Not a good idea.
Even though this would not be good, a FWD vehicle pulling two different sized tires in the rear, I could see that the car would not really care what was back there as they would just be free-wheeling.
In your question, one tire is a different size and your vehicle is AWD, meaning it drives from the front and the rear.
It has two differentials, which mainly compensate for turning. Whereas one wheel travels further than the other during the turn. The differential allows the turn to work smoothly (instead of dragging the wheel traveling the further-est or it 'hopping' around.)
What would really be happening in your scenario is the vehicle would constantly 'think' that that axle was in a constant turn, like never ending! One wheel travels further (or lesser) than the other on one axle rotation
Maybe the differential might compensate for that axle, But now that axle ratio is different from the other axle. The axles cannot have different ratios, as they would fight each other constantly and bind against each other.
Now lets throw in a computer and computerized drive train. Surely, it too, would get confused and try to compensate for the glitching.
I would say for sure that mechanical things might suffer, and maybe your safety too.
Sorry, I would give the idea a Thumbs Down!
Sunday, November 27th, 2016 AT 6:16 PM