I dont let em play with a tire either. As for the kong, i agree it might be better to let them chew it under supervision. But i know which are the destructive type of dogs and which just chew it. That has nothing to do with biting power.

I think it makes a little difference Macker. And if it doesn;t then it doesn't hurt the dog. I usually give the kong 5 days a week for the first 6 weeks (out of 8 ). Just 30 minutes.
I believe some regular chewing delays muscle cramp in the jaws and so keeps them able to maintain their natural biting power for a longer period of time. Just try and bite a stick yourself and see how fast your muscle cramp. Its because u never do it.
Its a nice activity for resting day as well when your dog is hyped up in a keep. I give em the kong at training time. Wont hurt the dogs bodyrest, but keeps him happy. Just trying to do what i can.