speed camera

[Grahamm]

There are average speed camera on the M27 at the moment, signed as set to 50mph. When I keep a steady 50 through them I seem to be the slowest thing out there and yes, tailgating happens a lot. (Why?)

If possible, I use alternative routes which avoid that section because it is intensely tedious, but still requires a lot of concentration to keep below the limit

But if I ride at 50mph according to my speedo, my sat nav says I'm actually doing about 45mph.

If I ride at an indicated 55mph, the sat nav says I'm doing 50.