Mark J. wrote:
On 2/10/2021 9:40 AM, Mark cleary wrote:
I have a Garmin 910xt that I use for the bike of course GPS keeps track
of my speed. I decided to get the rear speed sensor that goes around the
rear hub and should come today. So I realize that indoors it makes sense
but what about using it outdoors with the GPS. My understanding is the
speed sensor will overrule the GPS speed data. My years of using this it
is pretty much dead accurate for distance so speed should be deadly
accurate. I have done many long rides and hit the same mileage marks
almost within 10-50 feet for 20-40 miles.

I also bought the cadence sensor and have never used a cadence sensor
figuring I can count my cadence anytime I want. So do any of the group
use a speed sensor when riding outdoors? I guess you can hook it up with
Zwift but I have never used Zwift don't see the benefit as long as I
know my speed on and heart rate on the trainer. I have a cateye at the
moment set up for the back wheel on my trainer bike. I give this garmin
a go. Some how Zwift measures power but I cannot figure out how that
could be anything more than an educated guess.
Deacon Mark............in the very cold midwest


Yes, I've used a speed sensor / wheel sensor on two bikes for my Garmin
Edge (handlebar mount GPS).

I'm pretty sure you're correct that the wheel/speed sensor overrides the
GPS signal for speed and distance... sort of. There's some subtlety,
though. The Edge calibrates wheel size automatically - it never asked
me to input a setting - I think by comparing with the GPS. Then I
expect the sensor is used to overrule the GPS when the GPS "glitches."


I use speed and cadence sensors with my 830. I find it more stable for the
speed sensor than GPS
The speed sensor takes precedence but it’s a bit glitchy. For example if
you’re on a ferry and the gps picks up motion it may override the speed
sensor.

If you have a "dumb" trainer, yes, Zwift estimates power based on speed
- and is notoriously crude about it. Common wisdom on Zwift discussion
groups is that one usually sees a major power "loss" when switching to a
wheel-off smart trainer. I.e. that for wheel-on or dumb trainers, Zwift
overestimates.


I don’t use Zwift but in general I agree. Switching from a vortex to a
flux 2 caused a major power loss. The simulated incline went from 6 to 16%
as well.


Mark J.