"Cold" tyre pressures - define cold?

[Reffio]

Does anyone know at what temp range the "Cold Tyre Pressures" listed on the door shut of the drivers door is?

Having just got the car, I checked the tyre pressures to find they were low (~29PSi all round). So I just whacked them to what was listed on the door. However, seen as it doesn't drop below 30 degrees at night here right now and can be mid-40's plus during the day , I'm guessing I should underinflate them? Or should they be higher due to the fact the tyres are anything from 20 to 30 degrees higher than if I was checking them back home in sunny Scotland?

Any help as always greatly appreciated.

[adsgreen]

Cold really should be 'ambient'.
In general under normal driving tyres increase in temperature by a relatively fixed amount.
So if you start at 10c then tyre air temp may get to say 20c.
If you start at 40c then tyre air temp may get to 50c.
(or a relative percentage increase - cant recall).

The point is that what you usually find is that the tyre pressure will stabilise at a broadly similar level from the same starting pressure at ambient.

if you dd t start with cold/ambient tyre temp then you don't know where on the curve you are.

It's not perfect as drivers and loads are different but it does result in an acceptable hot tyre temp.

[Reffio]

OK thanks. So basically what you are saying is as long as the car hasn't been driven and therefore the tyres are at "ambient temperature" then go for what it says on the door and all should be good?

[adsgreen]

Yup. The "hot" temperature will obviously be different to what you'd get in scotland but the pressure increase should largely be the same. Just remember to pump them up when/if you're back!

[wolfgang]

I've always checked and changed tyre pressures first thing in the morning and before the sun has heated one side of the car.

[Reffio]

OK thanks for the help. Think I'm sorted then but will get up nice and early this weekend to get them double checked and re-set if needed before it gets melting hot during the day again!

[wolfgang]

I have found that if you let the sun heat up one side of the car first and then set the tyre pressures, you could be out by several PSI when all the tyres are back at the same temperature. A few PSI might not sound like much but I can feel the difference in the steering.