Meh. I have a route I ride frequently. My GPS ride tracker gives me a normal distance of 7.8 miles, backed up by my wired computer, but I've seen that same route read 7.6 and 8.0 miles ON THE SAME DAY. I've had times where I've turned the thing on, it gets a lock on a better satellite after it is already recording, and I've got 500 feet on my ride before I've even moved. I use it for generalizations, not precision measurement.

Proof (I think these are public, let me know if not):

Outbound leg: https://www.strava.com/activities/562620278
Inbound leg of the exact same ride, same start/end: https://www.strava.com/activities/562620368

EDIT: And a normal leg over that same route: https://www.strava.com/activities/562614792

To the OP, I have no idea how easy it is to modify GPX tracks (I'd imagine not all that difficult), but I'd be as surprised (or care) as much as when someone knocks a couple strokes off their golf card.

The resolution on your GPS unit is terrible.

On rides of 30+ miles, my wife and I have had end results of the exact same distance and elevation multiple times, and the greatest variance has been ~0.25 miles between the two of us. Garmin 500 and 520, respectively.

We don't seem to have a digital doping problem around here. A whole lot of people leaving their app running on the freeway, though. A lot.

Possibly is. Or slow at picking up satellites. Or affected by dense tree cover. Or bogged down processing things besides my GPS tracker. Or any number of things. It is a cheap cell phone I bought unlocked for $30, but for what I really need the GPS for, it works far better than my needs.

My point being, handheld consumer electronics with GPS units are hardly calibrated, precise instruments that you can rely on for racing type timing results. Even your worst case distance difference is proof that one can have the discrepancy the OP was worried about.

And I have the opposite problem: I leave my app running when I am walking around, making myself look even slower than I actually am :)

This is the right answer.

I have a Garmin GPS watch for hiking and running and swimming, and also an Edge computer. My experience is pretty much like yours. I have to go about 30 miles before they disagree by 1/10th mile.

We have plenty of dense tree cover in the Pacific Northwet. A good GPS (not yours apparently) is fine with dense tree cover at cycling speeds. It's a problem hiking because the speed is so much less but the speed you carry on a bike (really the inertia that comes with that speed) rules out 90 % of the jitter in the signal.

You want it to Lie to you in a way that makes you feel better about your self.

This seems like a really stupid way to change values in files. A simple bash script could increase your speed by X% SMOOTHLY and simultaneously reduce the time with some quick math. What the heck stupid program are these people using to "digital dope?"

Oh, as for the OP. Who cares?

No idea what people are using.

To be blunt, I have one person on the leaderboard I'm competing with... the Hypno Toad.

Strange thing happened to me the other day. I was riding with my wife, we both run Strava, on our normal 20 mile loop. We always end up at 20 miles on Strava on this loop, so this was very strange to me. She ended up at 20 miles like normal at a 13.9 mph pace (slow day). My Strava showed 18.8 miles at a 15.2 mph average. The Strava map indicates the same exact turn around point and even grouped us together, but there was still the massive discrepancy. I say its on the fritz!

Good for you. Do we know the OP's nemesis was using a "good" GPS? I merely gave real life examples where consumer electronics gave bad readings, as proof it can and does happen.

By all means, if it makes you feel good that your couple hundred dollar GPS watch works better than my $30 phone, feel free to continue mentioning that. I'll fully admit that it is not a top of the line piece of electronics. That said, many people use phones as their tracking device, and I have little doubt that any GPS or software controlling it in a phone is prone to errors from time to time.

Anybody know how Strava uses and records time? I've had the time off on my android phone by quite a bit, and it all seems to work out just fine. But, would other devices be more sensitive to the proper time? Having the time off by a minute or two could give a bizarre "flyby" summary, but really wouldn't affect the overall ride at all.

You told us consumer-level GPS can't provide any realistic measure of accuracy. I demonstrated that it's not true. That's all. No need to get so offended, we're just talking about how stuff works here.

I've actually seen one where it appeared someone left their app running while flying across the country.

OP and some people's expectations of what you can get out of consumer devices is unrealistic. Expecting every source to match even more so.

In the example above, if you assume one of your devices was 100% correct, then the other one was about 99.67% correct. But that is assuming you and your wife rode the exact same track which is unlikely. If you go wide on 10 corners, that could account for a 500 foot difference. Even so, if I got slightly different numbers from 2 units on my handlebars, I wouldn't worry about it. We used to ride with little wheels that ran off the tire to measure miles to the nearest 10th. So a Garmin is magic* in comparison.

Most cell phones seem to use the time broadcast by the provider. In the past, I found that at&t was off from the real time, but that doesn't seem to be the case anymore.

The time on any real GPS unit is going to be correct to the second (actually a lot less, it's critical to how they work.) Cell phones have GPS chips in them, but I can't see that they're used to set the clock.


*Any sufficiently advanced technology is indistinguishable from magic. -Arthur C. Clarke

According to the UCI, Union de Cyclisme Imaginaire the world governing body of Imaginary Racing, the only verifiable results are the ones that you like best.
As UCI Commissar Captain Fast explains:

"Imaginary racing is dubious, arbitrary and shot through with both intentional and accidental errors in speed, timing, distance, finishing order, elevation gained/lost and even calendar date.
This in no way prevents it from being the perfect platform for preening, boasting and making exaggerated claims in anti-social media."

Altering strava data is not doping and threatening others with litigation. Come on now. I wouldn't even call that bullying, get real. Half of the OP was about how much better he is than his fellow riders; I would consider that as bad a faking strava numbers.

And I provided examples where they didn't. I'm hardly offended, never said that they couldn't provide good results (and in fact, stated that for most needs, even ones that don't work that well are more than accurate enough), just that to expect that because it is ultra-accurate satellite based it can never be off is silly.

FWIW, my $10 cycle computers and my $30 cell phone are generally within 1% of each other, and rarely more than 1.5% off, far better than any accuracy I actually need in real life. That does not mean they cannot differ substantially, and differ from my expectations on known courses, though.

OP rides a Velocraft NoCom.

Not sure if he rode it on this particular ride but very few diamond frame riders could keep up with a reasonably fit rider on that thing.


-Tim-

I think Hypno Toad is on to something here.

Also, just because you were ahead of him on the segment in real life, doesn't mean he didn't do it faster than you. You stated yourself, you were two miles ahead and soft pedaling. So you soft pedaled a segment at 15mph, he did it at 20mph...you were still two miles in front of him, but he was faster on the segment.

I have this happen plenty in a paceline where someone behind me went faster than I did on a segment.

Could be (?) the frequency that your phone is transmitting your location data out? I'm making this up, but conceivably if your phone does it every 20 seconds, and the other rider's phone does it every 5 seconds, what would be the effect?

My thought was that if he'd somehow set the clock on his Garmin to a minute ahead, it would look like what I saw. But I thought they get their time signal from the satellite? Anyway, to restate the problem, in real life sometimes he led during the ride and sometimes I did; but the flyby showed him in the lead all the time. There were no KOMs involved.

If you're both using Garmin, the time-stamp should be the same (give or take 40 ns) . However, if the other rider is using a phone app, the time may be off on the phone. I do not have any experience with this issue, just putting the idea out there.

Good point. It doesn't have to transmit during the ride, but there is a sampling rate and I noticed on one of my phones that every segment time was rounded to the nearest 5 seconds. I don't know if that was up to 5 seconds rounded down, or two and a half seconds up or down, but at 30 feet per second or more that's a lot of variable distance.

I don't expect more than 5-8 meters accuracy from a cell phone anyway (they have cheap receivers) so it won't be accurate for who's ahead of who regardless.

Yup. Strava is wrong.