Related
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Distance, speed - calculation method

adiik
over 3 years ago

I cycle with my wife, I have an Edge 1030, and my wife has an Edge 1000. We both have speed sensors manually configured for the same wheel size, of course we have the same wheels and tires. Always Edge 1000 shows a route shorter by about 1.1%. For example, today the Edge 1030 showed 51.23 km, and the Edge 1000 showed 50.68 km.


1. Is the total distance calculated from the GPS track record or from the reported wheel rotation from the sensor?
2. On what basis is the average speed, maximum speed calculated? Wheel rotation or GPS data?

I exported both routes and got these results on trackreport.net:

Edge 1030:

Garmin Connect trackreport.net
Distance 51,23 km 51.53 km
Max speed 58,7 km/h 59.28 km/h
Avg speed 31,2 km/h 31,40 km/h

Edge 1000:

Garmin Connect trackreport.net
Distance 50,68 km 51.43 km
Max speed 50,2 km/h 51.84 km/h
Avg speed 30,0 km/h 30,44 km/h

As you can see, the length of the GPS track given by trackreport.net is almost identical, the difference is only in Garmin Connect.

  • 0 over 3 years ago

    Given the fact that the difference between your wife's distance is constant my guess is that one of your wheel sizes is nor set correctly. The fact that they are the same number does not mean it is correct. Tire type, pressure and weight does matter. Whether the wheel size or GPS is used to calculate the distance is easily tested by putting in a ridiculous wheel size on one of your units. My guess is that the sensor is used to calculate the speed and distance.

  • 0 over 3 years ago in reply to lhol

    If you have a speed sensor paired then that will take priority over the GPS data in terms of the unit computing speed/distance.

    Things to check are whether the speed sensor wheel size is set to manual or automatic. If it is set to automatic then the unit is constantly re-computing what the wheel size value is and adjusting it using a slow moving average.

    If it is set to manual then teh value is static, but needs to be correctly set.

  • 0 over 3 years ago in reply to aweatherall

    So if a speed sensor is connected, all distance and speed data is calculated from the speed sensor data? If so, this is probably why my and my wife's Edge reports different distance (different weight and tire pressure).

    As I wrote, the size is set manually. Also, to avoid the influence of pressure and weight fluctuations, it is better to set the wheel size to automatic.

  • 0 over 3 years ago in reply to adiik

    My own personal preference is to set the wheel size manually, but to determine wheel size by doing a rollout with the rider on the bike.

    Here are a couple of methods

    Wall Roll

    • Sit on your bike next to a wall.
    • Roll forward till your valve stem is at the bottom of the wheel.
    • Have a friend mark that spot with tape of chalk.
    • Roll forward one revolution of the wheel so the valve stem is at the bottom of the wheel again.
    • Mark that spot with tape of chalk.
    • Measure the distance between the two marks in mm. That's your number!

    Paint or Water Roll

    • Put a blob of wet paint or water on the pavement.
    • Ride over it and keep riding.
    • Each time your tire hits the pavement again, it should leave a mark.
    • You should be able to measure the distance between marks (or between multiple marks for even greater accuracy).
    • Measure that distance in mm. That's your number!
  • 0 over 3 years ago in reply to aweatherall

    I use a third method:
    I watch the difference between GPS distance and sensor distance for several activities. (No forest trails - only cycling trails in open terrain.) I calculate the deviation. In your case, for example, 50.7 to 51.4 km. That is 2% deviation. I average these deviations and then set the bike circumference larger/smaller by this amount.

    Still to be mentioned:
    I don't care about 1 or 2%.

  • 0 over 3 years ago in reply to aweatherall

    I used very similar method, but with sticky notes. 

    As you can see, I only measured the wheel size for my bike, I set the same value on my wife's edge because she has the same wheel and the same tire, but it was a wrong assumption. I measured the distance on an unloaded bike and it is 2 centimeters longer, so the weight of the rider and the pressure in the tire play a big role.

    However, I will set it to the automatic and see what values I will have after the next ride.

    Anyway, I got the answer to my question: all distance and speed data are based on the speed sensor (if connected) and ignore GPS.