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MG MGF Technical - Tyre pressure - temperature relationship

Hi guys

We all know how the handling varies greatly with tyre pressure..

i think i am right in saying the 28rear/26front psi setting assumes an air temp of 20c..

We all know how hot its been lately and some mornings its been 25c by 9am..

The air temp was 30c on some days so the air temp in hot running tyres was probably well above that.. so the air pressure would increase but by how much?

Does the softening of the tyre due to the heat compensate for the increased pressure?

If i remember rightly 'boyles'law has something to do with heat/ pressure relaionship..

Anyone remember their physics lectures??

Stu
Stu

While trying to source window lift relays, I contacted the malaysian compnay linked to on Dieter's web-site.

They said they no longer do the window relay, but offered a variety of other "toys".

Can't find the link, but here is someone offering a similar gizmo.

http://www.tyresave.co.uk/smartire.html

paul weatherill

Stu

Your getting confused;-) Boyles law required constant pressure. Use Charles law for a temperature volume relationship. ie v1/t2=v2/t1

Then you can derive p1v1/t1=p2v2/t2

Hope that helps:-)

Neil
Neil Stothert

Neil...>> Hope that helps...

ABSOlutely, Mate!!!!

The only law I can still remember is:

The Angle of Dangle = Lust times Thrust assuming the Urge remains constant.

...but I can't remember who's law it is!

(Not true really...I can still recite Newton's jobbies word for word!! How useful is THAT?)
SimonKE

<<How useful is THAT>>

Very useful when you think that in our cars we are sometimes stationary, can accelerate and sometimes hit other objects:-)

Neil
Neil Stothert

Nice one Neil

I know i should have paid more attention at those dam lectures!! LOL The only two laws i could remember were Boyles and Daltons, completely forgot about Charles law...

I'm a diving instructor too!! I think all those deep dives have melted some of me brain cells!!

Thanks

Stu
Stu

UNBELIEVABLE !!....TALK ABOUT BLOODY ANORAKS ??...... Every driver knows the importance of tyre pressures for handling and tyre lifespan but do we really need to get obsessed with outside temperature now ?.....whats it gonna be next?.....must tell the insurance company its rather warm today, might alter the handling on the car and invalidate my cover..get a hobby or better still a life !!!
Max Headroom

Max

I think you'll find this is MGF Technical and that there are some people who wish to have a greater understanding of their cars rather than simply discussing if the colour looks good. Personally I don't think you should be allowed to drive unless you have a technical understanding of how the car works.


Neil
Neil Stothert

Oh no......off we go.....Handbags AGAIN chaps!!!!!
SimonKE

Can't resist this. If the tyre volume stays the same, the pressure will increase by about 0.35% per degree C temperature rise. Expansion of the tyre will reduce this pressure increase. Since a tyre that runs at speed for any length of time gets quite hot, as will the air inside, the ambient temperature increase has an insignificant effect compared to this.
Brian

Personally I don't think you should be allowed to drive unless you have a technical understanding of how the car works and have driven a PTW for at least 12 months.

John Ponting

Or for the first 12 months you could only drive a car without seatbelts, airbags or abs fitted.
Neil Stothert

And what about nitrogen inflated tyres? Why are that so recomendable? Has a lower coefficient of dilatation?
Spinder00

This thread was discussed between 25/07/2003 and 28/07/2003

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