Tyre pressure vs Temperature

Submitted: Saturday, Mar 19, 2016 at 19:14
ThreadID: 131877 Views:3331 Replies:10 FollowUps:31
This Thread has been Archived
Hi, I have the formula for the pressure change due to tyre temp change, and have recently bought a set of TPM'S.

Can any one give me their experience in what sort of maximum temperature you would normally expect to see if the start ambient temperature was say 30°c (NW of WA).

Thanks.
Back Expand Un-Read 0 Moderator

Reply By: TomH - Saturday, Mar 19, 2016 at 19:37

Saturday, Mar 19, 2016 at 19:37
My fronts werent far above ambient and the rears when towing were up to 15 or so above ambient.
However when I started the trip I had a full width stoneguard across the rear and the rears got up to 65 deg on a 25 deg day. Took it off and never had any more troubles.

Worked on 6lb change of pressure and had temp warning set at about 55deg.

Be aware that the tyres on the sunny side will run a bit hotter than the shady side.

Didnt seem to make much differenece where we were.

Was on a Landcruiser
AnswerID: 597560

Follow Up By: Member - johntoyo - Saturday, Mar 19, 2016 at 20:08

Saturday, Mar 19, 2016 at 20:08
Thanks Tom. No indication in the set up manual what to expect so wanted an idea as to what set the max at.

John
0
FollowupID: 866601

Follow Up By: Member - johntoyo - Saturday, Mar 19, 2016 at 20:13

Saturday, Mar 19, 2016 at 20:13
Tom, take your point on the full width rear stone guard as I have heard that before. On my LC200 I have extended length individual rear stone guards and run a stone stomper.

John.
0
FollowupID: 866603

Follow Up By: TomH - Saturday, Mar 19, 2016 at 21:44

Saturday, Mar 19, 2016 at 21:44
Yeah mine had a gap in the middle but still heated the tyres and the diff up> Was a mention on Lcool where 100 ser had blown diffs due to overheating because of full width stone guards. I only got one mark on the van from a stone.
0
FollowupID: 866610

Reply By: Member - shane r1 - Saturday, Mar 19, 2016 at 19:59

Saturday, Mar 19, 2016 at 19:59
I have more than twenty years of tyre retailing, and prior to that took good care of my own tyres.
I wouldn't be worrying about temperature too much, providing you run the correct pressures and aren't grossly overloaded.
The only advice I give is , if you have to travel in hot weather just lower your speed 20kph.
I have seen plenty of trucks on the east west run blowing tyres in hot weather, but the drivers that backed off the speed had very little trouble, or some pulled up until it cooled down.
Cheers Robbo
AnswerID: 597561

Reply By: Robin Miller - Saturday, Mar 19, 2016 at 21:39

Saturday, Mar 19, 2016 at 21:39
Rule of thump is about 6 or 7 degrees rise for every 1 psi increase when driving.

You can work it out though !


Its a direct relationship between temp and pressure, if one goes up 10% , so does the other !

So what you do is note the tyre pressure change from cold to hot running
and that will tell you the exact tyre temperature you should read.

There is a catch and that is you have to use absolute units for temp and pressure i.e. Kelvin not centigrade.
Also, if you read a pressure as 30psi , its really 30+15=45 absolute, where 15 is air pressure at sea level.


E.G.

If tyres were cold (say 30c) and pressure was 30psi then absolute pressure is 30+15=45 and absolute temperature is 30c=303k.

if after driving you measure tyres as 34psi then absolute pressure is 34+15=49.
49/45 psi = about 9% increase.

Now rule is that the temperature goes up the same 9%.

So temperature is 303+9% of 303 = 330k = 57c

i.e. 4 psi increase causes a 27c temp increase (in this example, and not a bad general guide)
Robin Miller

Member
My Profile  Send Message

AnswerID: 597564

Follow Up By: TomH - Saturday, Mar 19, 2016 at 21:52

Saturday, Mar 19, 2016 at 21:52
Well I had my fronts at about 35 and rears at 40 cold and they came up 6lb when towing Temps didnt go off the scale and with alarm set at 55 didnt have any trouble.

The main thing is if not hard enough will get disproportionally hot and give trouble. Using the 6lb rule I did 50,000k and never had a puncture or any tyre problems in the Cruiser.

The van which had Dunlop LT 's had two delaminate, something not unknown to Dunlop tyres.

Its actually rule of thumb "a broadly accurate guide or principle, based on practice rather than theory".LOL
0
FollowupID: 866611

Follow Up By: Member - johntoyo - Saturday, Mar 19, 2016 at 22:29

Saturday, Mar 19, 2016 at 22:29
Thanks Robin.
Yes I got all that therory from Wikipedia, (ideal gas law) and was aware that it was based upon the Kelvin unit. There is also a very good chart with conversions etc. which can be printed out, and what I am going to do for the first trip.

But as Tom says, lets see what actually is seen. I just wanted a starting point and both posts get me there thanks.

My wife says she is going to do all the driving while I can watch the now TPM, Scangauge and CB etc.

John.
1
FollowupID: 866615

Follow Up By: Dion - Saturday, Mar 19, 2016 at 23:08

Saturday, Mar 19, 2016 at 23:08
Good ol Wiki, what a marvelous reference.
0
FollowupID: 866619

Follow Up By: Robin Miller - Sunday, Mar 20, 2016 at 09:43

Sunday, Mar 20, 2016 at 09:43
I also meant to add that some types of Tmps systems are quite inaccurate for temperature.

Generally the small screw onto your valve types.

I have such a system and the sensor isn't very well connected to the warm air inside the tyre and in my case the temperature won't rise hardly at all above ambient.

So its good to do a test like I put and hence check that your system is reading ok.

Robin Miller

Member
My Profile  Send Message

0
FollowupID: 866627

Reply By: Les - PK Ranger - Saturday, Mar 19, 2016 at 22:12

Saturday, Mar 19, 2016 at 22:12
Just a thought, it's interesting to realise we still resist metric when it comes to tyre pressure, staying with PSI readings.
AnswerID: 597565

Follow Up By: TomH - Saturday, Mar 19, 2016 at 22:26

Saturday, Mar 19, 2016 at 22:26
Probably because we are old and its easier to work in Lbs than Bars or whatever else grabs you
0
FollowupID: 866613

Follow Up By: Les - PK Ranger - Saturday, Mar 19, 2016 at 22:29

Saturday, Mar 19, 2016 at 22:29
For sure, wouldn't even know what bar or kpa was as normal substitute for the regular psi pressures :)
0
FollowupID: 866616

Follow Up By: Member - shane r1 - Sunday, Mar 20, 2016 at 08:45

Sunday, Mar 20, 2016 at 08:45
Even in the tyre industry psi is the main measure
0
FollowupID: 866624

Follow Up By: Allan B (Member, SunCoast) - Sunday, Mar 20, 2016 at 09:37

Sunday, Mar 20, 2016 at 09:37
Because USA is dominant in the tyre industry.
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 866626

Follow Up By: Les - PK Ranger - Sunday, Mar 20, 2016 at 12:54

Sunday, Mar 20, 2016 at 12:54
True, wonder then why we don't use tire ?? :)
1
FollowupID: 866637

Follow Up By: Allan B (Member, SunCoast) - Sunday, Mar 20, 2016 at 12:58

Sunday, Mar 20, 2016 at 12:58
Can if you want to Les.
Me?.... I'm re-tired. lol
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

2
FollowupID: 866639

Reply By: Allan B (Member, SunCoast) - Saturday, Mar 19, 2016 at 23:43

Saturday, Mar 19, 2016 at 23:43
.
The considerations that Robin has described are essentially correct except that the interaction is opposite to his description.
The heat is generated by the flexing of the tyre and this rise in temperature causes an increase in the pressure of the air. So a 27c temperature increase produces a 4psi increase.
But certainly, a indication of pressure increase is evidence of tyre temperature increase.
Clearly, raising the tyre pressure by compressor inflation does not increase its temperature if the delivered air is not hot.
Although tyres are clearly rated with their maximum pressure it is not so easy to determine the manufacturer's recommendations for maximum temperature. I would get concerned if my monitors indicate more than 65c but that value is speculation on my part and represents about 6psi increase.
And one other point. An indication of tyre temperature can only be reasonably accurate if the sensor is internal. Sensors mounted externally on the valve stem will indicate far from the true tyre temperature and certainly lower. Using such temperature indication could result in unsafe practice.
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

AnswerID: 597569

Follow Up By: Sand Man (SA) - Sunday, Mar 20, 2016 at 08:34

Sunday, Mar 20, 2016 at 08:34
Allan,

You have made a very accurate and important point re internal vs external TPMS sensors.

In my experience, not only is the temperature inaccurate when using external sensors, but so is the pressures.

I took great care insuring that the pressures on all four tyres were identical using the pressure gauge (doesn't matter what the pressure setting was) and all four tyres showed a discrepancy of several psi.

On my last outback trip, the two nearside tyre sensors lost connectivity with the monitor and rendered the whole TPMS system totally unreliable.
My choice of a cheaper TPMS utilising external sensors was justified purely on the basis of a sudden deflation of a tyre enabling me to pull up before irreparable damage was done, but when the bloody things are not registering with the monitor, then the whole system is useless.

External sensors are also a PITA (when using locking rings) when you need to air up and down when changing to a different road/track surface.

The sensors were removed and are still rattling around in the console somewhere, along with the monitor.



Bill


I'm diagonally parked in a parallel Universe!

Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 866623

Follow Up By: Allan B (Member, SunCoast) - Sunday, Mar 20, 2016 at 10:37

Sunday, Mar 20, 2016 at 10:37
.
Hi Bill,

I spent many years in process measurement & control. I experienced the difficulty of accurate temperature measurement and how much easier it was to measure pressure.

But there is a bit more to it than just the physics. My first monitor was a Tyre Dog external. One sensor failed after 200km, the second in the next 100km. On a bitumen highway! I dumped the system and substituted Inawise internal monitors thus gaining the bonus of sensible temperature indication. I do not know the failure reason of the Tyre Dog externals but do understand the manufacturing difficulties of packing the electronics and a replaceable battery into such a small package hanging on the end of a valve stem. I should have known better!

The Inawise system has performed flawlessly and has alerted me to low pressure on two occasions which is its prime function. However, I have found it to be very useful in indicating a valid temperature reading of the tyres. When running at reduced pressures, the pressure rise due to temperature will not even approach the manufacturer's pressure limit but the temperature may increase dramatically and I am happy to be able to monitor that.

The treatise offered by Robin above is not entirely correct but may be useful over small changes. Where it fails is that it does not take into account that the air volume is able to expand with pressure rise due to the flexibility of the tyre. The consideration now becomes much more complex than Robin's simple exposition. Certainly some correlation can be drawn but the pressure rise will not be a simple or linear relation to the temperature increase. My problem is ascertaining what the manufacturer of a particular tyre considers to be its maximum temperature.

Despite all that, the presence of a reliable pressure alarm, whether internal or external, is of great benefit particularly on rough tracks where a deflating tyre is not readily detected by vehicle behaviour. It provides an alert before further tyre damage.
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

1
FollowupID: 866629

Follow Up By: Member - Terry W4 - Sunday, Mar 20, 2016 at 17:36

Sunday, Mar 20, 2016 at 17:36
Allan

I have the tyre dog 6 sensor TPMS (2 for the camper) and have had no problems over 50,000 kms. It reads fairly accurately. I hade the temps set for 50 degrees last years and they went off going down the Clyde Mountain with the trailer on the back and lots of braking - the ambient air temp was about 35. I have now reset at 60.

But given Canberra's ambient air temperature is about to get down to 12-15 in the next few months I might drop again to 50.

0
FollowupID: 866645

Follow Up By: Allan B (Member, SunCoast) - Sunday, Mar 20, 2016 at 19:35

Sunday, Mar 20, 2016 at 19:35
Yes Terry, I'm sure not all tyre Dogs fail, just the one I purchased.... and Sand Man's.

Your Tyre Dog going into alarm "at 50 degrees and lots of braking" suggests that they are bearer at detecting brake temperatures than tyre temps. Believe me mate, it is impossible to obtain any meaningful tyre temperature from a sensor mounted externally on the valve stem.
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 866647

Follow Up By: Member - Terry W4 - Sunday, Mar 20, 2016 at 20:21

Sunday, Mar 20, 2016 at 20:21
Agree Allan.

It was in fact measuring the temperature of the alloy rim. Which is fine by mne because there must be a correlation between, brake temp, rim temp and then finally tyre. But I am only really interested in tyre pressure.
0
FollowupID: 866648

Follow Up By: Member - Boobook - Monday, Mar 21, 2016 at 07:40

Monday, Mar 21, 2016 at 07:40
Some people prefer the internal units and others like me, the external sensors.

There is no doubt that the internal ones will give a much more accurate reading of temperature. The pressure reading will be exactly the same however, To me this isn't a large problem because temp is a lagging indicator of a problem, and a slow one at that. An over temp alarm shows that something has been wrong for a long time, usually low pressure.

Internal units have other disadvantages that far outweigh the temperature IMHO of course.
1)They are not suitable for swapping out wheels, a big problem when touring with multiple spares.
2)Most ( but not all) won't accommodate 6 or more tyres.
3)The batteries are sealed, and despite the claim that they last 5 years plus, my experience has been that I had to buy all new sensors after 2 1/2 to 3 years. Bang $300 plus for new batteries
4)They can get damaged when changing tyres ( especially outback or DIY)

Externals of course have
-a less accurate temp display
-could be stolen in theory but it hasn't happened to me in 8 years.
-have to be taken off to adjust pressures. ( bu tso does a dust cap)
-can damage rims ( this has happened to me)

I now have the ABR sidewinder ??? 22 which are brilliant. The sensor batteries ran out about 5 months ago. I replaced them and they have been under water including salt water and they are fine. Their only downside it that the sensors could be a little smaller.

Each to their own, I have read bad reviews about the Tyre Dogs leaking after battery replacement ( and poor range) so agree with Allan about them.

Also regarding the original topic, I agree that a simple use of the PT law does not apply to tyres. Apart from the tyre changing shape as Allan points out ( which ignores one constraint in the
PT Law), Air is not a simple gas, and in most cases contains a large amount of moisture in the form of humidity. Anyone that owns an air tank will testify to the amount of water in what would be considered dry air.

I have no idea what the formula for that is, but I do know it ain't gunna be linear.

1
FollowupID: 866651

Follow Up By: Allan B (Member, SunCoast) - Monday, Mar 21, 2016 at 09:14

Monday, Mar 21, 2016 at 09:14
.
As you say Boobook, "each to their own". I just feel more comfortable with them tucked internally out of harm's way.

Your internal sensors batteries expired after 3 years? Pretty poor. I wonder what brand they were?
My Inawise sensor batteries are rated at 7 years. They are now at 6 years and I am about to replace tyres so will replace the sensors at this time. Yes, maybe $300 but compared to what I spend on fuel, maintenance and tyres, I consider it good value 'insurance'.

I have some difficulty following a couple of your points.........

"not suitable for swapping out wheels"?? My Inawise system displays only 4 wheels but both my spares are fitted with sensors and can be selected for display when placed in use.

And "most...won't accommodate 6 or more tyres". Mine will as above.
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 866654

Follow Up By: Member - Boobook - Monday, Mar 21, 2016 at 11:42

Monday, Mar 21, 2016 at 11:42
Yeah I was kind of vague on the spares thing.

What I meant was that at times I go away with 9 wheels.

4 on the vehicle, 2 on the trailer and 3 spares. My vehicle and trailer wheels are identical. Often by the time I get home the wheels are in completely different positions to where they started.

I own 6 sensors and just make sure they go back on the wheel that is in the right position after a changeover. I think that I would need 9 sensors to accommodate that with internals, and they would have to be reconfigured every change ( which can be a couple of times a day when things are bad.)

But the worst part for me is that you need to buy 9 new sensors when the battery runs out. I bought 10 batteries for $25.

Make sense?

Also I should mention that it measures exactly the same pressure as my Jamec Pems inflator which is individually calibrated and certified to 0.3PSI.
1
FollowupID: 866660

Follow Up By: Allan B (Member, SunCoast) - Monday, Mar 21, 2016 at 13:09

Monday, Mar 21, 2016 at 13:09
Makes perfect sense Boobook. Thanks.
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

1
FollowupID: 866666

Reply By: jadatis - Sunday, Mar 20, 2016 at 04:20

Sunday, Mar 20, 2016 at 04:20
Also determined the formula for it and even made spreadsheet for it, but lately made some lists.
In kPa/ degr C

But also in psi /Fahrenheit


Use them like this
What was ambiënt temp when measured cold ( inside tire temp =outside tire temp)
Seach this pressure in the list after the temp .
Then what is ambiënt temp ( outside tire temp) when driving.
Find wich pressure it gets cold at that temp in list.
Asume a temp rising of 27 degr C/47 degr F when driving 90km/55m/h and highen up ambiënt when driving by that.
Look at this temp what the pressure will be .

Greatings from a Dutch Pigheaded Selfdeclared Tyrepressure-specialist
Peter
AnswerID: 597571

Reply By: Batt's - Sunday, Mar 20, 2016 at 23:31

Sunday, Mar 20, 2016 at 23:31
Ah the rule of thumb and formulas never heard of it yrs ago just seems to be a recent thing which has snowballed out of control these days just like the 4psi rule. To many variables involved tyre width, rolling diameter type of tyre eg road, A/T mud etc type of vehicle weight of vehicle, whether you're towing etc etc. Just pump your tyres up to the pressure recommended by a tyre outlet and adjust to suit when required. I have noticed over the yrs that depending on conditions my tyres will usually increase pressure by 2 lb to 4 lb even on the hottest days but that's just me checking tyre pressures and not trying to complicate things with other ideas that have been circulating around kiss.
AnswerID: 597591

Reply By: Member - shane r1 - Monday, Mar 21, 2016 at 08:14

Monday, Mar 21, 2016 at 08:14
As per my earlier reply, you don't need to stress about temperature!
Find something else to do and enjoy your travelling.
AnswerID: 597595

Follow Up By: pop2jocem - Monday, Mar 21, 2016 at 11:09

Monday, Mar 21, 2016 at 11:09
Agree completely shane. Life's too short to drive around wondering what degrees Kelvin or absolute pressure my tyres are at. I'm sure the guys who pumped up the tyres (tires?) for the moon buggy had to take that into consideration. I feel it is most unlikely I will be travelling in conditions anything like that. LOL.
Whether you use internal or external sensors depends IMHO on whether you do mainly bitumen driving or a heap of off road stuff that may damage rims or the sensors themselves.
Personally I would use the external type but that's just me. All I need to know is that a tyre is loosing pressure so that I can stop before too much damage may make the tyre beyond further use or cause a much more serious accident from loss of control of my rig.

Cheers
Pop
1
FollowupID: 866659

Follow Up By: TomH - Monday, Mar 21, 2016 at 13:32

Monday, Mar 21, 2016 at 13:32
Ha ha The Moon buggy (Lunar Rover ) had metal tyres that didnt pump up LOL

The wheels consisted of a spun aluminum hub and an 81.8 cm diameter, 23 cm wide tire made of zinc coated woven 0.083 cm diameter steel strands attached to the rim and discs of formed aluminum. Titanium chevrons covered 50% of the contact area to provide traction. Inside the tire was a 64.8 cm diameter bump stop frame to protect the hub.

Saw one at Cape Kennedy that had rubber tyres and was a prototype used on earth.

Had moonbeams to inflate the tires.
1
FollowupID: 866667

Follow Up By: Allan B (Member, SunCoast) - Monday, Mar 21, 2016 at 13:54

Monday, Mar 21, 2016 at 13:54
But did they have temperature monitors on them Major Tom? lol
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

1
FollowupID: 866669

Follow Up By: TomH - Monday, Mar 21, 2016 at 16:12

Monday, Mar 21, 2016 at 16:12
Specs didnt say but apparently its cold up there and they didnt go very fast.
1
FollowupID: 866676

Reply By: Idler Chris - Monday, Mar 21, 2016 at 11:17

Monday, Mar 21, 2016 at 11:17
This is what I have done for the last 9 years and it has been great insurance, peace of mind and more than paid for itself in saved tyres, and getting good mileage.
I have 6 strap on Sensatyre monitors, one for each wheel. They are strapped on so the monitor is near the valve hole. I have never had one damaged when changing tyres. The cabin monitor shows the 6 tyres constantly and gives accurate readings within a few seconds of the ignition being turned on.
With usage you learn what is the "normal" temperature for given pressures, speed and vehicle load for your vehicle. The biggest killer of tyres is heat and so I endevour to keep the temperature under 60 degrees. To lower the temperature you either slow down or increase tyre pressure or both. The 60 degrees is a target not a critical figure. If I am in a hurry and it goes to 80 degrees it just means that I am not doing the tyre any good but that is the price for going faster. When its 40 degrees ambient and on bitumen which can be 70 degrees plus it is very hard to keep it under 60 degrees so you either wear it or pull over and camp early. As an example for a Toyota 100 series travelling at 90 kph, ambient of say 30 degrees, and loaded to near GVM I would have the fronts at 55 PSI and backs at 65 PSI. This will give you a slightly harsher ride but it is better for your tyres, its your choice. I have always been happy with the mileage I have had from my tyres and I believe my management of the heat in the tyres is a major factor in achieving good mileage.
The tyre sensor is monitoring tempreture. This is a combination of the air inside the rim and the rim itself. The rim temperature will rise should you have a faulty wheel bearing, dragging brakes, or possibly some other factor. As I said above you will learn what is "normal" and any increase from normal indicates a problem which needs to be investigated and corrected. So your tyre monitors are monitoring more than just your tyres.
I see no difference between knowing your wheel temperatures, engine temperature and transmission temperatures, its not the absolute value, but any change from "normal" that is a good indicator of a potential problem. If you are like me, a serious outback traveller, a reliable vehicle is paramount, and any aids that can indicate a possible problem could potentially save your life.
In relation to cost, mine have paid for themselves in the tyres that they have saved. Even if they had not saved even one tyre I would still have them because I travel many gravel roads, most have plenty of bends in them, and I do not want to EVER be travelling on a partially deflated tyre. My life is worth far more to me than the cost of good reliable tyre monitors.
You can agree or disagree, this is what works for me and it gives me great peace of mind that I have done everything thats reasonable to ensure the safety of myself and passengers.
What other people think of me is none of my business.
Do unto others what you would have them do unto you.

Lifetime Member
My Profile  My Blog  My Position  Send Message

AnswerID: 597598

Follow Up By: Allan B (Member, SunCoast) - Monday, Mar 21, 2016 at 13:50

Monday, Mar 21, 2016 at 13:50
.
Hi Chris. I agree with all you said.
I too aim for no more than 60 degrees and get nervous if they go over 65.
My current tyres are rated at 80psi max so I am unlikely to get close to that, but when running at dune pressures and 40c ambient I could easily push the temperature up to unacceptable temperatures so I do like to monitor that parameter.
I just wish that I could determine what the manufacturers consider to be a maximum temperature. Even so, any elevated temperature is going to have a deleterious effect on the strength and life of the tyre composition so keeping it below 60 degrees seems to be good practice in my mind.

Your comment re the sensors reacting to bearing or brake temperature is interesting and not previously considered by me. Certainly I can see that possibility even though the correlation might be 'sloppy'. But, as you say, the deviation from 'normal' would be an indication and be particularly highlighted as being from just one wheel departing from the others. It was a good point of yours.

You say, "my life is worth more...." But some may consider that monitoring the beer fridge temperature is more important! lol
Cheers
Allan

Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 866668

Follow Up By: Echucan Bob - Tuesday, Mar 22, 2016 at 05:30

Tuesday, Mar 22, 2016 at 05:30
Chris, I agree with your tyre monitoring philosophy. The only point I'd make is that when it comes to temperature, sudden changes and isolated changes in one wheel relative to the others are important indicators that all is not well. These are more important than absolute values.

The temperature of a tyre is determined by ambient road and air temperature, the evaporative cooling effect of water on the road, direct heating by sunlight, conductive heating from brakes and bearings and, most importantly, heat generated internally from the speed of rotation and amount of side wall bagging (the bulge in the side wall near the point of contact with the road). The amount of bagging is determined by load and pressure, but varies when the tyre acts as a shock absorber on corrugations.

The change in temperature of a tyre is as important an indicator of imminent trouble as a change in pressure, such as when there is a slow loss of air due to a puncture. Both are important, and ignoring temperature monitoring is just silly.

Bob
1
FollowupID: 866692

Follow Up By: Idler Chris - Tuesday, Mar 22, 2016 at 07:44

Tuesday, Mar 22, 2016 at 07:44
Hi Bob, I thought that's what I said. However you have made it much clearer and what you have said is totally correct. The external monitors only do half the job because the temperatures they show are not accurate enough. I see knowing any sudden or unusual change of any of your tyre/wheel temperatures a safety issue and therefore their cost a necessity. Chris
What other people think of me is none of my business.
Do unto others what you would have them do unto you.

Lifetime Member
My Profile  My Blog  My Position  Send Message

0
FollowupID: 866695

Reply By: The Bantam - Saturday, Mar 26, 2016 at 12:45

Saturday, Mar 26, 2016 at 12:45
A few thaughts.
People get all sorts of ideas about accuracy and tyres ...... truly there are so many variables .... so many inherant inaccuracies.

As for rules of thumb ...... oh hell see " so many variables" ......

The 2 psi/4psi/6psi whatever rule ...... it is so unrelable as to not be a rule at all .... I tested it on one of my vehicles and got bugger all pressure increase even with tyre way below and way above Load V pressure tables.

There truly is only one thing that can be relied upon ..... "cold inflation pressure"

And that derived from load V pressure tables for that specific tyre size and profile.

ALL your tyre pressure decissions should be bassed on the measured weight per axle and use of "minimum cold inflation, load V pressure tables" for the tyre in use.

Unless you have weighed your vehicle loaded, measuring each axle or axle group and consulted Load V pressure tables ........ sorry but frankly you have no idea what tyre pressure you should be running.

A few PSI increase for highway work or hot weather is very reasonable.

IF you deflate for off road purposes .... those deflated pressures should be bassed on the cold inflation pressures indicated by the load V pressure tables.

DO NOT rely on what people in tyre shops tell you.


One thing that must be understood is that If the tyre is close to optimum pressure, the temperature and pressure will tend to self regulate ..... as the temperature of the tyre increases, so will the pressure within the tyre and things should tend to equalise ......... If anybody tells you they have a formular or some sort of rule of thumb .....They are kidding themselves....... see so many variations.

As for accuracy of tyre pressure measuring equipment ..... Oh hell don't get me started ....... A few years ago I went looking for a new tyre guage ........ I won't go into detail ...... but just finding a simple tyre guage at any price that is close to accurate and consistent and remains so over time is a mission in its self.

In particular I found many of the digital/electronic guages that start off very accurate don't stay that way long ...... it is a good piece of electronics that remains accurate and reliable under constant pressure, heat, vibration and time. ...... consider that when buying.

As for brakes and rim temperatures ..... Back when I was in the rallying sceene .... I sat in the forrest many nights and saw car after car comming thru my controlls with orange disks and a dull glow come from the rear drums ..... and seen service crew either burn their hands unaware or wear gloves to handle wheels when changing tyres.

Brake temps will change rim temps ..... if your guage senders are fixed to the rim ... it is an issue.


These remote tyre monitoring devices are a great idea ....... but don't get all bent up about variations in temperature and pressure for normal, properly inflated healthy tyres.

What you should realy worry about are drastic, changes in a single tyre.

cheers





AnswerID: 597799

Follow Up By: Member - johntoyo - Saturday, Mar 26, 2016 at 13:36

Saturday, Mar 26, 2016 at 13:36
Thanks Bantam.
I fully realise gauges and such things as TPM's sytems have inherent inaccuracies. I just want and got an idea what to set my upper limits (to expect) for pressue and tempreture.

Will adjust based up what I see.

Thanks to all contributors for your views and inputs.
0
FollowupID: 866832

Follow Up By: The Bantam - Sunday, Mar 27, 2016 at 00:21

Sunday, Mar 27, 2016 at 00:21
Here is a couple of other things to think about ...... most light truck tyres we see on utes and 4wds have the maximum load capacity at a minimum cold inflation pressure of around 60psi though some its up around 80psi ..... again load V pressure tables specific to your tyres will be most informative

It would be reasonable to cold inflate as much 5 to 6 psi over for highway use ...... so a hot tyre pressure of the order of 70 - 75 would not be surprising. on a maxed out rig. or even 90 if high load range tyres are used.

60C will cook meat and scald flesh ..... while I have never see a functioning tyre too hot to touch ..... I have seen rims so hot they sizzle when spat upon, due to brake heating.

I'd be most concerned with rapid pressure loss than anything else.

cheers
0
FollowupID: 866847

Sponsored Links

Popular Products (13)