Ok, let's ask ls4me what his pressures were when the centers wore down. Contrary to what you would believe, it can actually be caused by underinflation in this type of tire. If you've ever seen top fuel dragsters burn out or take off, their rear tires get narrower and stand tall, increasing the circumference in the middle of the tires, due to flexing and centrifugal force. The more air pressure that we keep in our tires, as in ultra high performance radials, the more pressure that the sidewalls have to pull the contact patch from the outsides and making it more flat. If we run too little air in the tires, they have a tendency to ride on the middle of the tire tread patch, the faster we get them spinning. I typically ride around at 75-80 and have seen this happen on both of my cars. If they run at factory recommended pressures, like 32 or around that, the wear is noticeable and rapid, even with a 400 treadwear rated tire. Running up around 38 seems to make them last longer. The rear tires wear out their centers due to the rear wheel drive continually pushing the car forward off those treads. If the center is bowed out with a centrifugally enlarged center track, the all of that long term driving force for the car is concentrated on that middle patch of tire. The front tires do not suffer from this as much, since there is no propulsion to those tires.
There used to be an article written by BF Goodrich engineers at the link inside this post I will point to, but it's a little old and gone now. The poster summarized it and it is contained in this link.
http://www.mercurymarauder.net/forums/showpost.php?p=67456&postcount=7
