Post here all non technical related topics about Formula One. This includes race results, discussions, testing analysis etc. TV coverage and other personal questions should be in Off topic chat.
Well when there are 2 manufacturers, the decision to who uses cwhich tyre in pure economically. One offers a contract, and a team accepts the most interesting.
The FIA regulations also state that in case of 2 manufacturers, each one must be ready anytime to supply 60% of all cars.