P121>>You must not drive a type of vehicle that is restricted to a maximum vehicle speed limit of 80km/h or less in the traffic lane nearest the centre median of the motorway (the outside lane). An exception to this
prohibition applies at any location where the speed limit is 80km/h or
less.
Is it just me that’s confused or am i missing something obvious?
Unless the maximum (alleged 
) limited speed for Irish artics is 80kph instead of the usual 90, then the above rule would not apply.
Driveroneuk:
P121>>You must not drive a type of vehicle that is restricted to a maximum vehicle speed limit of 80km/h or less in the traffic lane nearest the centre median of the motorway (the outside lane). An exception to this
prohibition applies at any location where the speed limit is 80km/h or
less.Is it just me that’s confused or am i missing something obvious?
Unless the maximum (alleged
I think your missing something! You have speed limited for roads (e.g. UK Motorway 70mph) Then you have a speed limit for types of vehicle (e.g. UK Motorway HGVs 60mph, but varies according to class of road).
In Ireland you have speed limits for roads (e.g. IRL Motorway 120km/h in places) and speed limits for types of vehicles (e.g. IRL Motorway HGVs 80km/h) Now the difference is that this doesn’t vary according to the class of the road.
So on a motorway, the if the (type of) vehicle speed limit is below that which is sign posted, then the lower limit applies. If the vehicle speed limit is the same or higher, then the sign posted limit applies.
Therefore on a single carriageway road, if it says 80km/h, the you can go 50mph in your lorry.
The outside lane rule works according to the above. If the section has a sub 80km/h limit you can use the outside lane. If it doesn’t then you can’t.
Now back to the real world… 
The two Irish trucks I have driven had speed limiters calibrated to 85km/h. I can only get 90km/h showing on the clock when I hit the limiter. Have a look at the tachograph section and you can see my first two speed traces.
Still a bit odd the the limiters are 85km/h when the limit 80km/h, just like it isn’t the same for UK 90km/h for a 60mph limit. Bonkers! 
To be honest I really don’t consider the speed limit when driving here. I just drive according to conditions. Sometimes slower, often higher. Not like in the UK when you spend so much time worrying about scameras that’s a complete distraction from more important things.