# Speed board/ski apps inaccurate? why?



## SnowDragon (Apr 23, 2012)

Just finished reading the same thread on helmets and was gonna start this thread as well.
So why are ski tracking apps not accurate? (I haven't used one yet...)


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## Banjo (Jan 29, 2013)

I am interested in this claim as well. After the first thred of "they dont work" i turned it on and drove back from Golden. Tracked my speed in my car almost spot on climbing hills, going down hills, correct elevation etc.


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## Board Gadget (Oct 30, 2012)

Me too. I tested mine in a car also. Alpine Relay and DotFreeRide.


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## kungfulu (Jan 4, 2013)

It has to do with how they clock or log latitude and longitude coordinates. The more it logs GPS the more accurate the app. So, for an example, it pings every second it collects less data vs collecting every half a second. It tracks the GPS changes. So if I am in spot A and spot A has Long/Lat of this, when I am on B it has Long/Lat this. It tracks the time from A-B and it gives your speed. So when it pings the GPS this second on A and the next second it pings and you are B, it calculates it took 1 second to go from A-B so this is your speed. Now take the same example but use the half a second ping and it is way more accurate. So you ask why are the apps not all using the half second vs the 1 second? Battery. For a true accurate reading it would have to be a constant ping and that would kill your phone very quickly on battery.

Edit: I also forgot to add new or old phone or even what kind of phone. Older phones use older GPS chips. It boils down to how accurate (with-in feet) the GPS chip tracks. Older phones (or older chips) have less accurate tracking. You hear some GPS can find something within 10 feet. That would be less accurate of one that could track to 1 foot. Some are less some are more. The less distance of tracking the more accurate.


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## chomps1211 (Mar 30, 2011)

kungfulu said:


> It has to do with how they clock or log latitude and longitude coordinates. ... an example, it pings every second it collects less data vs collecting every half a second.
> 
> ... So you ask why are the apps not all using the half second vs the 1 second? Battery. For a true accurate reading it would have to be a constant ping and that would kill your phone very quickly on battery.


Ok, I get all that. As I mentioned in op, I never took any reading of my max. speed to b 100% spot on. I always assumed that any logged speed would likely b +\- a few mph. So I suppose the argument being made by detractors of these apps. Are the flat out claims of top speed without acknowledging THAT discrepancy?

Or are people claiming that these apps. are unreliable and inconsitantly inaccurate enough that ANY given speed is questionable?
Additionally, that still doesn't address my observation that similar apps used when I ride my MTB seem to B reasonably close to the milage & mph's logged with my bike mounted odometer! Again, usually anywhere within 3-5 mph. Any time I've encountered larger variences than that, they can usually b traced to signal loss or interference. 

That level of accuracy is good enough for me to be reasonably confidant that I'm not making wildly inflated, bullshit claims for my snowboarding speeds. Are we arguing about split hairs here? :dunno:


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## kungfulu (Jan 4, 2013)

chomps1211 said:


> Ok, I get all that. As I mentioned in op, I never took any reading of my max. speed to b 100% spot on. I always assumed that any logged speed would likely b +\- a few mph. So I suppose the argument being made by detractors of these apps. Are the flat out claims of top speed without acknowledging THAT discrepancy?
> 
> Or are people claiming that these apps. are unreliable and inconsitantly inaccurate enough that ANY given speed is questionable?
> Additionally, that still doesn't address my observation that similar apps used when I ride my MTB seem to B reasonably close to the milage & mph's logged with my bike mounted odometer! Again, usually anywhere within 3-5 mph. Any time I've encountered larger variences than that, they can usually b traced to signal loss or interference.
> ...


I don't think they are inconsistently inaccurate. I think they are consistently accurate for how it is being logged. To your point of signal drop...that could be a huge factor in the results, solar flares can alter GPS readings…the list goes on. Even a half a second drop of not logging would throw the math off of how these track and would change the +/- big time. Each app creator uses a different algorithm based off of how they are tracking and how they built the app. You could take 3 different apps, load them on 3 iPhones and throw all three in a backpack, bomb down the mountain and when you pulled them out, they would probably all have a different number. The closest you could get to the real number is using the same app on the same phone over and over and that is because it would use the same way of collecting over and over.


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## poutanen (Dec 22, 2011)

I tracked myself with apps for a couple years, various apps and various phones. My top speeds (after correction) were consistently anywhere from 100-130 kph each day.

I bought a Garmin GPS watch this year (after losing a phone on the hill) and was expecting similar results. My boarding hasn't changed, in fact I'm likely going FASTER as I'm used to the mountains more this year, but the top speeds have gone down to the 70 kph range at Fernie and Lake Louise (more off piste), and the mid-80 kph range at Nakiska (groomer bombing/hard carving).

The other thing is, my max speeds used to fluctuate by 20 kph a day at the same hills. Now it's very consistent. All my max speeds since changing to the watch (about 30 on hill days ago) have been within approx 15 kph over ALL the hills.

Next time I'm out, I'll take a smartphone with the app and run the GPS watch at the same time.

Overall distance will be reasonably close, although the apps don't pick up carving. Max speed for the day is just so random that looking at an app and saying things like "my max speed is higher than yours because _____" just doesn't make sense.

The apps are fun, it's a great way to push yourself for longer distance and vert each day, just ignore the max speed readout. It shouldn't even be there...


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## chomps1211 (Mar 30, 2011)

Poutanen, just curious which GPS watch you are using and do you know how it is logging coordinates? 1 sec. or 1/2 sec. intervals. Or do dedicated GPS receivers handle things entirely different than phone app GPS does?

Looking to school my ignorance here,..


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## poutanen (Dec 22, 2011)

chomps1211 said:


> Poutanen, just curious which GPS watch you are using and do you know how it is logging coordinates? 1 sec. or 1/2 sec. intervals. Or do dedicated GPS receivers handle things entirely different than phone app GPS does?
> 
> Looking to school my ignorance here,..


It's a Garmin Forerunner 410, and it doesn't have a set interval for logging. They claim it has a "smart interval" that decides when to log based on calculations.

From what I've read, the intervals can be anywhere from 1/2 a second to 5 seconds or so.

For what it's worth, the apps I used recorded raw GPS data from the phone at intervals that I told it to, and I uploaded that data to Garmins website, so I'm comparing apples to apples as far as how the data is interpreted after it's recorded.


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## AcroPhile (Dec 3, 2010)

Me, a few buddies, and the gf all have have the same Ski Tracks app. I have an iPhone 5. One of my friends has an android phone and the gf has an iPhone 4. Whenever we all start our apps at the same time and ride together all day and then check our stats at the end of the day we all get different results. 

The gf's iPhone 4 is the worst offender. It consistently reads faster and steeper than anyone else's stats. There are days when we all cruise at the same speed all day and ride the same runs then when we check the stats, the gf's phone usually records speeds 5-15 mph faster than all the other phones. One day she had a maximum slope angle of 54 degrees when I'm sure we didn't exceed 30. 

I take these ski tracker app stats with a grain of salt. Whenever I achieve a new top speed I'm always skeptical.


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## Deacon (Mar 2, 2013)

I guess I mostly just use it to compare one day to the next, not one rider to the next. And for that, it works. Plus it scares my wife, so that's fun!


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## AcroPhile (Dec 3, 2010)

The Deacon said:


> I guess I mostly just use it to compare one day to the next, not one rider to the next. And for that, it works. Plus it scares my wife, so that's fun!


I think even then it may be inaccurate. I think that at times it looses gps reception and that's when some of the stat keeping goes haywire. Sometimes I look over my GPS tracking it shows that I rode a straight line down a trail when I know I was deep in the trees in between two trails.

Accuracy probably depends on the terrain that you are riding.


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## Lamps (Sep 3, 2011)

chomps1211 said:


> Ok, I get all that. As I mentioned in op, I never took any reading of my max. speed to b 100% spot on. I always assumed that any logged speed would likely b +\- a few mph. So I suppose the argument being made by detractors of these apps. Are the flat out claims of top speed without acknowledging THAT discrepancy?
> 
> Or are people claiming that these apps. are unreliable and inconsitantly inaccurate enough that ANY given speed is questionable?
> Additionally, that still doesn't address my observation that similar apps used when I ride my MTB seem to B reasonably close to the milage & mph's logged with my bike mounted odometer! Again, usually anywhere within 3-5 mph. Any time I've encountered larger variences than that, they can usually b traced to signal loss or interference.
> ...


Average speeds will be accurate but top speeds can be off by a lot. If you look st a series of instantaneous speed indicators from GPS data it can be quite spiky.


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## redlude97 (Jan 9, 2008)

minute elevation changes on the mountain are very inaccurate. Simple geometry tells you that those inaccuracies get amplified when calculating speed. Hence, completely inaccurate readings even with the best GPS signal.


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## timmytard (Mar 19, 2009)

poutanen said:


> I tracked myself with apps for a couple years, various apps and various phones. My top speeds (after correction) were consistently anywhere from 100-130 kph each day.
> 
> Ah, shitty, I read that & was thinkin'....
> 
> ...


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## sabatoa (Jan 18, 2011)

Late follow up to this topic, but we did some testing to see how accurate these are. Check it out:









Speed Tracking App Accuracy


We tested the accuracy of ski and snowboard speed tracking apps. Read more to find out if your app is telling you the truth, or just trying to be nice...




www.agnarchy.com


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## BoardieK (Dec 21, 2015)

Good report, and "tough luck Chomps".


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## tanscrazydaisy (Mar 11, 2013)

Civilian GPS coarse acquisition (C/A) by design isn't too accurate. It's accurate enough

Military GPS is where accuracy matters. But civilian receivers cannot access Military GPS signals

Sent from my moto x4 using Tapatalk


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