Is there an article that explains the PokeStop speed limit and "Please Try Again", both manually and with PoGo Plus?

Please try again , is also related to server and loading ie ( you spin a pokestop while the game loading and or the stop is already used but signal didn't come from server and didn't reflect on it )

I can consistently spin stops at 20MPH or less. Anything over that usually not.

Also, if I recently acknowledged the "You are going too fast" it doesn't matter unless I slow down to under 5 MPH.
And, what the person above me said! ^^^

There's a stretch that runs through our downtown and if I have the watch going or go plus 25mph is very clearly the cut off for me. That won't consistently log km, but I can spin every stop at 24 mph.

I try and take glances at the nearby poke list. If they're visible you should be able to spin, and as soon as you break 25mph, they disappear and stops will start telling you to try again

25 is the limit i have found