Dansk English
Some people change all four tires each time they change tyres. Others change two at a time because the free-running wheels do not wear as quickly as the working wheels. I got curious about how much money you'll save by changing two at a time. It must be measured against the added inconvenience by having more and irregular tyre changes.
PS. All units are Danish, but just imagine that they're not.
(Only integer numbers are allowed.)
Driving per year 6'000 km. Working wheels last 54'000 km. Free-running wheels last 60'000 km. One tyre costs 2'000 kr. After 540'000 km. all wheels must be changed whether you change two or four at the time.