New tires

Must you always buy 4 new tires when you have a blowout, or nail in the sidewall?

Also…how often should you rotate tires?

ONLY on AWD MUST replace all 4 tires.

Open your drivers manual. In general every 5-7k miles.

It would be a lot more helpful if we knew what vehicle this was for.

I believe it is a subaru outback (tag line) in which case it is probably AWD in which case, yes - all 4 tires should be done. This info will also be specified in the owner’s manual.

Yes, your Subaru probably needs 4 new tires. Unless the other three are virtually new, with no visible wear, you need 4 tires.

The AWD system in your Outback is very sensitive to difference in tire circumference, and can be damaged by mis-matched tires.

The owner’s manual will tell you how often, and in what manner, to rotate the tires to keep them evenly matched and prevent AWD damage.

Most or all Subarus require matching tires to avoid damage. Your owner’s manual should spell this out clearly.

Another option is buying one tire and having it shaved to match the other three. Not that many tire shops can do this, so call around or order from Tire Rack online.

The rule on Subaru AWD is if the difference in circumference between new and old tires is more than 1/4" replacement of remaining four is needed. My 25 year experienced Subaru master tech/independent says 1/2" is fine in his experience. 1" difference will physically break the internals of the transmission/differential.

Last point the manual transmission models are much more tolerant to differences in tires than the automatic transmission models. The AWD is very different in each.

Actually only on some and not all AWD vehicles 4 new tires are required.