Speed sensor, swapping wheel size.

[delthebike]

Will a Garmin Speed Sensor accurately report speed if it is removed from a 700c wheel to a 406c wheel? 
eg, move from road touring bike to Brompton.

[LittleWheelsandBig]

Pedant: Brompton is 349. Many Dahon-alikes are 406.

[lissotriton]

The speed sensor just counts revolutions.
Wheel size depends on what GPS device it is connected to. Think most Garmins will autocalibrate for wheel size, based on GPS. But not sure how often that happens - will it be recording inaccurate data for a while, before it figures out the wheel has changed?
Or some models let you manually specify the wheel size.

[BFC]

Will a Garmin Speed Sensor accurately report speed if it is removed from a 700c wheel to a 406c wheel? 
eg, move from road touring bike to Brompton.

When switching the sensor between bikes will probably need to "remove" then "add" the sensor (in the Garmin menus) to force a recalibration of wheelsize. Try to ride "normally" until the recalibration has been completed (do not weave to check the stearing/headset, try and avoid junctions etc). If you have more than one speed sensor go through the pain of naming it on the device so you know which one to remove next time.
I guess it's something you won't be doing too often, they are a pain to physically remove and fit!
If you have a decent voltmeter check the battery whilst the sensor is off the bike/wheel, saves taking it off again after a few hours use.

[delthebike]

When switching the sensor between bikes will probably need to "remove" then "add" the sensor (in the Garmin menus) to force a recalibration of wheelsize. Try to ride "normally" until the recalibration has been completed (do not weave to check the stearing/headset, try and avoid junctions etc). If you have more than one speed sensor go through the pain of naming it on the device so you know which one to remove next time.
I guess it's something you won't be doing too often, they are a pain to physically remove and fit!

That makes sense, remove and add sensor. 
I doubt I would do it at all, just curious.
Thanks all!