I have 5k mile old 33" BFG K02 All terrain tires on my 97 80 series. I have not rotated them yet. I noticed that the back two tires had a lot less tread than the front. Also significantly less tread than the brand new spare. I thought this was odd as they only have 5k miles. Also why just the two back ones? I figured if any it would be the front. Can anyone chime in on this? What's the issue or is this common? I run them at 35 PSI cold and they go to around 42 when hot.
Pic of the rear
Pic of the front
See the big difference?
Pic of the rear

Pic of the front

See the big difference?