distance - 9.65 or 10.1
Have been riding with a Garmin Edge 500 for a couple of months now.
Every time I ride Manly Dam I get a distance of 10.1. The Hot Lap lists a distance of 9.65. What's going on.... Am I riding an extra 500 meters, is my Garmin dodgy, or does the trail data need to be updated?
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Doesnt track that well without a sensor I find so that would be the extra distance.
Just not working today... I thought this worked with the gps to provide a more accurate speed / distance calculation?
Does any one get 9.65 consistently with another device?
your cadence sensor is your tacho and would not know what gears your in for wheel revolutions so you need speed sensor for speed and distance.
Yep so that won't help.... Still find it odd that it hits the same distance every ride.
If you take the "A" lines it will be shorter ...
Using a Garmin forerunner 405
I think the hot lap distance was taken from an old GPS trail I recorded. It's not an exact science, if you rode the circuit proper you did the right thing
Happy to update the distance on the hot lap - what's the consensus? </can-of-worms>
That would reset all the hot laps then Rob
I thought the Garmin cadence sensor doubled as the back wheel speed sensor... you just need to place the supplied magnets on both the LH crank and a suitably placed rear wheel spoke. Is that not correct?
@Justin... eh? No reset. Everyone has been riding the main circuit, we all know what that is.
The debate here is just what the precise distance around that known circuit is.
@Rob... nah don't go updating the distance just cause I've raised it. Someone else mentioned they get 9.7 every time so that's close enough.
@Hawkeye... yeah that's what I thought... the cadence sensor has both a crank sensor and a rear wheel sensor... that said though I don't think I had to put any info about my wheel diameter in so how would it know what a 'pass' of the magnet equates to. Will go and have a read of the manual...
I believe it compares the reading it's getting from the rear wheel sensor with GPS distance travelled and calibrates/calculates the wheel diameter
9.65 vs 10.1 is a less than 5% error, so i think you've got to be pretty happy with that actually. Sub-meter accuracy is not possible with uncorrected GPS positions (even when stationary and with a clear shot at the sky, let alone moving and passing under trees). Regarding the additional sensor, if it does calulate wheel circumference/diameter from the GPS reading, then your never going to get an accurate distance as the error in GPS position will get multiplied every rotation of the wheel... Even with a manual input wheel circumference, there will still be some error in the measurement which mutiplied over a ride, could add up to a 'substantial' error.
Sorry for going off topic, I read a guide somewhere for circumference's. I will try and find it.
http://sheldonbrown.com/cyclecomputer-calibratio...
To the previous post, if the unit is clever enough it can calibrate over a long ride, say 20km, which would make 10-20m GPS error insignificant. On my road bike I have a wheel sensor 'puter next to the garmin and they're normally within 100m of each other after 30km which makes roughly 0.3% error
Recently added a gsc10 sensor to a road bike and also defined the additional two bikes. The edge 500 popped up a message after about 5k to say it had auto calibrated that bike. Doubt there will be much GPS variation in 5k.
btw I was also looking at the manual to see if it did auto corrections when GPS reception was poor. There is no setting I could find to turn auto correction on or off so assume its all automatic. I think this means if you have consistent cadence then you have consistent distance.