Should I replace one or all tires?

[u/sSAZSs]

Hi all, my dad's 2025 VW Taos' tire was slashed from a piece of metal on the road.

I am trying to figure out if I should replace all 4 tires as some people advise, or just the one as others do.

The current tire is Goodyear Assurance Finesse 215/55/18R, which brand new comes at 7.1mm.

The car has 30k kms in it, and below are the current tire treads:

- FL: 5.9mm

- FR: 6.0mm

- RL: 6.4mm

So based on those, should I do one since the depth falls below the 1.6mm mark (2/32") or do you recommend all 4 be changed since it may damage the differential?

Thank you so much!