Four rear wheels...?

[RichardJW~]

yes, usually when you took the wheel off and only after discovered the bu99er was full of water

[Dah]

I imagine it's surprising how much weight the water adds. Half ton maybe?

[hair bear]

77?

Sorry Richard, didn't have that one long and can't remember what year it was, more likely early 80's.
Only ever used water ballast in a 35x at 90% full for match ploughing. You don't want to try road work at 50% full, if you stop quick at a junction it wants to lurch back and forth - most unprofessional.