OT: Tyre pressures

[Donwill]

Having recently purchased a new (S/H) car, I was checking tyre pressures and found them to be over the manufacturers recommended pressure by some 10lbs or so. I checked on some tyre sites and saw their recommendation that they should be adjusted when "cold" ?!! what does that mean I thought and after a chat with friends some thought 15degC others 20degC.

To cap it all the michelin site says: "They must be checked when the tyre is cold (By cold we mean the ambient outside temperature where the tyre is to be used)." I hope to drive to Spain in the near future and I'm almost certain that the air temperature can vary by about 25deg through the day.

Any thoughts? Don

[Adrian]

"Donwill" gurgled happily, sounding much like they were saying:

That's nowhere NEAR as much as the temperature of the tyre (and air within it) can vary between unused and after-a-long-hard-thrape.

[lofty]

I drive to the costa del Sol every year, towing my caravan, I always inflate the tyres to the specification in the handbook. no problems.

Lofty

[Dave Liquorice]

10psi above the recomended is a bit high but don't take the book pressures as gospel. If I run my car at the book pressure on the front you see the characteristic wear signs of under inflation within a few thousand miles. Bung them up by a couple of psi above the book and tyre wear is even across the entire tread.

The best way to check for correct inflation and wheel alignment is to keep an eye on tyre wear. They should wear evenly all the way around and across the tread anything else indicates something amiss with inflation or alignment. Alignment can affect rear wheels as well.

It means check them when the tyre and air inside it is at ambient not warm or hot like they will be after you have been driving for a while.

It's not that critical, I noticed a couple of psi different between mid winter and sub zero temps and a warm spell with it over 15C. The tyre and air inside will be much hotter and have a higher pressure when driving, particularly at speed or hard.

[ARWadworth]

Is that front or rear wheel drive? I have noticed this more on RWD cars.

That is exactly what it means.

I have thrashed a fully loaded car from South Yorkshire to Slovakia a few times. The important thing was to inflate the tyres to the manufactures spec for the journey there and back and deflate to normal pressure for the driving done whilst on holiday with no load.

Adam

[GGJ]

By cold , they mean that the caravan has not been towed, same as with a car its best to check your tyre pressure before you drive any distance as it does not take long before the temperature of the tyre will rise causing the pressure in the tyre to rise as well. Give it a try, measure the pressure in the tyre of your car, take it for a

10 mile run and then measure the pressure again it should have gone up a bit.

GGJ

[Stephen Howard]

Here's a good place to start ( or end up ).

[Dave Liquorice]

4 wheel drive. B-) It's well known that the book pressure for this car is "wrong".

[Donwill]

Excellent site, thanks for the link

Don

[jal]

As another person has said (incidentally creating a separate thread by omitting the "OT:"):

"Cold" tyres are purely and simply tyres that haven't been driven anywhere. If you get the pressure right at this point, the immense technology behind tyre manufacture will take care of all other factors that you encounter between here and Timbuktu.

john

[Invisible Man]

The tyres should be at the correct pressure for the ambient temperature in which they are operating. This is when they have not been run for a few hours and are not in direct sunlight which would warm them up and increase pressure. If you go from somewhere around 0C to somewhere around 45C the pressure will be too high. If you live somewhere like a desert where temperatures vary hugely between day and night set them for the temperature at which the vehicle is most used. I find I have to put air in my tyres as the temperature in the UK drops as we head into winter.

[terry]

BTW there is, apparently, an outfit here, even in this relatively milder part of Canada, who will install nitrogen in ones tyres. Claiming that it does not expand contract so much (or at all?).

Also hearing, somewhere, that automatic pressure sensors from each wheel to a car's computer will eventually become mandatory. Another gadget!

However yesterday saw car that was driving on an almost flat rear tyre and two other low tyres and when I mentioned it to the driver he just said "Yes I know"! And then drove off at normal speed! Dangerous buddy.