A friend of mine had an accident with a FWD car that had almost bald tires at the rear. Na total damage yung car cause it wasn't a head on collision but a side collision... no "crash structure" there... good thing the impact was on the passenger side... my friend survived with a few broken bones and some titanium plates on his skull ;)
This is what happens if you put bald tires at the rear and drive at highway speeds: (happened just 3 months ago)
This is a picture from the local paper. Immovable lampost meets AE92 corolla.
This was taken at the shop after they had it towed.
MORAL: Don't drive with bald tires... mura lang naman yung mga surplus tires ngayon, Php 700 per tire lang. Compared sa mga hospital bills that you are going to get if you meet an accident, not to mention your life on the line
around seven years ago, my rear right tire blew up while i was running around 80 kph going to calamba (SLEX from Alabang).
when it exploded, my car went on a 720 degree spin and controlling the car was really impossible. it was just luck when i landed on the center area of the SLEX then.
i would go for niky's opinion. it is much safer if you put the bald ones at the front. at least, steering will still be possible.