100% race: No tyre wear scaling in practice, quali and race.
50% race: 50% tyre wear scaling in practice, quali and race.
25% race: 25% tyre wear scaling in practice, quali and race.
100% race: No tyre wear scaling in practice, quali and race.
50% race: 50% tyre wear scaling in practice, quali and race.
25% race: 25% tyre wear scaling in practice, quali and race.
So no matter what the race length you would have the same number of pit stops and the same amount of tyre wear as a 100% race. In a short race the wear rate per lap is going to be much more
Example: If your first pit stop is lap 28 in an 100% race, and at that point they will be let's say 60% worn. In a 50% race they will be 60% worn at lap 14, your first pit stop. Same for the 25% race, this time your first pit stop will be lap 7 and your tyres will be 60% worn
This would be the same for fuel usage too. You always start with a 100% fuel, no matter whether it's a 50% race or a 25% race. It will just burn off twice as quickly in a 50% race, and 4 times as quickly in a 25% race.
This keeps the tyre wear in balance with the weight of the car due to fuel usage. So at that first (or only) pit stop the car will be the same weight, no matter what length race you are driving