Originally Posted by
intransit1217
Any thoughts on speed sensor vs gps speed? If it reads by satellite, why do I need a sensor other than for cadence? Almost ready to go for a garmin 500 but trying to get the right bundle seems impossible.
GPS is subject to position errors (which are magnified when used to compute velocity or worse acceleration). Generally measured as VDOP and HDOP. More sophisticated Garmins (as used in aviation) have error measuring software (called RAIM) to predict performance. If bike GPS incorporated accelerometers that would probably obviate the need for a speed sensor, but without them the speed sensor improves the accuracy of instantaneous speed measurement/display. How important that is in the real world I can't say, though I can see that if GPS drop-out is a problem where you ride it could make a significant difference. I know if I ride through an underpass with "off course" alerting turned on, I will generate an off-course alarm. I can see it to be a bigger problem in urban environment where buildings will block line of sight to the birds.
To my way of thinking, what you bundle now isn't so important (you can always add a sensor later) but are you going to stick to ANT+ or use Bluetooth instead.
scott s.
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