Weight Weenies

righty I recently got a garmin edge 800 with cadence and heartrate for a cheap price. Im planning on selling the cadence thing, however having just looked at it, its actually called a 'wireless speed and cadence sensor'. Up till now Ive just used the units gps to determine my speed - my question is whether if I installed the cadence/speed sensor, does this give a more accurate measurement of speed or is it not really necessary if Im not interested in cadence?

merci!

It's only useful for indoor training....

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Disagree.

The speed and cadence sensor avoids dropouts in speed when you ride through trees, underpasses and other places where GPS doesn't work. The GPS and speed sensor work together so that the speed is calibrated automatically. Without the GSC10 my forest rides were frustrating.

really depends if speed matters to you.

Mr. Fish is right, the GSC10 is the way to go. You can manually calibrate your wheel cirumference for a very accurate reading. My girlfriend rides without the sensor and when we're riding together her garmin sounds like it's getting mad at her with it's beeping whenever it loses it's signal, particularly in forested areas with a lot of tree canopy overhead. And it does it a lot, whereas mine with the speed/cadence sensor never does that. We'll be putting one on her bike soon and she probably doesn't really care, but she's not as picky as me.

As others said its absolutely more accurate with the speed cadence sensor.

...or

1) It is extra weight and, most of the time, unnecessary.
2) It negates the beauty of a GPS-based computer: you can easily move that one unit between bikes in a matter of seconds without having to move extra sensors nor buy additional sensors for each bike you own.

Either way, your choice.

+1
This is weight weenies after all..
I have a gc10, in a box some where...

yup, sold it!

That's great that there're people who sell them on, so those who value it can buy it.
If you have a power meter and thus a cadence reading from the power meter I'd say the GSC is not neccessary on a road bike.

I have an 800 and a powertap G3 but do not use the speed/cadence sensor. I have no issues with this configuration EXCEPT when I do indoor trainer rides and upload to Strava there is no data to be had.

I've always found it hard to get the GSC10 to reliably record speed (even when you manually set the circumference of the wheel) - so I just stick with GPS and record the cadence. I've had rides skewed by up to 30% by the speed sensor not reading correctly. For me they're too finicky and I'm more relaxed about the cadence being 100% accurate.

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For anyone unaware. If you set the speed to auto on the Garmin 800 it will use GPS data in comparison with what it is seeing as a speed reading from the wheel with the GSC-10 and set tire circumference based on that. If you have a GSC-10 it will use it because it is more accurate then GPS data.