Do the speed limits only change on the gauge "after" the end of the train passes through the signal? I've just noticed distance fluctuations with how long the train is.
Yes speed limits will go up once the end of the train is past where it goes up e.g going from 20mph to 65mph you need to wait until the rear of the train has passed the speed sign. Speed limits that reduce from your current speed will come enforce from the front. e.g. going down from 65mph to 40mph
Thank you! I noticed that from the increase vs. decreased limits. I thought that's what was going on.
Think of speed signs/limits as being indicators of "zones". The speed limit which applies to the train is the lowest of whichever "zone" any part of the train is in. Long freight trains, or when going across points or in yards can sometimes span multiple "zones" - you could have a 50-car long freight train changing from one mainline track to another, so that the lead loco is in a 60mph zone and the caboose is also in a 60mph zone but because the middle of the train is going over a set of 15mph points, the limit applied to the whole train is 15mph
One notable exception to this rule is on the London Underground, where the speed limit applies as soon as the front of the train passes the speed board. I didn't realise it was a thing until DTG updated BKL to reflect this accurately.
The Tube can do that because all the trains are of a set length, so they know where to place the speedboards.
Except for north of Queens Park when the track is shared with Network Rail, the speed limit changes once the rear of the train passes the speed board.
I don't know if other trains have it but the Class 66 has a button in the cab, You press it when you pass a speed board indicating a higher speed and it beeps once the last wagon/carriage passes the speed board.
It's this one you want. Sometimes it'll beep a few seconds after the end of your train will pass but it will beep regardless of your train speed, Just press it when you pass a speed board for a higher speed limit.