Originally Posted by Hiro11

I personally don't see the need for speed sensors with a GPS head unit. The average speed results I get off of GPS are very consistent with those from people I ride with who have speed sensors. I get that there's a lag while accelerating / decelerating but this appears to work itself out over time. Instantaneous speed doesn't seem very important to me, especially given that I have instantaneous power and instantaneous heart displayed on my head unit, both of which are better measures of effort. Regardless, the speed updates in a second or so.