Tyre pressure vs Temperature

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

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

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)

Just a thought, it's interesting to realise we still resist metric when it comes to tyre pressure, staying with PSI readings.

.
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.

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

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.

As per my earlier reply, you don't need to stress about temperature!
Find something else to do and enjoy your travelling.

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.

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