i was told by lexus nottingham that it was a 'characteristic' of the car just like the high fuel consumption!!
i did insisit that they should contact WIM and get the settings from there as it was a known issue on the owners club.
if its any help i have the print out where they advised that the new revised settings were applied, not really knowing which they used i just took there word that it would solve the problem...
to be fair though, my geo was done there as it was paid for from the company that i bought the car off and it seems to be ok.. 10,000 miles and no strange tyre wear! dont know if its got anything to do with the weight in the boot??