why do car manufacturers specify tyre pressures?

[JonnyV]

Thought about this today as i was checking my tyre pressures, Why do car manufacturers specify tyre pressure when they dont know what tyres i may fit when the original ones have worn out ?

 

[JonnyV]

Unless you change the wheels surely you'll be buying the same sized tyre?

But if they didn't say who would? The tyre companies don't know what car they might end up on so you'd be a bit stuck.

Yes, same size tyre. But tyres range from budget remoulds to some goodyear F1 tyres.

 

[JonnyV]

Pressure isn't wheel size dependent, it's about how much air you put in, so does it matter?

i.e. 30psi on a 15inch wheel is the same as 30psi on a 17inch wheel. I guess the pressure required is determined by the size of the car maybe?




How does 30psi on an F1 differ from 30psi on a remould?

I know what your saying, but how can it be that all tyres fitted to my car wether they are budget remoulds or performance tyres take the same tyre pressure?

Im beginning to understand now i think more about it. Its just down to the weight of the car rather than the type of tyre.