cyan328 
Taller tires should be on the back to avoid TOD fluctuation but if you have noise or grinding then something more severe has happened. Good thing you did not have a flat on the rear as you would have had to move the front tire to the rear and put the spare on the front - according the manual AND printed on the spare.
BTW, if you haven't checked the air in the spare, you ought to at least every other month. And you have to remove it to check it easily but I could see bigger problems if you tried to use it and it was shorter than it is.
