I’m Under Pressure

[howardbParticipant @howardb]

Yesterday – Monday, dawned cool and overcast after a cool overnight.

I checked and adjusted the tyre pressures on our Honda estate – 34 psi all round, with a known to be accurate tyre gauge.

I checked that the TPMS readout was displaying the pressures when turning the ignition key on – all ok.

This morning about lunchtime we used the car for a brief errand to the town 3 km away.

Turning the key on I got the usual tyre check reading before starting – left side front and rear 39 and 40 psi –  right side at 34 and 35 psi  ???

Then I realised that today was a sunny morning, quite warm at around lunchtime, the sun shines on the left side tyres, the right side tyres are always in shade due to where the car is always parked.

This explains why the TPMS has always had a tendency to display low pressures on the left side tyres, no matter how careful I am, I have been setting the pressures when the left side tyres are hot from the sun, right side cool in the shade, varying with how hot the sun is.

It looks like I am going to have to consider relative left/right tyre temperatures when checking pressures – measure the temperature of left and right side tyres every time I check and inflate the tyres ?- not something I particularly want to have to do, 5 psi difference is not a good idea to drive on with a 180 hp FWD car.

I am always clinical with motorcycle tyre pressures, too low or too high pressures can result in strange handling on the road, tending to run wide or hooking into corners etc

I found this chart https://askmyauto.com/tire-pressure-vs-temperature-chart/

I will buy an infra-red thermometer and try to establish a relationship between temperature/pressure as it applies to those tyres.

Worth thinking about if you are running a heavy or powerful vehicle – motorhome etc

 

[DiogenesParticipant @diogenes]

I hope you’ll pardon me saying so, but you are overthinking this – you must not set the pressure when the tyres are at different temperatures – do it when they are all cold.

Once set, whatever transient differential may occur due to sunlight, they should return to correct relative values once warmed up by use.

 

[Michael GilliganParticipant @michaelgilligan61133]

A very interesting post, Howard … and a widely-overlooked topic, I am sure.

Have a look at ‘Topinfrared’ … I’ve been very impressed by mine.

MichaelG.

.

Ref for iOS users

https://apps.apple.com/gb/app/topinfrared/id6452017744

[Michael GilliganParticipant @michaelgilligan61133]

Just found this page … which I shall peruse with Coffee

https://www.darksidedevelopments.co.uk/Blog/utilising-thermal-imagingwith-an-iphone/

MichaelG.

[JasonBModerator @jasonb]

Or just get up and check them before the sun gets up, should be fairly even as they would have had the night to stabilise.

[NealebParticipant @nealeb]

Memory tells me that the TPMS on my BMW bike are temperature-compensated. Of course, not likely to see left-right differences, although I could park with one end in sun and t’other in shade!

[JasonB]

On JasonB Said:

Or just get up and check them before the sun gets up, should be fairly even as they would have had the night to stabilise.

… and therefore almost guaranteed to be mis-matched for that high-speed dash to the shops !

Methinks Howard needs a set of tyre-warmers [or a garage?]

MichaelG.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, when I park my car, one side is in direct sunlight for most of the day, but my tyre pressures don’t have any variations, although my credit card is now under pressure as I had all four tyres replaced yesterday plus a new TPMS on the front near side one, which has been inactive for quite some time, these are not cheap @ nearly £80.00 ago.

Regards Nick.

[noel shelleyParticipant @noelshelley55608]

An interesting thread ! That gas pressures vary with temperature is a well known fact. Periodically I check my tyre pressures and drive quite a lot, I have never noticed any significant difference in the handling of the vehicle due to small pressure differences of the type mentioned. First it was alloy wheels, look petty but are notorious for air loss as they age, now I suppose we meed TPMS to worn us of said loss. Fore court air lines, not so common and garages that will repair a puncture = hens teeth.  Before I set off for the day I race round the village 3 times, cornering hard and using violent acceleration to get heat in to the tyres, I then return home to check my tyre pressures with a certified gauge before I start my journey proper – I think not, I’ll take pot luck and be damned ! Noel.

[vintagengineerParticipant @vintagengineer]

You could fill the tyres with nitrogen thus eliminating any moisture in the air which expands with heat. But the tpms are only indicative, I wouldn’t rely on them for total accuracy.

 

[John MCParticipant @johnmc39344]

I agree with Diogenes, the OP is over thinking this, as Jason says, check the pressures before the sun has any chance of expanding the air in the tyres.  When setting a tyre pressure for the vehicle the manufacturers will have taken ambient temperatures into account, this may well make a difference on the race track but not on the road!

Also, “with a known to be accurate tyre gauge”, how is it known to be accurate?

I’ve accumulated several TPG’s, a couple seem to be wildly inaccurate, the others, +/- 2psi seems to cover the accuracy.  Therefore , I use these, assuming the majority are correct.

I tried to make a dead weight type tester to check the gauges.  Didn’t work, too much friction using an O-ring to seal piston/cylinder.  Anyone have any ideas on how to check a tyre pressure gauge?

 

 

[pgk pgkParticipant @pgkpgk17461]

Aren’t forecourt pressure guages supposed to certified regularly ?

I have good correlation between the guage on my compressor, the cheap digital guages I bought on eBay and the toms….unless they’re all out by the same amount.

I’m reasonably paranoid after 4 punctures so drive with tpms displayed. Cold setting is 45psi all round but I’ve had them read 50 just sat in the sun.

Local garage does fix pictures circa £10 last time but a friend recently needed to top-up at a motorway services £1.50 to use the airline is madness

[PlasmaParticipant @plasma]

<p style=”text-align: left;”>Judging by the number of tyre tread belts I see lying at the side of the road these days, not many people keep anything like an eye on their tyre inflation.</p>
These outer tread belts are the remains of a tyre after the side walls have given way under load. Caused by running a tyre seriously underinflated for prolonged periods, the side walls become damaged and denatured due the excessive flex in the wall and increased temperature due to the friction of being constantly stretched and compressed as the tyre rolls.

As soon as the inattentive driver increases their speed on a national or motorway, the weakened sidewalls give up the fight due to higher centripetal force on the tread belt and disintegrate. As NASA call these things they undergo an unplanned disassembly.  The bead and what’s left of the sidewalls stay on the wheel and the tread belt wanders off on its own obeying Newton’s first law until it comes to rest.

The tyre is a complex piece of engineering and deserves to be treated with far more respect than most motorists can summon. After all, on a standard car, four tyre contact patches, each about the size of your hand  are all that connect your vehicle to the tarmac.

It blew me away to learn that most grip afforded by a tyre is as a result of chemical adhesion rather than physical grip.

Michelin advanced tyre course some years ago was a very instructive way to spend a few days in the west Midlands

Mick

 

[pgk pgk]

On pgk pgk Said:

Aren’t forecourt pressure gauges supposed to certified regularly ?

Even if they are, would you trust an instrument  once it’s been driven over, dropped in puddles and used by people who could break hammers?

[bernard towersParticipant @bernardtowers37738]

I dont think the pressure gauge can get driven over!!!

[FulmenParticipant @fulmen]

I suspect that most thread belts come off lorry’s and other heavy vehicles. As the number of wheels increase it becomes harder to notice something wrong with one. And if I’m not mistaken they are often re-threaded which would probably increase the risk of a failure.

[duncan webster 1Participant @duncanwebster1]

Motorway services used to be required to provide a free airline and free water to top up rad and screenwash. I suspect this is still the case but is not enforced.

[Pete RimmerParticipant @peterimmer30576]

Tyre pressures vary significantly during weather changes and according to speed and load and the tyres have a wide margin of safety to allow for just that. I used to run my landspeed bike at 50psi at speeds well past 200mph on the same tyres that were specified at 42psi on the road. The higher cold pressure reduced flex in the sidewalls which in turn reduced the generation of heat and increase in pressure  and it also had the added benefit of reducing rolling resistance at the expense of reduced contact patch and therefore available grip. Not such a huge issue when running only dead straight so long as you kept spin to a minimum.

If I was drag racing or sprinting I would run the same tyre at 15psi or even less to gain extra grip and with a terminal speed up in the high-160’s they did gain a lot of heat from the flexing of the sidewalls  though of course only for less than 10 seconds total running time so there was no opportunity for build up.

My advice is just check them when cold (as in not having been driven) and be content or you’ll go madder than the man with 2 watches. If the TPMS system is having a fit due to the sun warming up one said that is only a temporary issue when the car is parked in the sun. As soon as the car is moving and the tyres get some wind over them then the pressures will stabilize across all four corners. If the issue is that the sun has already warmed the tyres on side for the pressure check then check them when the sun’s not on them, use something to get them out of the sun (for sale sign boards make great lightweight screens that won’t cause damage if you forget they are there) or cool them down with a hose if you must.

With 34 million cars on the road, the majority of which do not get checked from one month to the next us being lazy humans, if it doesn’t look flat or squidgy it’s probably going to cope with it just fine.

[Michael GilliganParticipant @michaelgilligan61133]

I know almost nothing about football[ers], and only a little about Lamborghinis, but given the current forum interest in tyres and speeding, I think it worth sharing this:

https://apple.news/A2nPxLGcgRBiiMJOpdLAfOQ

MichaelG.

[John MC]

On John MC Said:

I agree with Diogenes, the OP is over thinking this, as Jason says, check the pressures before the sun has any chance of expanding the air in the tyres.  When setting a tyre pressure for the vehicle the manufacturers will have taken ambient temperatures into account, this may well make a difference on the race track but not on the road!

Also, “with a known to be accurate tyre gauge”, how is it known to be accurate?

I’ve accumulated several TPG’s, a couple seem to be wildly inaccurate, the others, +/- 2psi seems to cover the accuracy.  Therefore , I use these, assuming the majority are correct.

I tried to make a dead weight type tester to check the gauges.  Didn’t work, too much friction using an O-ring to seal piston/cylinder.  Anyone have any ideas on how to check a tyre pressure gauge?

 

 

“Anyone have any ideas on how to check a tyre pressure gauge?”

Buy one of these as a reference gauge  – guaranteed + or – 1% of final value.

https://www.flaig-praezision.de/en-gb/reifendruckmessger%C3%A4te

Of my selection of tyre gauges, a Motometer in the style of the Flaig, an old Dunlop stick gauge inherited from my father and surprisingly a Parkside/Lidl digital gauge on an inflator are pretty much spot- on compared with the Flaig.

If you buy a Flaig, be aware that the reading hold/reset button has to be pressed to take the reading and then released to hold the reading – not exactly intuitive.

 

 

[PlasmaParticipant @plasma]

<p style=”text-align: left;”>I know almost nothing about football[ers], and only a little about Lamborghinis, but given the current forum interest in tyres and speeding, I think it worth sharing this</p>
Knowing a lot about something  will trust the physical evidence from the scene, tyre marks, gouge marks, debris etc will be far more accurate than human witness evidence.

An eye witness is often presented by the prosecution as the best evidence. Then taken to pieces by the defence to throw their impeccable memory into deep doubt.

Humans often add two and two to come up with six. It’s in our nature to surmise and guess at gaps in our perception or knowledge. For example, a person reports hearing a loud screeching of tyres. He hears a loud thump and turns to see a body lying in the road in front of a stationary car. His brain goes to work, putting together the jigsaw puzzle of sound and vision to arrive at a satisfactory explanation. Clearly the car has braked heavily but was going too fast to avoid hitting the pedestrian. Driver error pure and simple.  In fact, the pedestrian was a suicidal person who jumped from a footway bridge over the road. The driver braked when his body hit the road immediately in front of him and was able to stop before striking the body.

Far fetched? Not really, I have experience of two such incidents in my career. People try to make sense of incomplete information, often with the best of intentions.

Add to that the fragility of human memory and our eye witness becomes even more unreliable.  Memory is not a video recording, it is subject to modification and complete change from its very perception until it is recorded by the police, or in this case the press. How often have you seen an incident only to start questioning yourself a out detail. And when you hear another point of view about the same, incident you will modify and over write the original memory, deleting it from your mind and leaving the adulterated version behind. This process continues with every conversation or news bulletin until you give your statement. When the ever helpful plod will further degrade your recollection by questioning in a biased way “so the vehicke was goi g very quickly then?” A statement not a question, bound to influence the witness.

Finally the truck driver is saying the car was not speeding. We have to question his motives in stating this and his proximity to the incident. He could be attention seeking, many people do when there is a big story to play a bit part in. He could have been overtaken some distance before the crash, allowing the Lamborghini to accelerate quickly to an unsafe speed.

Let the facts and physics do their bit. I worked on a fatal enquiry in that very area of Northern Spain, reviewing the Spanish police report on behalf of the UK coroner.  I found their, scene examinations, methods, and conclusions very sound indeed, certainly well on par with any contemporary investigation.

As an aside a similar request for help was received from the Gibraltar police who asked if we could commment on a series of tyre marks on a section of carriageway.

Obviously with a nice paid for jolly to a sunny destination on the cards we replied that examining the physical marks was essential to be accurate. Sun cream and passport at the ready we awaited arrival of airline tickets.

A parcel indeed arrived from Gibraltar,  slightly larger than we anticipated.

The entire section of road surface, complete with skid marks, had been cut out and lifted onto a semitrailer and was sitting in our car park. Maybe we should have been clearer in our communications.

 

[Michael GilliganParticipant @michaelgilligan61133]

Thanks for the comments, plasma

I was hoping you would respond.

.

I thought it interesting [and no more than that] that an eye-witness had come forward to suggest that the vehicle was being driven reasonably … whereas I guess 90% of the public might presume that two rich young men in a Lambo “must” have been behaving recklessly.

MichaelG.

[PlasmaParticipant @plasma]

Michael. Yes I guess most people would assume that a rich young man in a powerful sports car must have been driving at excess speed.

I work on the old investigation mindset of A B C

Assume nothing

Believe no one

Check everything

So I don’t assume the guy was driving badly or unsafely.

I don’t believe the lorry driver as he is not reliable based on what is in the press

I also don’t believe the witness who was overtaken and stated the Lamborghini suffered a blow out. How could he tell? He simply saw the vehicle lose control. Remember what I said about people trying to make sense of what they see; must have been a puncture to cause the catastrophic loss of control.

I would check, and believe the Spanish police will check, every detail of the scene and vehicle.

I still think that based on the limited information I have seen so far the driver was at fault. Even suffering a tyre failure is something that can be dealt with at reasonable speed. It happens far more often than people think with no fatal consequences.  It also is a popular excuse or explanation for a loss of control, “I had a blow out, I’m a good driver” is often heard. And the vehicle examination reveals four healthy tyres.

Time and a good collision investigation will tell.

[Nicholas FarrParticipant @nicholasfarr14254]

Hi, just out of curiosity, I measured the temperatures of my tyres at about 3.30 this afternoon, starting with the two in full sunshine, I measured them on the sidewall at about midway above the top of the wheel rim, it was no surprise to find the two on the other side were about 10 C lower. I then measure them on the middle of the treads, and the difference wasn’t much more than about 2 C, so I guess the air inside just distributes the heat evenly throughout the wheel and tyres.

Regards Nick.

[howardb]

On howardb Said:

On John MC Said:

I agree with Diogenes, the OP is over thinking this, as Jason says, check the pressures before the sun has any chance of expanding the air in the tyres.  When setting a tyre pressure for the vehicle the manufacturers will have taken ambient temperatures into account, this may well make a difference on the race track but not on the road!

Also, “with a known to be accurate tyre gauge”, how is it known to be accurate?

I’ve accumulated several TPG’s, a couple seem to be wildly inaccurate, the others, +/- 2psi seems to cover the accuracy.  Therefore , I use these, assuming the majority are correct.

I tried to make a dead weight type tester to check the gauges.  Didn’t work, too much friction using an O-ring to seal piston/cylinder.  Anyone have any ideas on how to check a tyre pressure gauge?

 

 

“Anyone have any ideas on how to check a tyre pressure gauge?”

Buy one of these as a reference gauge  – guaranteed + or – 1% of final value.

https://www.flaig-praezision.de/en-gb/reifendruckmessger%C3%A4te

Of my selection of tyre gauges, a Motometer in the style of the Flaig, an old Dunlop stick gauge inherited from my father and surprisingly a Parkside/Lidl digital gauge on an inflator are pretty much spot- on compared with the Flaig.

If you buy a Flaig, be aware that the reading hold/reset button has to be pressed to take the reading and then released to hold the reading – not exactly intuitive.

There are plenty of gauges available like the Flaig, all claiming to be accurate, comes with a certificate that says so.

What I want to do is check the gauges I have.

The way I tried to do this was to make a dead weight tester, the type of device used to calibrate pressure gauges.

The cylinder was 30mm, the piston was sealed with an O-ring.  I applied the pressure with some weight-lifting weights, after calculating weight vs pressure.

Didn’t work, too much friction.  I gradually eased the sealing force on the O-ring.  Couldn’t get it to work, once I had overcome the “stiction” the device would not support the weight.

I’m thinking a piston with no sealing other than some light oil, or maybe a labyrinth type seal?

How do dead weight testers seal their cylinders?

What I thought might be a quick and easy project has turned into something of a head scratcher!

Looking forward to reading the collective thoughts on this.

[Author]

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