tyre pressures - and apply when hot or cold?

[cammy71]

Hi All, looking for some advice. I am running Goodyear F1 Asymmetrics 235/40 on rear and 225/35 on front. What should these pressures be as I'm sure dealer said 24s all round. However, when checking this morning, 1st time since purchase, after 20 mile motroway run pressures were reading 26 front and 28 back. Do pressures apply to hot or cold, and whatever the answer what are the adjustments to be made either way.

[LaserTam]

Certainly should be cold when checked. 24 is generally about right

[cammy71]

Cheers LaserTam. So if measuring when warm, would this 1 or 2 psi higher i.e. 25/26 to be set on the machine?

[darkmark07]

Difficult to say what the pressure should be when warm.

Best bet if you must adjust them while hot is to slightly over-inflate then wait until cool and double-check the pressures using a dial gauge, deflating as necessary.

I bought one from eBay for about £20 - a worthwhile investment as these cars are super-sensitive to tyre pressures and it pays to get them right.

For example: http://cgi.ebay.co.uk/Tyre-pressure-gauge-Longacre...

ETA - 24psi all round is the way forward...

Edited by darkmark07 on Friday 23 April 13:13

[5yearstobuyatvr]

According to factory manual 28 psi allround

[Barry Ashcroft]

5yearstobuyatvr said:

According to factory manual 28 psi allround

Already been discussed a million times that 28psi is too hard much nicer drive at 24psi

[LeeT350c]

24psi all round.

If you want them to stay at 24 warm or cold get down your local Kwik fit and ask them to deflate them and inflate with nitrogen.

"other tyre fitters are available"!!

cheers. Lee,

[darkmark07]

LeeT350c said:

...nitrogen...

Um, really? Boyle's law doesn't apply to Nitrogen then?

[LeeT350c]

darkmark07 said:

LeeT350c said:

...nitrogen...

Um, really? Boyle's law doesn't apply to Nitrogen then?

Of course and you are hoping that the nitrogen used is as pure and 'dry' as possible. There will still be an increase and decrease but not as much as the st wet moist air they normally add as the water traps are rubbish.

[Targarama]

Barry Ashcroft said:

5yearstobuyatvr said:

According to factory manual 28 psi allround

Already been discussed a million times that 28psi is too hard much nicer drive at 24psi

I've never owned a car so sensitive to minor pressure changes.

28psi = scarey handling, far to sensitive. I am not sure why the factory decided to recommend this higher pressure in the later years. In my experience 26psi = OK for long motorway runs, not ideal on twisty roads. 24-25psi much much better.

All checked when cold.

[cammy71]

Thanks all for your advice and responses, will check when cold and when warm and look at the variance. Looks like I'll be going for the 24-26 cold to warm range.

[darkmark07]

LeeT350c said:

darkmark07 said:

LeeT350c said:

...nitrogen...

Um, really? Boyle's law doesn't apply to Nitrogen then?

Of course and you are hoping that the nitrogen used is as pure and 'dry' as possible. There will still be an increase and decrease but not as much as the st wet moist air they normally add as the water traps are rubbish.

So what benefit does filling your tyres with Nitrogen over normal air (which is, what 80% ish Nitrogen anyway) give you then?

[Barry Ashcroft]

darkmark07 said:

LeeT350c said:

darkmark07 said:

LeeT350c said:

...nitrogen...

Um, really? Boyle's law doesn't apply to Nitrogen then?

Of course and you are hoping that the nitrogen used is as pure and 'dry' as possible. There will still be an increase and decrease but not as much as the st wet moist air they normally add as the water traps are rubbish.

So what benefit does filling your tyres with Nitrogen over normal air (which is, what 80% ish Nitrogen anyway) give you then?

It's lighter

[TheArb]

Targarama said:

Barry Ashcroft said:

5yearstobuyatvr said:

According to factory manual 28 psi allround

Already been discussed a million times that 28psi is too hard much nicer drive at 24psi

I've never owned a car so sensitive to minor pressure changes.

28psi = scarey handling, far to sensitive. I am not sure why the factory decided to recommend this higher pressure in the later years. In my experience 26psi = OK for long motorway runs, not ideal on twisty roads. 24-25psi much much better.

All checked when cold.

you'll like this. Picked up the car from servicing last month after I had been away abroad for a few weeks. Ride seemed a bit hard. After a couple of days of bone jarring driving and losing all my dental fillings I took it along to a service station to check the pressures. All absolutely identical at.................39psi. Oh the relief of getting back to normal afterwards.

[Cerberus90]

darkmark07 said:

LeeT350c said:

darkmark07 said:

LeeT350c said:

...nitrogen...

Um, really? Boyle's law doesn't apply to Nitrogen then?

Of course and you are hoping that the nitrogen used is as pure and 'dry' as possible. There will still be an increase and decrease but not as much as the st wet moist air they normally add as the water traps are rubbish.

So what benefit does filling your tyres with Nitrogen over normal air (which is, what 80% ish Nitrogen anyway) give you then?

The Nissan GTRs tyres are filled with nitrogen from the factory, because its apparently more stable.


Heres a few links from the first page of a google search :

Clicky

[url]Clicky|http://www.vcars.co.uk/news/generic-trend-stories/drivers-urged-to-consider-nitrogen-for-tyres-407.html[url]

[kcc]

TheArb said:

Targarama said:

Barry Ashcroft said:

5yearstobuyatvr said:

According to factory manual 28 psi allround

Already been discussed a million times that 28psi is too hard much nicer drive at 24psi

I've never owned a car so sensitive to minor pressure changes.

28psi = scarey handling, far to sensitive. I am not sure why the factory decided to recommend this higher pressure in the later years. In my experience 26psi = OK for long motorway runs, not ideal on twisty roads. 24-25psi much much better.

All checked when cold.

you'll like this. Picked up the car from servicing last month after I had been away abroad for a few weeks. Ride seemed a bit hard. After a couple of days of bone jarring driving and losing all my dental fillings I took it along to a service station to check the pressures. All absolutely identical at.................39psi. Oh the relief of getting back to normal afterwards.

Who does your servicing.

[tail slide]

Nitrogen, or alternatively dry-air, filling is something they found out in racing years ago.

It's the water content of normal air that's the problem, which increases in pressure when heated, like steam does. Particularly happens on a track day when your tyres can quite quickly go to 90C and above.

Air is mainly nitrogen anyway, but the elimination of oxygen/water vapour means the tyre pressure stays much more stable when heated.

[5yearstobuyatvr]

Surely the factory, with all their testing knows best!

Barry Ashcroft said:

5yearstobuyatvr said:

According to factory manual 28 psi allround

Already been discussed a million times that 28psi is too hard much nicer drive at 24psi

[Targarama]

5yearstobuyatvr said:

Surely the factory, with all their testing knows best!

Barry Ashcroft said:

5yearstobuyatvr said:

According to factory manual 28 psi allround

Already been discussed a million times that 28psi is too hard much nicer drive at 24psi

Are you running your Tamora at 28psi? Try 24psi on your favourite twisty road and report back.

[darkmark07]

Sounds like snake oil to me tbh. Unless you're a real track star - and even then I struggle with the whole concept from the point of view of basic schoolboy physics - the expansive characteristics of gases are not so different, and as pressure changes are dependent on temperature differences from absolute zero (-270 something degress C).

I concede, happily, that it is better to have a more stable / common mixture between all tyres, but even then the pressure front / back and left / right would have to be specifically tailored to each track to ensure that the tyres come up to operating temperature together and remain at optimum pressure when when at optimum temperature in order to give the longest life / best grip. Something that I'm sure happens in the higher end of motorsport where tenths / hundredths / thousandths of seconds really count, but for regular, even spirited road use?

Really?