If the Garmin speed sensor and GPS (FR 935) are on, what is the priority in the speed readings?
Triathlon Forum
Login required to started new threads
Login required to post replies
If the Garmin speed sensor and GPS (FR 935) are on, what is the priority in the speed readings?
Re: Priority Speed Sensor or GPS [ttsnail]
[ In reply to ]
If the GPS is on (GPS or GPS+GLONASS IIRC) it will use both. When using both, you can’t really see what’s going on as it’s likely all being fed into a predictive filter Inside the GPS. GPS off is the only way to ensure it only uses the speed and distance sensor.
In terms of accuracy:
Speed sensor only- best (with correct rollout set)
Combined - better and may be over a long run better as it sets the rollout for you.
GPS only- worst
When doing aero testing for example, turn the GPS off because you want accurate instantaneous speed values.
Developing aero, fit and other fun stuff at Red is Faster
In terms of accuracy:
Speed sensor only- best (with correct rollout set)
Combined - better and may be over a long run better as it sets the rollout for you.
GPS only- worst
When doing aero testing for example, turn the GPS off because you want accurate instantaneous speed values.
Developing aero, fit and other fun stuff at Red is Faster
Re: Priority Speed Sensor or GPS [SkippyKitten]
[ In reply to ]
SkippyKitten wrote:
If the GPS is on (GPS or GPS+GLONASS IIRC) it will use both. When using both, you can’t really see what’s going on as it’s likely all being fed into a predictive filter Inside the GPS. GPS off is the only way to ensure it only uses the speed and distance sensor. In terms of accuracy:
Speed sensor only- best (with correct rollout set)
Combined - better and may be over a long run better as it sets the rollout for you.
GPS only- worst
When doing aero testing for example, turn the GPS off because you want accurate instantaneous speed values.
On a long course with relatively few corners and in an open area where buildings, tunnels or dense forest aren't going to interfere with GPS accuracy, I'd expect GPS to be better than the speed sensor. The speed sensor is best for instantaneous speed indication but the GPS should be good for distance and average speed.
As far as I remember Garmin devices used to default to GPS for distance providing it had a signal and only used the speed sensor for indicated speed. When it didn't have a GPS signal it would revert to the speed sensor for distance. I haven't paid attention in the last few years so I don't know if that has changed on more recent devices.
Re: Priority Speed Sensor or GPS [Ai_1]
[ In reply to ]
Running 2 or more GPS and odometers on my bikes most of the time may have given me a little insight. :)
One thing that i didn’t mention above is that (In the U.K. at least, 50°+ North) GPS+GLONASS (+ WAAS) is a lot lot better than GPS alone.
Developing aero, fit and other fun stuff at Red is Faster
One thing that i didn’t mention above is that (In the U.K. at least, 50°+ North) GPS+GLONASS (+ WAAS) is a lot lot better than GPS alone.
Developing aero, fit and other fun stuff at Red is Faster
SkippyKitten wrote:
If the GPS is on (GPS or GPS+GLONASS IIRC) it will use both. When using both, you can’t really see what’s going on as it’s likely all being fed into a predictive filter Inside the GPS. GPS off is the only way to ensure it only uses the speed and distance sensor. In terms of accuracy:
Speed sensor only- best (with correct rollout set)
Combined - better and may be over a long run better as it sets the rollout for you.
GPS only- worst
When doing aero testing for example, turn the GPS off because you want accurate instantaneous speed values.
I'm pretty sure it only uses the speed sensor for speed if you have that connected. A quick test I've done sometimes is to lift the wheel and spin it. It then shows speed on the display that seems to match the wheel speed pretty well even though the bike itself is stationary. I don't know whether this will depend on whether you have wheel roll-out set to automatic or manual (I have mine set to manual). Neither have I checked whether the distance will stay at zero or it will use the distance calculated from the speed from the wheel sensor.
For the last couple of years I've used Garmin Edge 1000 when testing, so other devices may behave differently - and it may even depend on firmware version.