Originally Posted by CliffordK

I like to unroll a tape, and measure the actual roll-out of my wheel to calibrate the cycle computer.

In your case, 4.76 and 4.8 miles are likely identical with respect to the accuracy of the devices. A longer ride would be a bit more telling. So, any differences in average speed would be due to different calculations of time. So, time elapsed between the point where Strava was turned on or turned off, or any stops during the ride.

One thing you might try is to crop your ride on Strava... Just skim a couple of yards of riding off of each end of the ride.

On the Analysis page in Strava, you can also choose to display by time rather than display by distance, and any pauses should show up.