Tl;dr

I’m not on a BMX, veering all over to hop curbs and do flatland tricks in the middle of the road (which would be cool, ngl). I’m on my road bike and hugging the shoulder.

what the heck is this:

Definitely was in the road and not bouncing against a building here...


This one here looks like I rode through three neighbor’s lawns then, like Wile E Coyote, smashed through four of their houses and rampaging a lap and a half around inside the fourth one before blasting out their bay window and resuming my way North on Oswego...


I’m only using my iPhone instead of a dedicated GPS unit. I found a few threads that mentioned some discrepancies regardless of phone or DGPSU, but is this really what’s going on for everybody or have I dropped my phone too many times?


~~~~~


I wouldn’t have noticed this if I didn’t loose huge chunks of today’s ride where I was dead certain that I’d Top5’d a segment... but it’s gone along with the first two miles of my ride, but I magically avg’d 25mph.

Because of what it was telling me, I thought my cheapo Cateye Padrone computer was off so I went and enlarged my wheel setting in hopes of getting more accurate readings on my handlebars.

I'm surprised Strava didn't smooth that out for you. You did specify bike rides, and not a walk or a run, right? A cycling GPS would smooth that right out, and probably keep you on the street (although that's less certain).

Anyhow, your tracks are a great illustration of why you'll get better accuracy with a well-calibrated wheel sensor than with a GPS.

Were you always moving? If so were you always moving fairly fast?

I can imagine that in areas of poor gps reception that it might have thought you were standing still sometimes. As for the track being off the road that you obviously rode on, well that's normal for any gps that is plotting your actual position that it thinks you are at.

Nuvi's and other auto GPS's snap your route to the nearest road going in the direction you are traveling. So they just lie outright about where you are. And that makes us falsely believe they are accurate.

Were you dodging dogs and pedestrians?

Possibly bad gps reception due to buildings, obstructions on your bike (like your head maybe), or trees. GPS relies on the time difference in the signal it gets from various satellites, so if a couple of them are dropping out regularly that causes the location to be off.

while drunk maybe (G)

it's the OP's word against the documentary evidence.

GPS signal can be erroneous especially in urban valleys (after all, it was designed to get missiles to hit the right spot in less dense environments that you'd expect have strategic value, not the corner coffee shop downtown across from the other coffee shop that you don't want to take out).

Your phone GPS could also be messed up, either software or hardware. I know I've had phones that needed rebooting to properly acquire more accurate coordinates. I've also read accounts of people whose GPS antenna broke or were faulty, usually a manufacturing flaw making them flimsier than you'd expect.

Also, nothing could be wrong other than you started moving before it locked on to enough satellites to give you better accuracy. Happened a lot with my Garmin Edge 520, if I started moving before it acquired a lock, it'd trace a drunken trajectory as it made a best effort to guess without enough signals.

Yeah, it’s always left on bike-mode. How does one go about calibrating a wheel sensor?

I was kinda using Strava to calibrate my Padrone computer, I thought. I guess I should reset the Padrone back to the appropriate tire circumference and just trust it over Strava?

You got me. My breakfast is typically steel cut oatmeal washed down with a bottle and a half of Winking Owl. I probably could cut it back to just one bottle, then I’d have two whole bottles left over for lunch!

It’s relatively flat on this route, and although the first two screenshots are of an area with a 200-300 foot (?) hill/ridge bordering one side there’s tons of cell and two-way radio towers all around town... the third screenshot is right near a lake and it is f l a t for a seven mile radius.

It seems very probable that my over-app’d, old, beaten-to-heck phone would benefit from having all unused apps shut down and do a full reboot before setting out on the recorded rides.

Thanks, folks!

Re: bike mode, looking at your original plot I wondered if your phone was on walking mode -- like when you're talking friends on the phone outside the bar and walking back and forth. As opposed to driving directions, when it figures you're on the road or street and fits location to the road.

I'd reset the Padrone until you can get to a good calibration road: road that's straight and flat without traffic signals or stop signs, and (the tough part) one with accurately surveyed mile markers. Note your starting mileage on the Padrone and the mile marker, ride as far as you can, and note stopping mileage (Padrone and mile marker). Figure your correction (mile marker distance * current wheel circumference / Padrone distance) and put that in as your new wheel circumference.

(Hope I got that straight!)

Yeah, that's not unusual, whether with a phone or GPS computer. I usually run both my phone and bike computer and it's not unusual for one or both to have a jittery, jagged trace some days. Seems to depend on weather, surroundings (there are a couple of segments along my usual route where GPS loses sync for a few hundred yards), moon phase and how much turmeric and essential oils Gaia sprinkled on the ozone layer.

Usually Strava does some smoothing. I usually record to Wahoo Fitness on my phone, then upload to Strava, and the data and GPS trace will differ slightly. Ditto, my bike computer's native app and Strava. My computer supposedly uses all or most global positioning systems (GPS, Glonass, Beidou) and switches automagically to whichever has the best signal, but there's no way for the user to determine that. I suspect it defaults to the primary system for our region.

Also, most phones can use cell tower data as a backup when GPS sync fails. I don't know whether there's any bike computer that can do that. This may explain the occasional significant variations I see between my phone and bike computer logs.

On good days when I get a solid locks and the GPS trace is smooth, I can see every segment where I change lanes, backtrack for a few yards to check out something interesting along the roadside and snap a photo, etc. Other days the GPS trace is so ragged it's very approximate. And it loses sync as soon as I step inside my apartment complex, so if I forget to end my ride/run before entering the building I have to use the crop feature to avoid nonsense data indicating I "rode" a mile of loops inside my building.

its weak GPS. I get all the time try riding in a parking deck it gets really crazy or if you leave GPS on and stop at store.

It is "normal" in certain areas because the GPS can be inaccurate due to local conditions. I have a route where I'll see that about half the time. Other times it's not so pronounced, but still fluctuates for the overall distance. It also varies per GPS device - some are worse than others. I use a wired wheel-sensor computer for accurate data, and the GPS more for navigation and Strava features.

GPS is much, much more accurate than the location from cell towers.

GPS takes a while to get accurate location. Starting with a good approximate location allows GPS to start up much quicker.

Often, the location is needed on phones much quicker than GPS can get it. That's another reason cell towers are used. Phones can also use databases of WiFi networks to get location. Both these (cell towers and WiFi) also work better indoors.

I get errors like these very often. They are common when cloud cover is thick. They are even more common in the city with tall buildings and radio interference. Sometimes the GPS has me darting in a weird direction and back at a speed of 50 mph. Sometimes it shows me going through buildings or riding on the river, things we know I didn't do.

But you were working in IT, right? I thought all IT people could at least walk on water.

Yes I worked in IT (I'm a student again now) and yes, we walk on water, but we don't cycle on water. Surface tension can't sustain the tire pressure.