Tires: the relation between tires width and car speed, diameter tire, maximum horsepower

Question
i read someplace that the a car's top speed is closely related to the type of tire it uses.
they said that if you put 145R13 type tires on a renault 12, which has a top speed of 140 kmh using 155R13 tires (standard), it will go at 145 kmh. My question is: why does top speed increase if you use narrower tires?

Answer
A tire's size has no relationship on a vehicle's top speed.

However, a tire's diameter does have an effect on the overall relationship between the speed of the engine and the speed of the vehicle.  So if a vehicle reaches its top speed before the engine reaches its maximum horsepower, then a smaller diameter tire allow the vehicle to go faster.  But changing gearing in the car could accomplish the same thing.

Hope this helps.