A problem with this trick is that there’s often a large rebate only when you buy four tires, so you may not really be saving much. For example, when I last bought tires they were ~$130 each Michelins but there was a $100 rebate for buying four.
Actually, to be more specific, I also had 2 that got damaged and pro-ration came out to paying about 80%. I negotiated up 0.5-1cm on the pro-ration credits (worth ~$30x2) as I said I otherwise definitely would ONLY replace the two that were damaged, but if those prorated a little better then I would replace all 4. So, I replaced all four tires. After the $100 rebate I only ended up paying for about 1 1/2 of those 4 tires (plus the ~$30/tire install/tpms fees, though, or whatever Discount charged at that time).
A second problem with using the spare is that most vehicles now don’t have a full-sized spare. (I have a spare full-size tire in my house due to this issue)
And, finally, a third problem (depending on how many miles you drive) is that the “spare” may end up being too old. If you replace tires every 4 years and you use a 4yr old spare – It would be 8 years old which seems pretty bad on the rubber, especially depending on climate where you are and depending whether you store it in a climate controlled area or not.
(I know, the quote is from the older thread 4 months ago… but since they’re merged…)