Looking for a little advice. Ive recently fitted a tyre pressure monitoring system all is good and quite impressed but it is showing the n/s/f unit tyre as up to 160psi when running.
Tyres are 120psi cold, temps are fine (40-50 when hot)
o/s/f maxes at about 140.
150+ seams very high but all seems fine
Any advice or ideas
Thanks in advance
The sender units are simply screwed onto the valves?
Swop front left and right over. That should tell you whether the tyres are actually different pressures or whether the senders are inaccurate.
Tried that 1 - no difference at all.
Wondering if its a problem with the tyre, the truck or just normal. Loads online about min tyre pressure but nothing about max or running pressure. Tyre sidewall only gives max pressure cold (130)
Swop front wheels side to side? That’ll show if it’s position or tyre,
It’s just more electronics to go wrong, just bin it, and go back to the old ways, eyeballs and a manual gauge.
Franglais:
Swop front wheels side to side? That’ll show if it’s position or tyre,
Thats the next move - i know that the o/s/f will always have a higher pressure due to the camber of our roads, and while i have a few options to check its more an answer of what is the expected running pressure that im after.
As for electrics to go wrong - they haven’t! They are spot on - checked with analog and digital
Going back to C&G about 50 years ago, the theory goes that if the load carried by the offending tyre is greater than on its partner on the opposite side of the axle then the volume of air in the tyre decreases slightly because the carcass is squashed. As the volume of a gas decreases the pressure increases. As the vehicle goes along the temperature of the air inside the tyre increases this also results in an increase in pressure.
In practice it is just as likely that there is a difference in the physical composition of the two tyres if they are not identical. You could try swapping wheels and sensors around or checking pressures hot and cold with the axle jacked up. I assume that all pressure monitoring devices are calibrated? It is also common to find that Schrader valve cores do not always act smoothly when taking pressure readings.
Put a good old manual gauge on them 1st thing when cold ,note readings ,compare to computer reading ,if they read the same .ok …Then do the same at your first break and again compare and take it from there…A lot of things can influence the pressure ,a brake for example
Are the tyres all the same make and roughly the same age ■■?
norb:
Put a good old manual gauge on them 1st thing when cold ,note readings ,compare to computer reading ,if they read the same .ok …Then do the same at your first break and again compare and take it from there…A lot of things can influence the pressure ,a brake for exampleAre the tyres all the same make and roughly the same age ■■?
They have been checked with a manual and digital gauge all pressures are spot on first thing.
Then after driving they all raise by around 10-15psi which I would consider normal apart from the n/s/f which raises by about 30, up to over 150psi - which has also been checked on an old school gauge.
All tyres are 2 months old, all replaced for test in may.
I understand that the n/s/f may raise higher due to the camber of the UK roads but the queations im looking for the answers to are
Is 150+ to much?
What is an acceptable pressure for a hot truck tyre?
What pressure can you expect the sidewall to blow out?
Ive googled and googled and there doesn’t seem to be a definitive answer to any of em
Why in your first post to you say 150psi seems very high?
What are you comparing that to?
If all pressures were 160psi, when you first fitted these monitors, would you think they were all excessively high?
In the absence of other evidence I wouldn’t be at all concerned.
Franglais:
Why in your first post to you say 150psi seems very high?
What are you comparing that to?
If all pressures were 160psi, when you first fitted these monitors, would you think they were all excessively high?
In the absence of other evidence I wouldn’t be at all concerned.
Is it high though ■■ Thats what im trying to find out
The fact that 7 of 8 tyres increased by about 10% and 1 by over 20% is what concerns me, if they all increased roughly the same i don’t think i would have paid that much attention to it.
The high pressure sensor is factory set to 150 and ive had it up to 163.
If the tyres are safe at say upto 200psi then its not a problem but there doesn’t seem to be an answer out there
If the tyre is good at 130psi cold, it will be safe to take significantly more when hot. A properly inflated tyre will run cooler than an under inflated one, so a higher cold pressure will give you a lower hot pressure.
newmercman:
If the tyre is good at 130psi cold, it will be safe to take significantly more when hot. A properly inflated tyre will run cooler than an under inflated one, so a higher cold pressure will give you a lower hot pressure.
An under-inflated tyre will run hotter.
Gases expand when hotter, or in an enclosed space will be at a greater pressure.
So an under-inflated tyre will automatically get up to a higher pressure and cure any problems without any worries.
Dunno what all the fuss is about?
Yes, I know that`s bllx…
More seriously, would a temperature sensor for tyres not be a better tool? Remote infra-red measuring?
Wed need to know what constitutes a dangerously high temp of course. And as here we havent seen what a dangerously high pressure is.
Knowing the pressure or temperature is only useful if we know what the safe limits are, and yes, that was part of the OP`s enquiry.
Yeah, that’s why I said it would ok, the manufacturers have obviously done the maths on the increase in pressure as temperatures climb, so if it’s good for 130psi at ambient, it will be ok at running temperatures.
As you say, under inflation will sort out the problem with a bang, due to sidewall flex and the resulting heating of the internal structure of the tyre, which gives a much higher temperature and corresponding increase in pressure that overwhelms the tyre.
What that temperature and pressure is must be out there somewhere, the tyre manufacturers have huge R&D budgets, so they’re sure to have found out.
Here’s a gift from me to anyone who has the time [emoji2]
newmercman:
Yeah, that’s why I said it would ok, the manufacturers have obviously done the maths on the increase in pressure as temperatures climb, so if it’s good for 130psi at ambient, it will be ok at running temperatures.As you say, under inflation will sort out the problem with a bang, due to sidewall flex and the resulting heating of the internal structure of the tyre, which gives a much higher temperature and corresponding increase in pressure that overwhelms the tyre.
What that temperature and pressure is must be out there somewhere, the tyre manufacturers have huge R&D budgets, so they’re sure to have found out.
Here’s a gift from me to anyone who has the time [emoji2]
Well I’ve taken up your kind offer of a free search, didn’t find an answer to the OP’s questions, have learned a few things though, or more confirmed my belief about tyre aging, after replacing 3 trailer tyres this week, all had tread left, but were cracking on the side walls and in the grooves, they were all manufactured in either 2012 or 2013, better to replace them at home for £200 each than think you’re saving money by leaving them and have them blow out somewhere in Europe and get them replaced at £500+ each. The fitters also checked and adjusted the pressures FOC of all the other tyres on all our trucks and trailers, which did throw up a few surprises, mostly that they’re not check at PMI’s despite us getting a pressure reading on the sheet.
Is it a 5yr best before date on tyres?
muckles:
Well I’ve taken up your kind offer of a free search, didn’t find an answer to the OP’s questions, have learned a few things though
As did I, and Im sure the OP did too. Maybe a call is in order to a tyre manufacturer? Looks like a nice, easy, clean, pressure monitor is excellent for checking cold pressures. (No need to trust those garages) Dunno about anyone else, but without knowing any data concerning max allowable hot/running pressures Id ignore those readings unless they altered from the apparent “norm”. For me (based on no evidence) 10 or 15psi being less than 10% is ignorable.
Interesting but nothing to worry about.
newmercman:
Is it a 5yr best before date on tyres?
Didn’t actually find an age recommendation but more the effects of aging on tyres,
Generally tyres wear out before failure due to aging occurs. However, for vehicles or trailers that are only used occasionally (e.g. recreational vehicles) aging could be an issue. Since climate and exposure to sunlight affect aging, no date can be given at which a tyre expires. Recommendations for changing tyres range from 4 to 10 years. Aging may be observed by cracks on the tyre surface. However, according to NHTSA, tyres are primarily degrading from the inside-out, due to permeation and reaction of the pressurised oxygen within the tyre structure, with rates proportional totemperature. Cracking can eventually cause the steel belts in the tyre to separate from the rest of the tyre
My experience of race transporters, which do low mileage, so never actually wear out the tread, is around the 5 to 6 year mark the cracking becomes noticeable,
which according to the stuff I’ve just read also means the tyres are less flexible and less able to withstand the deformation cause by hitting objects, not that I bounce them over kerbs, but plenty of other things like road imperfections which the tyres ride over at full speed.
Secondly tyre ageing can be a significant factor due to reduced heat resistance of the tyre, and also the resistance to impact with obstacles is reduced, as explained most clearly on the website of Bridgestone
There are three main mechanisms of tyre ageing. The first involves rubber becoming more brittle. Sulphur is used to link rubber molecules together during vulcanisation with the application of heat and pressure, giving the rubber its useful elastic properties and strength. As the tyre absorbs energy in the form of light, heat or movement the tyre continues to vulcanise. This ongoing vulcanisation causes the rubber to become stiffer and more brittle. The second mechanism of tyre ageing is oxidation involving oxygen and ozone from the air compromising the strength and elasticity of the rubber and the integrity of the rubber to steel bond. Basically heat and oxygen cause cross linking between polymer chains (causing the rubber to harden) and scission of polymer chains (leading to reduced elasticity).Thirdly, breakdown of the rubber to steel-belt bond will occur due to water permeating through a tyre and bonding with the brass plate coating on steel belts. This causes the steel to rubber bond to weaken leading to reduced tyre strength and reduced heat resistance. If compressed air used for inflation is not completely dry, tyre strength will be affected over time. Even unused tyres will become more brittle, weaker and less elastic with exposure to water, air, heat and sunlight.
I believe DVSA have some regs on tyres more than 10 years old, might use another Google free pass to find out. 
Franglais:
muckles:
Well I’ve taken up your kind offer of a free search, didn’t find an answer to the OP’s questions, have learned a few things thoughAs did I, and I
m sure the OP did too. Maybe a call is in order to a tyre manufacturer? Looks like a nice, easy, clean, pressure monitor is excellent for checking cold pressures. (No need to trust those garages) Dunno about anyone else, but without knowing any data concerning max allowable hot/running pressures Id ignore those readings unless they altered from the apparent “norm”. For me (based on no evidence) 10 or 15psi being less than 10% is ignorable.Interesting but nothing to worry about.
I think TPMS are systems are great for warning of impending issues; I have a system on my motorbike and will get a warning if it goes out of acceptable parameters.
We also use them on the racing cars with the data being transmitted to the Engineers data centre in the garage, I still have to check and adjust pressures when the car comes into the pits, but the systems are very accurate and even under normal conditions the pressures on race tyres can rise by nearly 100% from being set cold first thing in the morning to running at full heat on a hot circuit in the middle of the day.
newmercman:
Is it a 5yr best before date on tyres?
5 or so years seems to be recommended as near limits.
If theyre on a vehicle that never moves, exposed to sunlight and the elements, may be different than being stored in a cool dark place. Ill bet the average caravan never gets its tyres worn down to the limit, and wasnt that horse-box/camper thing that had a front blow out and crossed the carriageway on old tyres?
For anyone in doubt, since 2000, the tyre date of manufacture is a four figure code in an oval on the side wall. First two digits are the week, second two the year.