I have 235/45/17 all around and now have a spare 225/55/16 on the rear, circumferences are 79.54in for the 235, and 80.86 for the 225. Is this enough of a difference to damage the diff? I have already went around 40mi, and will not have the replacement tire for a few days. The tires are basically new so replacing one should not be a problem, just need to know if I should stop driving now. When i first put the spare on, there was a sound like grinding brakes under 20mph coming from the rear, but it magically went away by itself, hopefully that wasn't the diff already being destroyed.

 

i would drive as little as possible... even slight differences in size, like a snow tire and summer tire are supposed to be horrible for the AWD system

 

Does anyone have more input on this issue? I have my fullsize spare on and the tires new vs the other ones having maybe 1/4 less tread.