When you're standing in front of the machine, looking at the rear tires, the tread on the front face of the tire should look like:
V
V
V
If thay are almost bald, it probably doesn't matter too much, but they are "directional"--they get better traction turning one way than they do the opposite way. Obviously, since you want to push harder while trying to load the loader bucket, it's important that they be mounted the right way.
How about switching them, left side for right side? :wink2 (Think about it...)
I've had a spare rear wheel with an old tire laying around, and if I've needed it in a pinch, I haven't cared whether it was on the correct side or not.
A couple of years ago, I had a flat on one of my rear tires. I took it to a tire shop for repair, and when I got back to the machine, found they'd mounted it backwards. I took it back, and told them, and they apologized and said they'd remount it. I picked it up, took it back, and it was
still backwards. :Banghead The third trip, I stood there and watched them do it, the right way.