No, you buy ONLY one new tyre of similar size say 175/70R13 but brands (or thread patterns) may be different, it's ok.

You pair up the newly bought tyre with the spare unused tyre (different brands doesn't matter, but must be same size)

Now this pair of unused threads (new or old) tyres, put in rear or front ?

I recommend to put in the rear axle for preventing hydro planing during heavy rain at high speed cornering.

The other 2 units 80 % used tyres be installed at the front axle, with the 3rd unit of 80% used tyre keep as spare unit in car boot .

The above arrangement will used up the spare tyre within 10 year life span.

Note:I'd a 12 year old unused tyre couldn't be reused cos it was 'dented' and slightly out of shape in the car boot.

This post has been edited by zeng: Jun 21 2018, 12:48 AM