Hey @Activestepup, 
Your max speed for an activity on Strava is calculated from the GPS coordinates in your activity. We don't perform any smoothing or averaging between speed readings, so max speed is simply calculated from the maximum speed between two GPS coordinates. If GPS inaccuracies occur with some of your data (which, to a certain extent, is always the case), max speed can be inflated accordingly. The good news is that these high speeds generally occur for the span of only one GPS point, so they don't really have an effect on your activity's average speed.

If you're not able to see the Performance graph ever reach the speed quoted as your activity's maximum, the problem is most likely that the view you're seeing is too far "zoomed out". Because that questionable max speed occurred for such a short period of time, you may have to click and drag to select a portion of the Performance graph and zoom in on an area with poor GPS data. This will most likely give you the ability to see where and when in your activity the maximum speed recording took place.

For more information, see our article on: problems with GPS data.