Has anyone heard of a donut tire damaging the transmission or differential because of the size difference? I heard that it could happen, but never heard that it has happened.

I am sure many people have used the donut for thousands of miles on the front axle of a front wheel drive car because they just don't have the money to buy a new tire. I have actually seen cars with the donut tire on it for months in the neighborhood.

If it could damage the car over long distances, why wouldn't it damage it during short distances or what if you use it for 5 - 10 times at 20 - 40 miles each time - 100 to 500 miles total over six or seven years. Why would they allow a donut tire if it would damage the car? During these days with so much road construction, multiple flats per year and more than 50 miles of one day's commute before getting the flat tire repaired is not uncommon.