GPS Accuracy over Computer

dhayes73

I am sure that this has been talked about in here before, but just would like some thoughts on the accuracy of GPS over bicycle computers. Particularly in regards to "Current speed" and "Total Distance". Does a GPS just go from point to point when sync with satellite, while a properly set up computer will give actual ground covered, particularly on out rolling roads.

Any thoughts on this. My bicycle computer died recently and looking for advice on standard computer or GPS.

Cheers in advance for advice.

Inquitus

A computer is better for "Current Speed", as that's a real time measurement whereas gps can be impacted by tree coverage etc. That said both will give the same results over the course of a ride for "Total Distance" and "Average Speed"

Leroy42

IMO there is always a difference, the actual wheel sensors giving a better result than the GPS. It also avoids any drop out due to loss of signal (Bridge, tree coverings etc).

However, the difference is negligable, it certainly won't make any real difference. While comparing a sensor based with GPS would probably give some differences, once the total distance and total time are relatively close than not much of a problem.

Does it really matter if the ride registers 100.6k or 101.6K with the change in avg speed?

dhayes73

Leroy42 wrote: »

IMO there is always a difference, the actual wheel sensors giving a better result than the GPS. It also avoids any drop out due to loss of signal (Bridge, tree coverings etc).

However, the difference is negligable, it certainly won't make any real difference. While comparing a sensor based with GPS would probably give some differences, once the total distance and total time are relatively close than not much of a problem.

Does it really matter if the ride registers 100.6k or 101.6K with the change in avg speed?

All relevant, and fair enough. I am not fussy if its out by a bit, as just a part time sportive cyclist, not a TDF potential. :-). The handiness of a GPS, and being able to upload to PC would suit me. I actually had not thought of the loss of signal due to overhead trees etc, etc. I was more thinking of the lack of accuracy due to GPS measuring point to point, where bike computer measures the ground covered.
Anyway, I am babbling again, cheers for the feedback.

Inquitus

dhayes73 wrote: »

All relevant, and fair enough. I am not fussy if its out by a bit, as just a part time sportive cyclist, not a TDF potential. :-). The handiness of a GPS, and being able to upload to PC would suit me. I actually had not thought of the loss of signal due to overhead trees etc, etc. I was more thinking of the lack of accuracy due to GPS measuring point to point, where bike computer measures the ground covered.
Anyway, I am babbling again, cheers for the feedback.

The gps polls your position every second, so while technically it is point to point, the points are soo close together as to not matter.

dhayes73

Inquitus wrote: »

The gps polls your position every second, so while technically it is point to point, the points are soo close together as to not matter.

Ah, great stuff. Suppose thats what I was looking for. :-). Thanks

smacl

Wheel typically gives better results over shorter distances, and is giving you slope distance. GPS will be more accurate over longer distances and typically reports plan or 2d distance, so will typically be a small bit shorter. Both suffer from different types of error. Wheel can have a small systematic error if the radius used is slightly out due to tyre size for example, and may be less accurate on rougher surfaces. GPS can have gaps due to lost coverage, and the occasional big error due to effects such as multi-path and constellation geometry.

As Leroy42, the differences are seldom enough to concern a cyclist. More pragmatically, a GPS is more likely to run out of battery first, whereas a cheapo cateye is very reliable.

quozl

If I recall correctly my Garmin 510 calibrates wheel diameter using the GPS and then uses the wheel magnet to give speed values.

So it would be the same as a normal bike computer plus the wheel diameter should be very accurately calibrated without having to do a roll-out test.

Roadtoad

Battery life, more likely and easier to have a full season's info on the simpler gadget. If you keep a good diary.
Better info e.g. altitude, favourite route comparisons on the bigger machine.