JackieYan

I use two apps: Strava and Map My Ride. I also have a Cateye CC-MC200W.

I'm interested in finding out why there's a small discrepancy on the distance the three units record.
For example today on a ride I saw the following distances:
Cateye 32.8km
Strava 33.45
Map My Ride 33.05
As the two Apps both use GPS, I would have thought the distance would be exactly the same, although I know it's only around 1 2-%.
Sometime my Cateye records slightly higher kilometres than the two Apps, so it's not always consistent.

Can anyone enlighten me?

canklecat

This comes up a few times a month. It's "normal," if by normal we mean common.

It's due in part to GPS sampling, how the apps use the data, and, with Strava, how they interpolate data and blenderize it with their own secret sauce.

Weather may be a factor too. There was some glitch Monday that dropped the first 15 miles of my 50 mile ride, using my bike computer. But my phone app logged the entire trip. However the average speeds, etc., were wildly different. That glitch seems to occur pretty often in the same area, so it may be radio frequency interference or EMI, or might be due to the shallow valley in that route, surrounded by adjacent hills, tree cover, etc.

It also depends on how the device or app uses auto-pause/resume. Some have an adjustable threshold, which may help with interruptions for traffic lights or stop signs for cyclists who slow roll, then accelerate. Others have a preset, non-adjustable threshold for auto-pause/resume, and our times, speeds and distances will differ.

If you watch some videos of cyclists tackling Strava segments, they'll often manually start and stop their computers, rather than relying on GPS for designated begin/end points to automatically mark their efforts. I'm not sure it's any more valid for the cyclist to start/stop computers, since it's bound to vary slightly from the actual begin/end points.

A wired computer, properly programmed for wheel diameter, etc., will probably give you the most accurate data, followed by wireless. My various Bluetooth and ANT+ sensors glitch occasionally, presumably due to RFI/EMI, so those aren't 100% accurate either.

Ditto GPS based estimates for speed and distance. Glitches can occur. Strava and some apps attempt to correct minor glitches when GPS sync is lost, and will try to correct the route trace by guesstimating our most likely route based on where we were when GPS sync was lost and reacquired.

Before getting a dedicated bike computer with GPS and compatibility with my various ANT+ and Bluetooth sensors, I'd occasionally carry an iPhone, an Android phone and run 2 or 3 apps to compare data. They always differed slightly.

After getting a bike computer I still run Strava or Wahoo Fitness to compare results. They always differ a bit from the bike computer's numbers using various sensors.

I'll worry about it if I'm ever fast enough to contend for a significant KOM. I've had a few top tens but those personal best times were still pretty remote from the KOMs, so minor discrepancies in my speed/time weren't significant.

jpescatore

Agree with canklecat plus: in addition to biking, I also hike once a week with a friend and until recently we would both use MapMyHike app on our Android phones. The same app on the same OS, but different phone hardware, would record different distances for the two of us, often as much as .25 - .5 mile difference on a 6 mile hike - even when we purposely started and stopped the app at the exact same times.

Under Armour pulled MapMyHike from Android, I've been trying to use Strava for hiking but found it very buggy for that, will probably try MapMyWalk which UnderArmour seems to still support on Android.

JackieYan

While I realise the two Apps can be set for auto-pause at traffic lights, I'd guessed that was more useful for timing the whole journey, etc.
I had assumed (dangerous, I know), that purely for logging distance, (which I wanted to do today to compare the three) that it might be more accurate.
Not a problem at all, I was interested to know why there was a difference.

Interesting replies, especially about the difference when using the same App on two different phones.

This is my first post, As a novice, I hope to find out more on the forum in the future.
Thanks a lot.

sharktrack

It might also just be how the operating system handles background apps. It could give priority to one or the other and lower the GPS sampling rate for the less-preferred app

hcgaloi

My mistake was I entered 28mm tire size in one unit and 25mm on another one. Thus, there was a slight differences in total distances until I figured it out.

Good luck