# More accurate, GPS or bike computer?



## JBH (Apr 11, 2008)

This seems to be always up for debate when discussing with others. Any thoughts from the masses? Thanks!


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## Buster1971 (May 11, 2009)

Unless moving in a straight line a properly set up bike computer that measures distance the wheel travels is more accurate. This is because the GPS is measuring the distance between points the GPS marks at specified times. If these points are a second a part the measurement will be a straight line between which on a turn is not the true distance the wheels have traveled.


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## ghettocruiser (Jun 21, 2008)

A device with a wheel sensor is the most accurate, provided it has the correct wheel size input.

GPS units with wheel sensors allow you to calibrate exact wheel size easily if you change tires, or even substantially change tire pressure.

So that's my vote... the combo.


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## G8TR (May 10, 2012)

What about when the wheel is off the ground spinning or the brakes are locked, but the bike is still moving? Some gps's allow you to adjust the time between satellite pings so you can get a more accurate reading on trails with switchbacks and curves, but it drains the battery faster.


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## Harold (Dec 23, 2003)

G8TR said:


> What about when the wheel is off the ground spinning or the brakes are locked, but the bike is still moving? Some gps's allow you to adjust the time between satellite pings so you can get a more accurate reading on trails with switchbacks and curves, but it drains the battery faster.


no.

more frequent recording does not drain the battery faster. the GPS does not "ping" the satellite. it sends nothing unless you're talking about a phone using a data connection to download maps or use AGPS to speed signal acquisition. the GPS is a receiver only. it receives the signal from the satellites and does calculations onboard. more frequent recording fills the memory faster, but receivers nowadays have enough memory available that this isn't a problem.

My Oregon 450 has 850MB of memory, and in spite of its 10,000 point tracklog "limit" (for the active log and for each saved track), it has the ability to auto-archive segments in 2000 point sections. I can run 1 sec recording for as long as the battery holds out (18+hrs) and still have memory left over.

getting air with a wheel sensor can add to inaccuracy, but I'd hedge my bets that it's marginal, at most. Maybe not even measurable with the 0.1mi precision on most computers. You'd have to be getting a LOT of air over the course of a ride to measure a 0.1mi discrepancy between a bike that had an equally well calibrated computer with a wheel sensor that got zero air on the same lines.

as for locking the brakes, I cannot recall the last time my wheels were locked for any appreciable amount of time while riding. when that happens, ESPECIALLY to the front (where most wheel sensor magnets are located), you'll be crashing soon.


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## ghettocruiser (Jun 21, 2008)

Haha. Maybe if you had a sensor on the front wheel, and did a lot of looooong wheelies.

I've ridden with guys who might actually have that problem, although none of them had had much use for speedometers.

_I also had an idea for a little servo that could pull the GPS wheel-sensor arm in to give a temporary zero reading at stop signs, even when the bike didn't come to a full and complete stop. You know, in case anyone checks up on your Strava logs. _


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## JBH (Apr 11, 2008)

Thanks for the input. I figured the gps to be off a bit due to switchbacks etc. It seems like most of the rides in the 15 mile range will put about a mile difference between the bike computer and the gps on my local trail system.


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## Scale20tgn (Jun 27, 2012)

Hello,

I've compared GPS and bike's computer, and I think that GPS is more accurate that my bike computer, maybe my bike computer is not prefect installed.

Thanks!!!


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## JoePAz (May 7, 2012)

JBH said:


> This seems to be always up for debate when discussing with others. Any thoughts from the masses? Thanks!


Bike computer... 
My GPS is based on a phone and samples. On twisty single track it can miss some spots and cut corners. This pretty clear if you overlay the GPS log over a satalite view of terrain. Useally you can see the actual trail and where the GPS track takes short cuts. My rides are always shorter on GPS thay wheel based bike computer. If course if you enter the wrong wheel size you have an error too.


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## DennisF (Nov 4, 2011)

The main thing for me in favor of the computer is convenience and reliablility. I used my cell phone GPS for a while, but got a computer. The GPS app had to be turned on and off, started losing satelite lock more often as spring came on and the tree canopy grew, had to wait for GPS to lock when you turned it on (I don't have a data plan for AGPS), was more difficult to mount, and battery life was an issue.

The computer is as easy to use as the speedo/odo on your car.


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