why do car manufacturers specify tyre pressures?
- Thread starter JonnyV
- Start date
MonkeyMan said: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.
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it's to do with the weight of the car rather than the make of tyre.
JonnyV said:
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?
JonnyV said:
How does 30psi on an F1 differ from 30psi on a remould?
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Ev0 said:
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.
JonnyV said:
The tyre will have an upper limit pressure that it can be subjected to, this will be way above what any manufactuerer will have set as their required pressure I'd have thought.
Alternatively you could look at it as when buying a new tyre you have to make sure it can take the required pressure, you wouldn't buy one with too low a speed or load rating (I'd hope!).
Ev0 said:
Yeah but you also said its about how much air you put in, which is wrong
as a lower profile tyre will require less air to achieve 30psi than a higher profile tyre...
Same with a stiffer construction tyre compared to a more flexible construction tyre...
You also raise the pressures on a heavy load or at high speed as tyre wall flex raises the temperature of the carcass and can cause the carcass to fail if it gets too hot..
The pressure is dictated by what is required to keep the tyre with a flat contact patch on the road... the heavier the car, the more the tyre will deform at a given pressure...
My 540kg kit car takes 15 psi all around (it has perfect 50:50 weight distribution)..
Were the front heavier, it would require more pressure in the front tyres..
Some tyres need more pressure than others. A tyre with a softside wall will need more pressure to stop it feeling 'soggy'.
The tyre pressures by OEMs just give an idea of what you need to run, they are of course for the recommend tyre aswell.
I run my T1Rs at a higher pressure than Honda recommend. The OEM S02s are very stiff sidewall tyres and are 32/33psi. After a bit of trial and error, I run the T1Rs at 35psi, they felt too soggy at 32psi.
The tyre pressures by OEMs just give an idea of what you need to run, they are of course for the recommend tyre aswell.
I run my T1Rs at a higher pressure than Honda recommend. The OEM S02s are very stiff sidewall tyres and are 32/33psi. After a bit of trial and error, I run the T1Rs at 35psi, they felt too soggy at 32psi.
Dr Who said:
So the pressure in my tyres isn't related to how much air I've put in?
Where have I said the amount of air needed to hit 30psi in one tyre is the same as 30psi in another?
Ev0 said:
So going back to what I said, 30psi in a 15 inch is the same as 30psi on a 17inch, same pressure but hitting that pressure depends on how much air you put in, not the size of the wheel.
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Ev0 said:So the pressure in my tyres isn't related to how much air I've put in?
Where have I said the amount of air needed to hit 30psi in one tyre is the same as 30psi in another?
So going back to what I said, 30psi in a 15 inch is the same as 30psi on a 17inch, same pressure but hitting that pressure depends on how much air you put in, not the size of the wheel.
Man, its not dependant on the volume of air no, you are arguing yourself into a corner...
It is dependant on the pressure, temperature etc etc...
30 psi one day with a given volume can be 29 psi the next day because the temperature of the air and the tyre is different...
So its not just how much...
What about nitrogen?
No air, but still can hit 30psi
