GPS How Accurate?

[Rob Brookes]

Hi Folks

Having just got back into the sport I am now becoming more intrested in ride times and data so having signed up to Strava I would like to know what is more accurate a Garmin etrex 30 or a cateye wireless cycle computer?

 

[Rob3rt]

The cateye will account for the line taken around bends and weaving about, since it works on wheel rotation so speed and distance measurements are likely a bit more accurate, however it will not record your route and data in a very reviewable format.

 

[MrJamie]

I don't know the etrex, but a computer measuring the wheel rotations should be very very accurate if properly calibrated and consistent, gps slightly less so but still more than adequate for charting progress.

 

[Lee_M]

put it this way, if a gps was inaccurate none of the sat nav systems would work

 

[fossyant]

for strava you need GPS anyway !

 

[Rob3rt]

put it this way, if a gps was inaccurate none of the sat nav systems would work

GPS may be "accurate" arbitrarily assigning the term, but relatively speaking, the accuracy required for effective navigation is less so than for measuring distance travelled on a bike!

 

[Crackle]

My GPS and cateye, mostly agree. Where they don't, it's normally because of the way the GPS handles stops, or rather the software you use handles stops.

 

[Rob Brookes]

Now I have started using Strava and the GPS as a way of tracking rides and performance I guess this is how I should monitor progress and not jump between the two formats. Thanks for all the input, makes you think why didn't I think of that?

 

[Hacienda71]

Just wait until the next solar storm.

 

[Lee_M]

GPS may be "accurate" arbitrarily assigning the term, but relatively speaking, the accuracy required for effective navigation is less so than for measuring distance travelled on a bike!

agreed but the OP never said he wanted to measure distance travelled.

and if it was that inaccurate those cruise missiles would never find their mark.

I think GPS is acurate to about 15 feet at a single point, but over the distance of a bike ride that will be negligible. if it wasnt then accumulative errors would mean your sat nav would never work

 

[Lee_M]

agreed but the OP never said he wanted to measure distance travelled.

and if it was that inaccurate those cruise missiles would never find their mark.

I think GPS is acurate to about 15 feet at a single point, but over the distance of a bike ride that will be negligible. if it wasnt then accumulative errors would mean your sat nav would never work

actually I changed my mind, I dont agree, how can navigation work with an inaccurate distance measure?

 

[Rob3rt]

actually I changed my mind, I dont agree, how can navigation work with an inaccurate distance measure?

Re-read my comment, I did not state it was innacurate, I said the accuracy required for effective navigation is not necessarily the same as that for distance measurements accurate enough to account for things like your line through bends etc!

 

[Rob Brookes]

This morning I have been out and run the cycle computer and the GPS side by side to see what difference there is in the data. The GPS used is a Garmin etrex 30 with OS mapping installed and the cycle computer is a Cateye Velo wireless set up as per the instructions for the wheel size on the bike.

The ride I did was a little over 50 miles as per the GPS and can be found on strava here and returned the following data comparison:
Current speed generally seemed to be about 0.1 - 0.2 mph difference.
Ride Time - CC 3:07:47 GPS 3:08:07
Total Distance - CC 54.22 miles GPS 53.9 miles
Average Speed - CC 17.3 mph GPS 17.2 mph
Maximum Speed - CC 36.6 mph GPS 35.9 mph

Either way I think there is so little difference in the two that I am happy to chop in the Cycle Computer and just have the GPS taking up space on the bars> More so when the difference in the average speed is only 0.1mph and I have been using this as a measure for improvements in fitness.

Make of it what you will.

 

[Crackle]

The GPS I use isn't so good at instantaneous speed, seems to lag a little, though it all averages out OK. For that reason I still use a cycle computer as my main reference.

 

[Lee_M]

Re-read my comment, I did not state it was innacurate, I said the accuracy required for effective navigation is not necessarily the same as that for distance measurements accurate enough to account for things like your line through bends etc!

do people on here measure their rides that accurately?

seriously, what would be the actual difference? if you stay on your side of the road the differences would be minimal I would have thought