Tire replacement: 2 or 4 tires?

I have a 1999 Toyota Corolla and have just one tire that is getting bald. The tread on the rest of the tires is fine. I am wondering if I will need to replace all 4 tires or whether it would be OK to replace just 2? Any help is greatly appreciated!

4 is optimal for best balance of traction in extreme conditions(eg winter or emergency).

However 2 brand new ones is okay most of time however they must installed on rear not front.

What is “just fine” 4/32" looks ok but if you need one tire and the others are down to this, replace all 4. If the tread is 7/32 or better, then just two are needed. If 9/32", then only one tire is needed.

But, why is one tire bald and not the rest? If you don’t know the answer, then you better have a front end specialist look at it with the old tires on it. The tires will give him clues.

All traction discussions aside, you won’t cause any mechanical problems by just replacing one. Some tire places will install three different size tires on a car like yours and cause nothing to break until you have to make a panic stop or drive on a wet highway… One new tire won’t cause any problems.