GPS distance measured on a 26in vs 29in bike different?

[Jewbacca]

3 hours ago, 117 said:

 

Without getting toooooo technical, elevation is based on barometric pressure. Strava's absolute elevation measurements are previous recordings of elevation averaged out 

If your phone has a GPS receiver, it should also have a barometic sensor too but here I'll go on what the manufacturer says. 

hahaha yes. Sorry, I misread your post originally. 

Cumulative data based on harvested historical activities.

One can choose to use this method regardless as it tends to be more accurate than a single time Baro recording.

Anyway, I have no dog in this fight. The basemaps data is really accurate on well ridden/travelled paths and roads and is worth using. 

Edited December 10, 2021 by Jewbacca

[RobbyB]

8 hours ago, Battery_Chick said:

No speed sensor, just GPS. It was a good line of thinking though 

If you do get a speed sensor then the best way to work out your tyre circumference is to place a bit of tape underneath your tyre (on the wheel with the sensor on it). Make a mark on the floor (next to the tape when the tape is positioned directly underneath the wheel axle), get on the bike and ride for one wheel revolution (down a passage for example), get off the bike and make another mark (next to the tape when the tape is positioned directly underneath the wheel axle). The distance between the two marks is an accurate measure of the circumference of your wheel as to when you are riding on your bike. Sounds complicated but it's pretty simple to do and it's essential  for accurate speed/distance measurement.

(A milestone in Posts...🔞)

Edited December 10, 2021 by RobbyB
Added info...

[117]

Um.... It's easier (and more accurate) to simply multiply the diameter by Pi. By using a measuring tape around the wheel will actually yield a different result as the tape measure is not compensating for the curvature. Symantics I know

Thus: 29 x 3.14159 = 91.10611" x 2.54 = 231.409cm

Here endth thy mathematics lesson

 

[Jaco Steyn]

18 hours ago, 117 said:

Michelle, the ruskies repositioned one of their birds and this is giving a new position to your GPS receiver, giving you 1.3% difference. It's basically the conversion between imperial back to metric. 

Just kidding, wheel sizes has nothing to do with it. It's the time interval between GPS spots which might cut a corner between the spots, hence giving a shorter distance perception. If you can set the GPS to record every second (make a spot every second I mean) and do a few rides on each bike you'll find it'll be the same distances

I once had two Garmin cycling computers on my road bike to compare the distance measured to each other. One on an out-front mount(New Edge 130) and the other (Old Edge 500) on the handlebar. After a ±50km ride, they differed also about 1.5%, but it did not bother me because it probably is within acceptable margins of error. But then my OCD kicked in and researched a bit. I then made sure that both were set to do per second recording and not smart recording. Since doing that they are both measuring within about 0.25% of each other. 

[Eldron]

1 hour ago, 117 said:

Um.... It's easier (and more accurate) to simply multiply the diameter by Pi. By using a measuring tape around the wheel will actually yield a different result as the tape measure is not compensating for the curvature. Symantics I know

Thus: 29 x 3.14159 = 91.10611" x 2.54 = 231.409cm

Here endth thy mathematics lesson

 

It's even more accurate to make a mark on the tyre, jump on the bike, roll one revolution then measure the distance.

The PiD formula doesn't account for varying tyre size and the various shapes those varying tyres make when on different width rims.

[The Habrador]

Try measure the loop with Strava on your phone a few times and you will see the (huge) variation that can happen. A Garmin is significantly more accurate (i.e. has a faster polling internal) than strava on your phone, but you'll get the idea that a 150m variation over a 15km loop is actually pretty accurate. Also, there is a fair amount of "distortion" that happens (mostly on measurement of elevations rather than distance) due, as far as I know, to the more extreme angle of sight from SA to GPS satellites, which are skewed towards providing service to the northern hemisphere (unvarified info!).

[117]

It does account for varying tyre sizes, you then use the C=2(pi)*r formula 

No need to reinvent the wheel, scuz the pun

56 minutes ago, Eldron said:

It's even more accurate to make a mark on the tyre, jump on the bike, roll one revolution then measure the distance.

The PiD formula doesn't account for varying tyre size and the various shapes those varying tyres make when on different width rims.

 

[Jewbacca]

hahahaha I love the pettiness all for R200m at most. 

This is solid internetting

[Eldron]

3 minutes ago, 117 said:

It does account for varying tyre sizes, you then use the C=2(pi)*r formula 

No need to reinvent the wheel, scuz the pun

 

That is the same formula as Pi*D

I figure if you're going to go to the trouble of measuring the actual diameter of the wheel then geek out properly and do the roll out test and get exactly the right answer....

[100Tours]

I have found that if you start your ride with the Garmin in your back pocket, and then move it up to the handlebars while riding then you can gain free distance. You can also do this on your favourite segment to improve your time.

The benefits are maximised if you use an out front mount.

 Marginal Gains. 👽

EDIT: if you want free vertical m's then you should mount the GPS on your shoe 💯

Edited December 11, 2021 by 100Tours

[Oodles]

1 hour ago, 117 said:

It does account for varying tyre sizes, you then use the C=2(pi)*r formula 

No need to reinvent the wheel, scuz the pun

 

It doesn't account for tyre pressure as the diameter changes depending on the tyre pressure 😀

[SwissVan]

6 hours ago, 117 said:

Um.... It's easier (and more accurate) to simply multiply the diameter by Pi. By using a measuring tape around the wheel will actually yield a different result as the tape measure is not compensating for the curvature. Symantics I know

Thus: 29 x 3.14159 = 91.10611" x 2.54 = 231.409cm

Here endth thy mathematics lesson

 

But Pi x D does not take into account the tyre flex due to weight on the wheel  😁

 

Edit: Sorry late to the party see Eldron beat me to it

Edited December 11, 2021 by SwissVan

[SwissVan]

3 hours ago, Jewbacca said:

hahahaha I love the pettiness all for R200m at most. 

This is solid internetting

"Just do it"..... famous quote 

[117]

25 minutes ago, SwissVan said:

But Pi x D does not take into account the tyre flex due to weight on the wheel  😁

 

Edit: Sorry late to the party see Eldron beat me to it

The flexing tyre is not blue toothed to the GPS to transmit its ever changing circumference either....

Geeked out 👋🏻