just how flat can a tyre be!

[bryan35]

Driving my mates van the other weekend, I though that the offside front tyre looked a bit low, then again it's a van so maybe not. Drove OK.
Still didn't like the look so attached my little cigarette-socket compressor to it. read - 0.0.
Can't be right, maybe the compressor is in some sot of 'relative' mode, so started it up.
After about 1 min it reads 2.0
2.0 is the lowest it will display apparently!

so, I've been driving about with a tyre less than 2psi.

scary!

[tank slapper]

Are you sure it isn't reading in bar? 1 bar = approx 15psi.

[bryan35]

well, it's now got 30 bar in if it has!

nope - definately psi.

[Davi]

It'll only be the bottom bit of the tyre that was 0 psi, the top would have been full up.

My mini pump doesn't even read that low, think it's about 5 psi before it will read.

anyone who think the first part is serious should question their judgement before posting a response...

[Flat in Fifth]

Wasn't a Sherpa was it, I saw one with a front that must have been <2-3psi a few days back.

[7db]

Davi said:

It'll only be the bottom bit of the tyre that was 0 psi, the top would have been full up.

Only when the tyre is warm and all the air floats to the top.

[Nick_F]

If you spin it really fast you can sometimes get the air to even-out all the way round.

[Flat in Fifth]

But what about when the tyre is on a conveyor belt in a wind tunnel?

[CaptainSlow]

hold on...

assuming atmospheric pressure is 14.7 psi then you shouldn't get a lower pressure than that unless there is a vacuum inside?

[neelyp]

CaptainSlow said:

hold on...

assuming atmospheric pressure is 14.7 psi then you shouldn't get a lower pressure than that unless there is a vacuum inside?

That would depend on whether you were measuring the pressure in psia (absolute) or psig (gauge).
Atmospheric pressure is approx 14.7psia or 0psig.

psia is normally only used in processes that operate at a vacuum and a pressure (not at the same time obviously).

Neil

Edited by neelyp on Monday 20th November 16:39

[CaptainSlow]

neelyp said:

CaptainSlow said:

hold on...

assuming atmospheric pressure is 14.7 psi then you shouldn't get a lower pressure than that unless there is a vacuum inside?

That would depend on whether you were measuring the pressure in psia (absolute) or psig (gauge).
Atmospheric pressure is approx 14.7psia or 0psig.

psia is normally only used in processes that operate at a vacuum and a pressure (not at the same time obviously).

Neil

Edited by neelyp on Monday 20th November 16:39

ok I always measure in psia then.

[mcflurry]

Since the tyres are the only thing holding you on the road, shouldn't you have at least looked at them briefly?

[off_again]

bryan35 said:

well, it's now got 30 bar in if it has!

nope - definately psi.

Here is hoping that you are right, because a blow-out could wipe out half of the road....

Ok, I exaggerate, but would be impressive to see what happens....

[pdV6]

CaptainSlow said:

neelyp said:

CaptainSlow said:

hold on...

assuming atmospheric pressure is 14.7 psi then you shouldn't get a lower pressure than that unless there is a vacuum inside?

That would depend on whether you were measuring the pressure in psia (absolute) or psig (gauge).
Atmospheric pressure is approx 14.7psia or 0psig.

psia is normally only used in processes that operate at a vacuum and a pressure (not at the same time obviously).

Neil

Edited by neelyp on Monday 20th November 16:39

ok I always measure in Pisa then.

Blimey - is it safe to drive all the way to Italy on a suspect tyre just to measure it?

[Davi]

[redacted]