Brian: I tend to change my tyres at just over 7000 miles, when they still have about 1000 miles left before the legal minimum I've used both PR4s and PR4GTs and in both cases, the tramlining didn't start until the last 1000 miles or so.
That's well weird David.
My experience was so long ago now I can't remember the mileage on the tyres at the time but I do remember commenting on it as soon as I got them fitted, which was just before the Italy trip. I imagine the big moaning write-up I did was after we got back, so about 3,000 miles in.
The white line tramlining wasn't too bad with the PR4's on my K12S. The worst was the 'tramlining' along broken longitudinal joints; the white line between lanes 2 & 3 on the eastbound M4 has broken longitudinal joints immediately to its right and that combination, in the wet, was lethal when filtering.
A few roads in Reading have a broken joint right on my 'natural' riding line and the bike simply refused to stay on line.