# Strava vs Bike Computer mileage



## OldManBiker (Nov 5, 2016)

**Note: If there is already an existing thread on this, please kindly direct me to the link and I'll go visit there and delete this. Thanks

I use Strava for my rides to track my mileage among other bells and whistles. But mainly to track the mileage that I set towards a Goal I set for myself at the beginning of each year.

I occasionally ride with some friends who have bike computers on their mountain bikes and our mileages never seem to match - EVER.

Am I being robbed of mileage by using Strava? I realize that Satellite/GPS has something to do with it as I ride but I am trying to justify my own reason to stop using Strava get go the Bike computer route.

Little help!


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## J.B. Weld (Aug 13, 2012)

Strava is just an app, what device are you using to collect the data? Phones and bike computers can both collect info from gps but bike computers have the option to connect a wheel sensor for more accuracy, maybe you can do the same with some phones but I don't know for sure. Also gps info is affected by how often your device checks it, the closer the intervals the better.

A properly calibrated wheel sensor should be near 100% accurate but where I'm at (sw US) gps is pretty accurate for mileage, good enough for me. 

So strava is only as accurate as the info it's given, at least that's the way I understand it. I'm no techie though.


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## adaycj (Sep 30, 2009)

A bike computer will never be accurate. The tires rolling radius changes as you load and unload it. It is more inaccurate over bumpy terrain. Even if the circumference perfectly matched in the garage or on the road it will be off when you are on the trail. It is also off when cornering, and when hopping or jumping. 

A GPS is terrible at determining altitude. And baro sensors to compensate don't work on quickly moving vehicles with varying air pressure. If you ride punchy trails with lots of ups and downs, it is the worst because it doesn't record hardly any of the ups and downs correctly. Crowd sourced data algorithms can help, as can topographical data when integrated with the GPS data. GPS tools also have a tendency to draw a straight line between two points, this is especially true if they loose signal for a number of data points. The straight section eliminates some of the curves and cheats you of mileage. 

I like Strava because it mostly uses the segments and its system to give me a way to compare myself to myself. But both the cycle computer and the GPS are wrong, and there is no easy way to fix them or make them match. Just pick the data you like best or you have the equipment for and use that for your goal. If you think Strava is robbing you, adjust your goal. It is the only thing you have full control over, and it is inherently accurate.


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## Harold (Dec 23, 2003)

adaycj said:


> A bike computer will never be accurate. The tires rolling radius changes as you load and unload it. It is more inaccurate over bumpy terrain. Even if the circumference perfectly matched in the garage or on the road it will be off when you are on the trail. It is also off when cornering, and when hopping or jumping.
> 
> A GPS is terrible at determining altitude. And baro sensors to compensate don't work on quickly moving vehicles with varying air pressure. If you ride punchy trails with lots of ups and downs, it is the worst because it doesn't record hardly any of the ups and downs correctly. Crowd sourced data algorithms can help, as can topographical data when integrated with the GPS data. GPS tools also have a tendency to draw a straight line between two points, this is especially true if they loose signal for a number of data points. The straight section eliminates some of the curves and cheats you of mileage.
> 
> I like Strava because it mostly uses the segments and its system to give me a way to compare myself to myself. But both the cycle computer and the GPS are wrong, and there is no easy way to fix them or make them match. Just pick the data you like best or you have the equipment for and use that for your goal. If you think Strava is robbing you, adjust your goal. It is the only thing you have full control over, and it is inherently accurate.


Yes and no.

And btw, this has been covered at some length here in the past, though it's been awhile. I don't think anyone has specifically started a new thread to ask the question for quite some time. And you probably know how terrible the search function on this website is.

I'd like to see the error introduced to a wheel sensor distance calculation due to the loading and unloading of the tire, or from riding technical terrain. Frankly, it's going to be more or less negligible. Anything with a wheel sensor will always be better than GPS-only calculated distance. How much better will depend on the trails. Straight-ish trails vs. extremely twisty trails is always going to be a larger factor than chunkiness. By a very large margin. And that is something you can address. GPS-only will be pretty good by itself on straight-ish trails. The improvements in distance calculations from a wheel sensor will be marginal. On twisty trails, it's something else entirely. A computer with a wheel sensor will be better by a large margin. This is because the nature of GPS calculated distance is that it's a connect-the-dots type of method. Your position is determined at some interval (which interval depends on the device you're using and the settings of that device). A straight line is drawn between each pair of sequential points. This shortcuts corners. An accurate GPS will ALWAYS measure a short distance around a curve. Increasing the recording frequency can reduce this error, but never entirely eliminate it. For bicycle GPS receivers, the highest recording frequency is about 1Hz, however, there's some relatively inexpensive GPS hardware out there that can record at 10Hz, giving much improved recording accuracy around curves. I think this stuff is most common for auto and motorcycle track use, because the higher speeds increase distance between recorded points.

Elevation/accumulated altitude is a whole other game. You only partly addressed that correctly. Yes, barometric altimeters have a recording frequency, also, and anything less than that doesn't get captured. That's no different than GPS derived elevation or crowd sourced elevation data. But the real problem with measuring elevation is more fundamental to the problem. No method exists to DIRECTLY measure it. Everything is an indirect method with a pile of assumptions behind it. These include the most basic assumption of the shape of the earth. The shape of our planet is only regular-ish. It's lumpy. It's uneven. Even the baseline (mean sea level) is not exactly the same everywhere, and the the sake of simplicity, we use a rough model (a mathematical model) to base our assumptions on. But OP wasn't even asking about elevation. Just distance.

So circling back to distance -

If you want the best mileage calculation, you can do what adaycj recommends and adjust your goals, or you can accept that while a wheel sensor is not perfect, it's better than GPS-only (especially if you ride very twisty trails), and use a computer with a wheel sensor to record your rides. Looking at your profile, it looks like you're not far from my neck of the woods (generally speaking, in the Southern Appalachians). Some trails are straighter (particularly older ones that follow old logging roads), but there are enough twistier trails that IMO, if you care about distance, a wheel sensor is worthwhile. My wife and I both use Garmin Edge 520s. It's funny, she didn't care about her distance so much, so I just got her the base computer. But I use a wheel sensor with mine (on both my mtb as well as my road bike) and she noticed that even though we'd do the same ride, my computer would record a couple miles more than hers. So she insisted on the wheel sensor. Now that we're both running essentially the same setup, our recorded distances are generally within a couple tenths of a mile and sometimes the same (at least to the level of accuracy that the bike computer calculates). That amount of error is generally acceptable to me. It's the sort of thing that can come up from imperfect calibration or variations in tire pressures used for different conditions, or whatever.

If I ride with someone who's using a phone, it's a serious mixed bag. Some phones have pretty good GPS hardware and they'll record pretty close. Others (sometimes very highly rated and desirable models) are absolute garbage when they're out of cell phone range (or cell connection is spotty or weak) and have to rely on the GPS chip only for position calculations (no augmentation from cell towers or fixed wifi networks or any of that business). IME, iphones are among some of the most terrible ones for their gps reception. You can look on Strava to see this with the Flyby tool. Overlay a bunch of people who were out at the same time and you can see who was using the app on their phones (and whether they were on an iphone or an Android - unfortunately, no better device distinction than that easily, anyway) or what standalone GPS model they used (at least if they uploaded a certain way - some models won't display since the upload is done via the manual upload tool which doesn't capture model information). It's pretty clear when looking at the map that phones are enormously variable from halfway decent to terrible and that standalone gps computers range from pretty good to okay. A good phone can be better than the worst standalone gps (usually it seems older models, but also some newer ones like the cheapest Garmins fall in here), but the extremes on either end don't really compare at all with each other.

It's worth noting that the wheel sensor won't do anything to change the positional accuracy of your track on a map. The wheel sensor essentially adds a couple additional data fields into the file your computer records. You'll still have the gps-calculated distance and speed numbers in the file, but you'll also have the same numbers calculated from the wheel sensor added to the mix.


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## coke (Jun 7, 2008)

I just track hours rather than miles. My Edge 520 seems to short me about 10-20% on most rides compared to people using wheel sensors.


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## Harold (Dec 23, 2003)

coke said:


> I just track hours rather than miles. My Edge 520 seems to short me about 10-20% on most rides compared to people using wheel sensors.


You do know you can pair a wheel sensor with your computer to get that straightened out, right?


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## Sidewalk (May 18, 2015)

I don't care about mileage*, just hours. 1000 miles are much easier on a road bike in Kansas than a mountain bike in the Alps.

*I had A LOT of miles last year.


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## BmanInTheD (Sep 19, 2014)

Long story short: GPS rips you off as much as 10-15% in tree-covered, twisty trails. A wheel sensor isn't perfect, but even with weighting and un-weighting, etc, will be within 1-2% of correct if calibrated properly. GPS sucks for distance for mountain biking (unless you are on wide-open, fairly straight trails); it's ok for road riding


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## chazpat (Sep 23, 2006)

OMB, GPS definitely cuts us short on the trails around here. I use Runkeeper and I used to log in on the website and adjust the mileage to be closer to adding up the listed trail mileage. The Avalanche trail always gets clipped a lot and comes out way shorter. I got tired of doing that and now just leave the mileage. I've run on some the Kennesaw Mt trails and been surprised at how accurate the GPS will be on them, just as I'm passing a sign with the mileage posted, Runkeeper will announce the same mileage. They are not so twisty so the GPS doesn't clip like on the mtb trails.

I used to use bike computers with wheel sensors and they would be pretty close to the posted mileage. If you want better accuracy, that's probably the way to go. Trick is to remember to clear distance on the computer when you start and then to record the distance at the end. Most will also record accumulative mileage. Also avoids when you forget to stop your GPS and it records miles driving home.


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## whtdel (Oct 24, 2008)

Harold covered pretty much the GPS aspect of the tracking technology, but as a rider from the North-East (relatively short ups and downs), my frustration comes from altitude accuracy of Strava/smartphones ... where an actual 100 feet of elevation will translate into a flat section (10 feet elevation) on Strava (at least where I ride).

To make a long story short, barometric altimeter are much more precise then GPS-based technology to evaluate altitude. So if we're using barometric equipped devices to track an activity, Strava will use the recorded reading from that device (allowing an acceptable precision levels as far as I'm concerned).

For devices not equipped with barometric altimeter (PLUS all those using their mobile app/smartphone), Strava uses their own database for specific areas to calculate the elevation, then smooth it out (to reduce noise).

In such, even if iPhone 6 and ups are equipped with a barometric altimeter, Strava does not make usage of actual (barometric) data, but prefer to rely on their much less accurate database! :madman:

Here's the most recent link : https://support.strava.com/hc/en-us/articles/115001294564-Elevation-on-Strava-FAQs


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## OwenM (Oct 17, 2012)

BmanInTheD said:


> Long story short: GPS rips you off as much as 10-15% in tree-covered, twisty trails.


That would describe my riding, and using apps on my phone it's 10-15% *minimum* when mountain biking, sometimes a lot more. I also showed a huge increase in elevation change on flat rail trail vs. mountain biking, which makes no sense. It would be within a mile or three of my bike computer on 50-75 mile rides that were a relatively straight line, though. 
I mtb a few laps of a 4.75 mile loop on a regular basis. Rarely breaks 4 miles on my phone, and sometimes barely 3. That's a huge difference. I'm fairly certain I've never hit 47mph on trails I average 8-10mph on, either, regardless of MapMyRide's claim
Have only bothered to try one other app, since I know it's the phone, and really just use it for time. Might as well use the stopwatch....
I'd really like to be able to accurately track my speed and mileage, and view the splits by mile, but assume that's $$$, if even possible.


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## J.B. Weld (Aug 13, 2012)

OwenM said:


> I'd really like to be able to accurately track my speed and mileage, and view the splits by mile, but assume that's $$$, if even possible.


I think wheel sensors are only about $50.


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## OwenM (Oct 17, 2012)

Yeah, I've got one on the hybrid I hardly ride, and have thought about swapping it over. I really like the thing where you can pull up the ride and view the individual miles on the phone, though. Problem is that it doesn't mean much when the speed and mileage are way off to begin with. It's about 100% tree cover here, which I'm sure doesn't help what's probably not a great GPS, anyway. It's not worth going to a lot of trouble over, just something to fool around with.


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## Harold (Dec 23, 2003)

OwenM said:


> That would describe my riding, and using apps on my phone it's 10-15% *minimum* when mountain biking, sometimes a lot more. I also showed a huge increase in elevation change on flat rail trail vs. mountain biking, which makes no sense. It would be within a mile or three of my bike computer on 50-75 mile rides that were a relatively straight line, though.
> I mtb a few laps of a 4.75 mile loop on a regular basis. Rarely breaks 4 miles on my phone, and sometimes barely 3. That's a huge difference. I'm fairly certain I've never hit 47mph on trails I average 8-10mph on, either, regardless of MapMyRide's claim
> Have only bothered to try one other app, since I know it's the phone, and really just use it for time. Might as well use the stopwatch....
> I'd really like to be able to accurately track my speed and mileage, and view the splits by mile, but assume that's $$$, if even possible.


Are you wanting to view splits by mile on the device, or later? There's a way to get that on a Garmin (probably would want to start at least with the Edge 5xx models for it, though) where you can set the device to "auto lap" at specified intervals, and then you can customize the data display to show lap splits. I don't know if competing devices can do that or not. The functionality doesn't really appear on the spec list for any of the Garmins and I only know about it because I use the lap split function (every 5mi, to cut down on the beeping), and I've seen the data field option in the settings for my Edge 520.

If you're okay with waiting to look at that information until you upload your data, lap splits are something that pretty much every data upload site will display for you. One thing they'll give you that I don't think you can display on the device, is to show you all of them together so you can compare (rather than the active one or the most recent one).



J.B. Weld said:


> I think wheel sensors are only about $50.


Looks to me like $40 should be a top end cost (REI's price on both the Garmin magnetless ANT+ sensor as well as Wahoo's RPM bluetooth sensor). Owen or anyone else could technically add a wheel sensor to their phone. Big question there is which sensors are compatible with which apps. Bluetooth sensors are more picky than ANT+ sensors, but the vast majority of phones do not have ANT+ wireless protocol. Most standalone GPS bike computers do, however. A standalone GPS bike computer would cost more outright, but it really is a better tool for the job.


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## eri (Sep 4, 2012)

OldManBiker said:


> Am I being robbed of mileage by using Strava? I realize that Satellite/GPS has something to do with it as I ride but I am trying to justify my own reason to stop using Strava get go the Bike computer route.
> 
> Little help!


Underreport isn't robbery! If it overreported it means youre robbed because you'll ride less.

Once I was doing the strava climbing challenge in a rainy winter month, I was doing hill repeats in busy traffic to get my vert in. One day I busted ass a full two hours, 1300m, but at the end I found i'd forgotten to start strava. I got no credit, the ride never happened, and I had to make up that vert in the next 4 days with an extra helping of fatigue.

Honestly I find my phone (iPhone 6s plus) is much more accurate than any of my friends garmins. If there is poor sat reception then the trace will be inaccurate. Maybe get a ble wheel speed sensor. But again, why do you care? I doubt it is making your goal unachievable.


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## scoobiemario (Aug 4, 2016)

So I understand the GPS clocking less miles than bike computer. It seems that Strava clocks 15% less than my bike computer usually. 
Unless I ride trails that are not very twisty. 

What is annoying, that both me and my buddy use strava when we ride together. We both have iPhone7, on Verizon. And pretty often our ride lengths are different!

Take it today: I rode extra half a mile to his house and back. But at the end his ride was reported 0.7 mile longer. 

Other example, last section of trail, we both left at the same time, and went fast. He arrived maybe 10 sec after me. Strava reported his time faster than mine. 

This is the type of inaccuracy that does not make much sense. If Strava could track all the rides within 5% of bike computer with wheel sensor, and was in general more accurate, it would be great. I like statistics, I like seeing that I improved, or not ;0) I just always have to take it with a grain of salt, and sometimes, with whole saltshaker!


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## adaycj (Sep 30, 2009)

scoobiemario said:


> So I understand the GPS clocking less miles than bike computer. It seems that Strava clocks 15% less than my bike computer usually.
> Unless I ride trails that are not very twisty.
> 
> What is annoying, that both me and my buddy use strava when we ride together. We both have iPhone7, on Verizon. And pretty often our ride lengths are different!
> ...


Yea, I did a 18.5 mile (about) ride with my wife this weekend. Her GPS/Strava device gave her about 18.2 miles. My GPS/Strava device gave me 17.2. Mine seems to be short on most rides, hers is closer to the published length. There is no way to adjust it on either device. The inaccuracies are not just from one technology to another, they are from one device to another too.


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## Harold (Dec 23, 2003)

scoobiemario said:


> So I understand the GPS clocking less miles than bike computer. It seems that Strava clocks 15% less than my bike computer usually.
> Unless I ride trails that are not very twisty.
> 
> What is annoying, that both me and my buddy use strava when we ride together. We both have iPhone7, on Verizon. And pretty often our ride lengths are different!
> ...





adaycj said:


> Yea, I did a 18.5 mile (about) ride with my wife this weekend. Her GPS/Strava device gave her about 18.2 miles. My GPS/Strava device gave me 17.2. Mine seems to be short on most rides, hers is closer to the published length. There is no way to adjust it on either device. The inaccuracies are not just from one technology to another, they are from one device to another too.


well calibrated wheel sensors will fix that, or at least will minimize it.


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## chazpat (Sep 23, 2006)

scoobiemario said:


> So I understand the GPS clocking less miles than bike computer. It seems that Strava clocks 15% less than my bike computer usually.
> Unless I ride trails that are not very twisty.
> 
> What is annoying, that both me and my buddy use strava when we ride together. We both have iPhone7, on Verizon. And pretty often our ride lengths are different!
> ...





adaycj said:


> Yea, I did a 18.5 mile (about) ride with my wife this weekend. Her GPS/Strava device gave her about 18.2 miles. My GPS/Strava device gave me 17.2. Mine seems to be short on most rides, hers is closer to the published length. There is no way to adjust it on either device. The inaccuracies are not just from one technology to another, they are from one device to another too.


I have an Android phone and I have a setting for "High Accuracy". It "uses GPS, WI-FI, Bluetooth, or mobile networks to determine location". So maybe your phones aren't set the same as who you are riding with. But yes, twisty trails get clipped a lot.


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## Harold (Dec 23, 2003)

Settings are always a good first place to look. But it is not uncommon for gps devices to vary significantly under slightly different conditions. Maybe they carry their phones in slightly different locations when they ride. That will result in different gps accuracy between them even with the same settings.


chazpat said:


> I have an Android phone and I have a setting for "High Accuracy". It "uses GPS, WI-FI, Bluetooth, or mobile networks to determine location". So maybe your phones aren't set the same as who you are riding with. But yes, twisty trails get clipped a lot.


Sent from my VS995 using Tapatalk


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