Garmin says 12.23 miles 49:34:76 moving
Strava app says 12.3 miles 52:44 part of this extra time might be because I had taken jacket off with phone in pocket
Cycle computer says 12.408 49.52

Which is more accurate? Why the differences between the two? Yesterday strava app on iphone and cyclecomputer were about the same.

what do you all think?

The one that's more accurate is the one that you've had certified as being accurate. Nobody does that, of course.

Any consumer lever device is going to vary, depending on a wide variety of factors. GPS units ( standalone and in phones ) have to deal with inherent inaccuracy of several feet most of the time, and occasionally much wider variations depending on factors ranging from satellite position to structures blocking the signal. You can put two GPSs right next to each other, and depending on how their software works they'll give different positions and speeds. Surely if you have a Garmin you've noticed that they often say you're moving at .1-.3mph when you're standing still?

In other words, they're all accurate enough for 99.999999% of the average person's needs.

I have the same problem using 2 Cateye computers. One says I rode .55 miles and the other says 1.01. My MapMyRide app says I rode .7 miles. I trust the app, not the computers. Need something I can trust while on my trainer.

I don't tend to care about absolute accuracy, the same way I don't care if my watch is a minute or so off. What was said about GPS devices is 100% accurate. Heck, going through a dense wooded area or a lot of cloud cover can really throw that off. I would think a properly set up computer that counts wheels revolutions would be the most accurate

The cycle computer needs to be calibrated with wheel circumference to measure distance. Tire pressure can change circumference and your distance. GPS is generally accurate unless you're riding in sheltered areas but they can also have errors. For example most GPS will not be accurate if you're running on a 1/4 mile track. They will underreport distance.

Within about a percent or two is close enough for me.

I'd say it's abundantly clear that the Cateye computers do not have the wheel sizes set correctly...

okay so I think that the computer is calibrated correctly. I just thought it would be a bit closer together. I do know that the Garmin seemed to be quicker at stopping and starting this morning on the commute. I decided to not run the Strava app on my iPhone. (too much of a hassle) I did run it a couple days. The computer and iPhone were pretty close together. I did not expect the Garmin to be that different from computer.

I would say that I am not riding in a sheltered areas. I mean I eventually make it downtown but Downtown here is not like downtown in bigger cities.

I guess I am bit surprised because I was expecting the GPS to be more accurate than my $10 Sette computer and certainly did not like that my route ended up being shorter than I had thought it has been... or is it? haha

The difference between the measurements is so small that it doesn't really matter. Averaging the measurements , you get 12.3 miles as the average with a standard deviation of 0.1 miles. That doesn't mean that the Stava measurement is correct, only that all the measurements fall within a standard deviation from the mean.

Another way to look at it is that there is a 1.6% difference between the high and the low. Not enough to worry about.

A calibrated bicycle computer will always be more accurate than a GPS. The GPS does not account for changes in altitude. It may know your altitude but it doesn't calculate that into distance traveled. The GPS sees the earth similar to a flat map and measures the distance between two points as they would appear on that type of map. The attachment is an exaggerated illustration but I think it conveys the concept.

[MENTION=174997]mmac[/MENTION]h5 that is very interesting.

I think this thread is similar in the questions I am asking

As for the moving time is worth noticing that different devices will stop the timer at different times. My sigma cyclecomputer takes exactly 10 seconds to stop the timer after I came to a complete stop. Bth my Garmin Gps watches stop immediately and thus will yeild a high moving average. Strava running on my phone will have huge variances as sometimes it takes 30 seconds or more to detect that I stopped moving and will lead to a lower moving average as you save the ride. Not uncommon tho to go back to the ride several hours later and see that strava software somewhat corrected the moving time and moving average will be higher .1 or .2 mph on longer rides and even more on shorter rides with lots of stops.

I know that I can change the settings on the GPS in regards to the stop/ start. It can be set to a certain speed and something else I can not remember right now.