Today’s ride was to calibrate and compare data from different sources.
I rode a set course twice. First was with a Garmin FR910XT with GPS set to off. Mileage was determined by the GSC10 speed/cadence sensor. I also had Strava Cycling and Map My Ride apps running on my phone (Android SGS3 if that matters to you). Second time was GPS set to on, and speed sensor off. And both phone apps running again.
I started at a fixed road marker and took measurements as I hit each mile marker on the road.
DISCLAIMERS: I know highway mile markers are not going to be dead on accurate. Intersections, driveways, etc…may warrant that they be placed somewhere less than exact. As for bike sensors with spoke magnets, certain factors will affect there accuracy as well. I ran a 700x28c tire at 110 psi and a circumference setting of 2136 on the computer. Now air pressure in the tires and my 230 lb carcass sitting on the bike seat may affect that a wee bit. And finally, GPS can be affected by buildings, cloud cover, etc. There weren’t any buildings, or trees on this route that would have affected me, but the sky was a bit on the overcast side. (that being said, the Garmin GPS was pretty damned accurate to the markers. And please note that Strava only measures in tenths).
In the chart below, 0.00 was obviously my start and end point. There was no actual mile basis for this. Just a highway marker that I could use as a “start/finish” line. Under “Segments”, 1 was when I hit the 9 mile marker almost right away. 2 was at 9.5m, 3 was 10m 4,5 and 6 were at 11,12 and 13 mile markers. At that point I turned around and took measurements again.
On the first lap, I missed recording the 9mi marker as it was at a sketchy intersection and unwise to stop. I should note that on this first route, I stopped at each marker and logged everything manually on a sheet of paper I kept stuffed in the leg of my bike shorts.
In looking at the chart below, the manual readings are the running total of mileage I was recording from the GSC10, MMR1 and Starva1. The data from FR910XT was taken on the second route, and I utilized the “lap” button on the watch to gather that information. I did not bother to stop at each marker this time, which is why there is no information under MMR2 or Strava2 except for the total at the bottom.
The bottom part of the chart was the mileage as recorded by the Garmin GPS. For MMR and Strava, I just did the math to get the numbers.
Elevation gain and loss is from the Garmin. Not sure if it was GPS based, or based on the barometric altimeter of the unit.
And finally, at the bottom of the chart, I calculated projected mileage if this were to be a 100 mile course, as I am involved in route planning for http://www.paradiseridekauai.com/ And we ant to provide informatio0n that is as accurate as possible for the riders. Especially on the Century ride part, because where cyclists are concerned, if you advertise 100 miles, you damn well better have 100 miles. And let me tell you, that is no easy feat when you live on island that is only 560 square miles and only has approximately 120 miles of roadways that are not residential neighborhoods.
Now that I can see how well this all works (or seems to) I will be compiling route sheets for PRK for all three routes: Saturday’s 50 mile east side ride, Sundays 50 mile ride and Sunday’s Century.
Below are links to my Strava, Map My Ride and Garmin profiles if you’re interested in seeing more data. I have to say, Garmin is awesome and provides a wealth of information.