I just started using Strava about three weeks ago, and I enjoy it. But one of the things I've noticed is that the maximum speeds Strava gives are different than the speeds my cheap bike computer gives. On today's ride, Strava had me at a top speed (downhill) of 36.7 mph. My bike computer had me at 31.7 mph. Both times were on the same stretch of road. When I installed my computer, I hand measured the wheel circumference, and the distances given by the two aren't that far apart (Strava said I rode 28.6 mi. today and the computer said 28.5 -- no big deal). But the max speed thing baffles me. Any ideas?

Strava will often use changes in GPS position to calculate speed. Unfortunately, GPS position has a fairly large error so the speed can jump around a bit. Because the GPS 'noise' is random, the total distance will be accurate as the little errors average out to zero over the course of a ride.

Ahh. So would your advice be to accept the GPS distance measures, but not the speed measures?

I use a GPS along with an iphone Strava app. Over the past two years I've only noticed a few occasions of top speed discrepancies between the two. Typically the top speeds are within a few tenths of a an mph.

Trust the cheap bike computer. If properly calibrated (sounds like it is) it will give you far more accurate speed readings (especially compared to using the Strava app and the GPS in your phone).

Can't you equip your phone with a receiver for a magnetic sending unit for speed off the wheel? Wahoo or some such? Wouldn't that supply the accurate speeds to Strava all in one unit?

I don't think Strava top speeds are very accurate. On a recent ride it clocked me at 47.5 MPH. If that were accurate, I would have had to clean a load of poop out of my cycling britches.

My cycle computer is roll out calculated and dead accurate. My garmin GPS over and longer distance is as accurate . I find most of the time my cycle computer gives slightly higher max speed than garmin and garmin slightly higher than strava. The cycle computer probably has more up to the second data. Garmin requires you hold the top speed for a longer minimum time to count.