Big tyre pressures

[b'have]

Anyone know what pressures to run in 305 25 20 rears? These are very non standard, so recommended pressures don't mean anything.

[Alex]

I'd start with 30psi and see how they wear...you can't really tell till you see wear in them...

[JohnA]

Charlie have you got a non-contact thermometer?
They have come down in price a lot lately, and they are invaluable in calculating the ideal pressures for the friction/weight/atmospheric conditions you've got.

You start from a fixed pressure and then change up or down aiming for a uniform operating temperature at the tread area.
It takes some time but when you get it spot-on it's worth it.