Tyre pressure/temperature monitors

A new term? Forgive me for being a little ignorant but what do you mean by a "dust hole"? I can come up wit a few possibilities.

Phil

That's interesting, I have had the same monitor ( Sidewinder sells the same unit) for 6 years. Great unit. I haven't had any issues with valve stems other than the sender hitting the alloys. That is Cape York and back, ABH, CSH, Simpson, Ooodnadata, Old Ghan etc.

They have saved my tyres on several occasions on the trailer I recon.

So the system worked in that it let you know of the 2 flats that it caused??

Can't wait to get some. lol

Paul

Were the valve stems replaced with new when the tyres were fitted?
In my tyre business it was my policy to install new valve stems when fitting New tyres, some places don't. They should last a tyre life , even with a tyre monitor attached.
Then there has been some inferior valves around too.
Cheers

Shane,

Yes, the first thing the tyre bloke did when the tyre came off each rim was to slice off the back of the old valve core and whack a new one in.

Roachie

I've used TPMS tyre monitors on our Land Cruiser for over 6 years.
Our travels have taken through The Simpson, The Gulf Country, Western Queensland, The Cape, High Country, Western NSW and Corner Country and more.
The first time the system saved a tyre it paid for itself.
We have never had a tyre stem fail. We've never had a dust hole cause a flat either.
I'm not sure what tyres you run but our current set of Toyos have been running over the country for 90,000 kms and we've had two flats - one after an off track trip on a property near Cunnamulla and the other picked up a piece of 19 x 19 dressed timber painted green and white about 100 mm long that staked a tyre on the Sandover Hwy west of Lake Nash. Both times the tyre dogs save the tyre which are both still running on the vehicle.

Steve

Dust hole is a bloody big pot hole filled with dull dust and if you are unlucky enough to drive through one you could just dint your steel rim enough to cause a flat, as when travelling in these areas the tyre pressures are down to allow tyre flex
The van is not quite three years old so valve stems and tyres are same age.
Will be following up with tyre fitters to change valve stems to shorter or solid if possible.

I knew what a bull dust filed hole was. First encountered me before I got mu licence. They are fine provided you are ready for them. Well almost!

I thought it was a new abbreviation or phrase to do with a chunk of dust getting into the bead/ rim area and letting air out. A bit like "veg" instead of vegetables.

Phil

I guess this debate has been had several times on EO Allan. ( like all debates on EO)

Both have their advantages but IMHO the external ones are superior for some applications, like if you have multiple wheel sets and spares. I can see that internal ones are better for normal on road use where tyres and wheels stay put though.

I think External ones are superior because
-I just swap the sensors when changing from my AT wheel set to my MT wheel set.
-Its easy to change the sensors to new rims
-Managing multiple spares is much simpler.
-It's easy to damage internal ones when changing a tyre yourself.

Also temperature is a lagging indicator, and a slow one at that, telling you that your tyres are 'under pressure'. While internal ones are undoubtedly more accurate, the external ones do show increases in temp. But the pressure alarm will have gone off well before tyre temp rises. Many vehicles with OE TMPS don't even monitor temp any more ( BMW)

I don't use either type, but just on Boobook's comment about temperature, at least internal ones will alert you to a dragging brake etc. Not as critical as a sizeable pressure drop, but also something that many drivers don't check for.

I normally do a walkaround feeling the discs through the wheels after a stint on the road. Any DIFFERENCES (side-to-side especially) may indicate bearing issues etc and should be investigated.

From a cold start one morning, I did about 1km to refuel. Did a quick temp check - fingers onto discs. One disc was decidedly warm. In 1km? Turned out to be a dragging handbrake due to mud inside the mechanism. If I spent long enough "out there" I'd probably invest in one of those IR thermo-gauges.

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Well yes Boobook. I didn't really want to fire-up the internal/external debate again but as Roachie was espousing the issue of resolving the valve stem problem I thought to suggest the internal option.
However as you have raised some issues I feel some need to address them.......

Sure, internal have some advantages such as lower price and ease of wheel swapping but I run two spares and have no trouble swapping as each transmitter is paired to a "key" on the receiver which is very easy to re-correlate the wheels. Really no different to "swapping the sensors". That addresses three of your points. I have not found your fourth point of "damaging internal sensors when tyre changing" to be a valid perception. I have not had such difficulty. If you are aware of the presence and location of the internal sensor then applying standard practice to tyre changing will cause no problem whatsoever. Clumsy changing is just as likely to damage the bead or rim as a sensor.

The issue of temperature is far more important than you acknowledge. The selection of lowered tyre pressure based on tyre specification, load and speed is arbitrary. Tyre manufacturers can offer only guidelines, not absolute pressure values and we users adopt our own arbitrary pressures. Observation of pressure rise from the arbitrary starting pressure then gives an indication of tyre temperature rise but without dimensional relationship to actual temperature. The monitor indication of this temperature is really quite responsive, not as lagging as you suggest, and a very good measure to avoid reaching harmful tyre temperatures. I do not suggest that it is of any value as an alarm of overly low pressure...... the pressure monitor and alarm looks after that quite well.
What the temperature indication does do is to reveal that you are operating within the safe pressure/load/speed envelope. I use mine to keep a close watch on this upper temperature value whenever running with reduced tyre pressure, particularly during the first 15 minutes or so of reducing the pressure. Observing the pressure rise is also an indication of temperature rise but it is dimensionless and cannot be directly related to tyre safety specifications.

When it comes right down to it, what damages a reduced pressured tyre is not the low pressure but the temperature created by the flexing of the tyre. Monitoring pressure for that criterion is purely inferential when it is the real temperature that is crucial.

Finally, I would suggest that external sensors are hopeless as providing any real correlation of actual tyre temperature other than "it has gone up a bit". They are well removed from the target and considerably influenced by environmental factors. My many years in Process Measurement and Control have taught me that accurate temperature measurement is probably the most difficult of all basic measurements with pressure being the easiest.

Sorry if this became a lengthy articulation but I consider it worthy.

I carved some ugly fat collars out of a lump of stiff closed-cell foam. These sit between the valve stem and the rim and
a) stop the sensors bashing themselves to death in corries, and
b) on alloy rims, stop the sensors marking them



The contact marks you can see are old wear from before I made the collars.

I like Roachie's idea much better.

(I really must get around to re-finishing the wheels :-( )

Cheers

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We also have Sunrasia rims Phil with internal sensors.
Why your aversion to internals? They really do cover all bases and never a moment's trouble.

Just don't like the idea, Allan. How long would the battery last. What if one comes loose. What if one breaks, not easy to fix. I also have two sets of rims, one for light sand and one for the high country etc. That's ten rims. While cost is an issue it is still part of the choice.

Phil

Fair enough Phil.

Phil,

Not sure I understand this...QUOTE: " I also don't want to drill any new holes as it's bad enough getting to these ones in the snow as is." UNQUOTE

The whole idea of drilling the new holes and mounting the sensors the way I have is so I never have to get to them again. They are on and I can forget about them now.....until the battery goes flat, but even then changing the battery can be done with them in situ.

I do also like the idea of the internal style, which is what I have on the truck. I just didn't know if the Safe-T-Tyre brand uses the same frequency that they make internal sensors. If I start to experience issues with these external sensors (breaking etc) then my next investigation will be into finding out what the frequency is and seeing if I can get internal ones the same.

Roachie

If I don't drill new holes then I have to take them off to alter the tyre pressures. It's bad enough getting to the valve stems to remove the caps as is let alone with sensors on. "Harder" still in snow. I don't know about yours mate but mine seem to get clumsy, stiff and bigger when in the snow.

Phil

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It is difficult to obtain definitive data on tyre temperature recommendations. Tyre manufacturers generally do not publish this information yet I would believe that they have such information available. When they do rate tyres for temperature they do so by assigning letters of classification...... 'A', 'B' or 'C' with 'A' being the higher classification. This grading is derived by destructive testing with increasing speed under load. It is a tyre selection guide only and not very helpful in vehicle operation. I have found tyre industry references to 80C being an upper safe limit but cannot locate that reference at the moment. It is possible that the industry has not publicised definitive temperature information because until the advent of TPMS systems the user had no way to utilise such information.

Some more detailed information on tyre temperatures can be found on sites related to the motor racing industry. This may not be directly related to 4WD touring but does seem to point to 80C being an upper limit. They of course have interest in temperature for reasons of rubber traction.

There can be no doubt that increasing temperature has a deleterious effect on the strength of rubber tyres just as it has on all physical solids. It is the excessive temperature that weakens the tyre allowing the physical operating forces of sidewall flexing to create destruction stress and ultimate failure even when the tyre air pressure is well below the manufacturer's declared upper limit.

Those TPMS systems that incorporate high temperature alarms seem to select 80C as the nominated alarm point. When necessary, I keep a watch on my tyre temperatures and become concerned should they exceed 70C and take action to reduce any further rise by either lowering speed or raising tyre pressure. I have needed to do this twice in my travels, each time by lowering speed. Knocking off a couple of k/h made a significant temperature reduction.

My TPMS comes with a default max temp of 70 C.

The tyres have never got within cooee of that.

Internal or external sensors Sigmund?

External Allan. From ABR Sidewinder.

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Well Sigmund, "external sensors"...... there is the reason why your tyres have "never got within cooee of that."

The almost last paragraph of my Followup ID: 873189 above said..... "Finally, I would suggest that external sensors are hopeless at providing any real correlation of actual tyre temperature other than "it has gone up a bit". They are well removed from the target and considerably influenced by environmental factors."

Because the external sensor is well removed from the target temperature of tyre carcase and furthermore is actually located in the air slipstream. it is likely to read much closer to the air ambient than the tyre temperature. The external sensor will read the pressure OK as it is directly connected to the air within the tyre carcase but it will not even come close to the temperature of an operational tyre. For TPMS manufacturers to include the temperature feature in an external sensor is inappropriate and misleads users.

I'll pass on your opinion to Derek Bester of ABR Sidewinder. He'll be interested to hear he's been selling something that can't work in respect of temperature.

And how would you explain why 3 tyres consistently read similar temps while the 4th is above those?

I'm with Allan B on this. Simple physics says external monitors out in the slipstream cannot possibly measure the temperature of the tyre, be it internal air temperature or carcass temperature.

As to the variation between units, you get that with pressures, even when a digital gauge says all tyres are the same.

I don't believe that pressures the external sensors report - the varation is too great in my experience. Instead I rely on them purely to report a slow deflation, which is where a tyre will get wrecked when it could be saved if you know about it.

Cheers

I would be quite happy to debate the technicalities of temperature measurement with Derek as it is my profession, but it is not he who is manufacturing the device, merely selling them. Actually, I doubt that Derek will be at all interested!

As to your question re 4th tyre inconsistency........ there could be a number of reasons, the most likely being calibration error of that sensor, but only testing of the sensors could establish the differing readings. In this science we do not jump to conclusions but examine the device scientifically to determine accuracy.

Maybe it works by conduction.

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Sigmund, you can "maybe" all you want, but it will not match my lifetime working in the field of process measurement, including temperature.

And you've tested the product Derek sells?

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Oh come on!!!! I'm not the one proclaiming that one sensor is reading significantly high. You can explain it or you can send them to me for testing. Until then I have no further interest in your uninformed expressions.

You invoke the standards of science and then use an ad hominem argument in support of your key assertion. Hah.

Allan your posts have sparked my interest in what is too hot. It seems like there is almost zero information about what is a reasonable limit. Not even the classification you refer to gives any hint of temperature limits. Nearly every webpage on the matter mentions pressure leading to over temp, but don;t quantify it.

The only reference I could find was a US Michelin document that said that tyres start to break down over time at 160 degrees F. That's about 70 C.

It seems that is the only reference that gives any recommendation that I can find. It appears the more you are over that temperature, the quicker the degradation. TMS settings aren't much help either, there are lots of TPMS that I looked at. (I only looked at internal ones), some are set to 80, some to 70, some 90 and some don't give a default in the manual. About half seem to have a configurable value.

Every document I could find said that over temperature was caused by under pressure, so while my external unit does not accurately record temp, I still believe it doesn't matter, especially since no one knows what the limit is. 70c, 80c, 90c for 20 minutes?

I am surprised that there is almost zero info out there. Have you found any definitive information on how hot is too hot for tyres? Maybe that is why some OE systems like BMW don't even monitor temperature.

I monitor my bearings and shockers with a IR thremometer, I might compare the IR reading with the TPMS reading for a while. Not that I currently know what is too hot.

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Boobook, I also searched for temperature info on the tyre manufacturer's sites and found only a couple which I cannot now locate but remembered them as 80c or thereabouts.

Yes, reference is usually made to low pressure being the cause of tyre failure but that is probably because internal sensors providing reasonable determination of carcase temperature have only been available in recent times. Certainly low pressure is the major contributor but so also is speed and load. It is the combination of all three that determine the sidewall flexing and thus temperature rise and tyre destruction.

I understand that most OEM monitoring systems (such as BMW) do not actually measure pressure (and certainly not temperature) as they infer low pressure in a tyre by measuring the rotation of the tyres as a comparison to the remaining tyres by using the data obtained by the traction control system. Not actually pressure measurement at all but low cost to obtain.

Good idea to observe your tyre temps using your IR thermometer.
What I intend to do at the first opportunity is refit my original Tyre Dog externals and log comparison temperature figures with my internal system. Should be interesting. Mind you, we still do not have industry data.

Allan, comparing internal to external would indeed be an interesting comparison. My money is on external ones taking 10 - 15 minutes longer to register a temperature rise, and only measure about 70% of the difference between the tyre temp and ambient. Though i did find on one website that brass stems make the error quite small. That adds weight to what the OP did.

I am pretty sure BMW for example do measure pressure. My wife has one with runflats and had a slow leak. I could pump the tyres up, reset the system and it would alarm in the morning again.

Also the rolling radius of a flat tyre is the same as an inflated tyre believe it or not. A flat tyre on one side will turn at the same number of rotations as the other side.

Doesn't sound right but it is when you think about it.

Things are never as simple as you first thing huh?

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Boobook, I am not convinced that a flat tyre has the same rolling radius as an inflated tyre. Still trying to get my head around that.
However, there is no doubt that car manufacturers are using the ABS system to detect low tyre pressures. To that end I offer several references.........

1) Tyre Review

2) Toyota

3) Schrader

4) Volkswagen

5) And even some BMW

There are many more references of course, just Google "ABS tyre pressure monitoring".
The indirect method is of course inferior to the direct method.

The USA Dept. of Transport has required all new light vehicles to be fitted with a TPMS system since 2005. It does not specify that the system must be direct method.

Yes I agree the references do indicate the speed sensors are used.

However look at this. It is pretty dammed close inflated and deflated. About as close as new / old tread on similar tyres.\

I have no idea how an ABS sensor coudl pick up that small difference and the tyre is fairly flat compared to what my wife's was.

???

Yes Boobook, I have seen that video.
I understand that for the 'indirect ABS' system to work the tyre has to be below 20% inflation. Not sure that the tyre in that video is below 20%. Also, as I think some longitudinal compression of the tread occurs in order to create an effectively reduced circumference, some speed may need to be present and the video has no effective speed component.
Whatever, American car manufacturers appear to employ the 'indirect' method in order to satisfy the US Dept of transport. But I'm not too sure how it would stand up to a heavy duty 4WD tyre bouncing along the AB Hwy corrugations.

This is Derek Bester's summary of his system:

1. Temp registered is not 100% accurate due to ambient temps.
2. When left to sit for a while it gets close as the temp gets into the sensors.
3. The rolling figure remains useful as an indicator of binding brakes or failing bearings.

Derek's reply was same-day so he is in fact interested in the issue.

The bloke in the webpage link below has a very well written article on TPMS's (it starts about 2/3rds the way down the very long page.

He goes through all the different varieties of TPMS's, their advantages and disadvantages, and also outlines the improvements in TPMS technology coming.

It appears most TPMS's have drawbacks of some kind. The ones mounted to the drop centre of the rim are apparently the more accurate, but still have the disadvantage of inaccessibility, and battery life.

It's interesting to note what he says about how long these style of TPMS's could have been sitting on the shelf, before you purchase and install them, thus making for a short service life.

He also notes the figure of 80 deg C/176 deg F as being the number that tyre manufacturers state as the recommended "do not exceed" tyre temperature.

Tyre Bible

Cheers, Ron.

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Ron,

I have been aware of the "Wheel & Tyre Bible" webpage for some time. It certainly is a comprehensive review of TPMS but errs a little here and there.

His concern about 'battery shelf life' is not entirely justified. These sensors 'power-down' when not in motion so their batteries are not being consumed whilst on the shelf, or when the vehicle is not in use for that matter. The type of batteries employed have very long life when at rest so 'shelf-time' is not a significant factor. It is interesting how authors can focus on inconsequential and conceptual factors when they are looking to bloat their article.

You say that "The ones mounted to the drop centre of the rim are apparently the more accurate". I cannot find such reference in the subject article. In point of fact, there is no reason, other than manufacturer differences, why there should be any difference in device accuracy between a) Internal well, b) Internal valve stem mounted. or c) External valve stem mounted. The device is essentially identical, merely differing only in packaging and location.

You further say that "The ones mounted to the drop centre of the rim..... have the disadvantage of inaccessibility, and battery life." I see the 'inaccessibility' as being an advantage in protection from physical damage, and battery life is not such a 'big deal'. Mine have been in place for almost 6 years through two sets of tyres. I am soon due for tyre replacement and will replace the sensors at that time..... maybe replace even the entire system. It's price is not large in relation to two (x6) sets of tyres that it protects.

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Ron,
"Hand-on-the-Vessel" was the technique often employed by process operators before my profession came along and installed instrumentation.
One fellow used to place his hand on the vessel and 'count elephants'...... "one elephant. two elephants, three..." etc. until he had to pull his hand off. He had some scale to relate to temperature. Don't know what animal he used when we metricated. lol

And I would generally agree with the operational temperatures you have nominated for car tyres.

Allan - Well, I guess that animal would have been a metric elephant, that was 10% smaller, of course! LOL

I haven't seen anyone mention that rubber is a very poor conductor - of heat as well as electricity.

As a result, you can have wide variations in temperatures throughout the one tyre.

I've been reliably informed the air inside a tyre can be very much hotter than the tyre itself - which makes sense when you consider the poor conductiveness of rubber.

There's a U.S. company called Longacre who make tyre (tire) pyrometers.
These pyrometers use a small probe inserted by hand into the tyre tread - at various places.

Longacre are racing equipment specialists, and it's interesting to read their instructions for their tyre pyrometers.

They insist on taking measurements at an even depth, and in several places on the tyre, to get an accurate temperature reading.

Cheers, Ron.

Ron,
I would take issue with the air "being hotter than the tyre". The air becomes heated by being in contact with the tyre itself therefore cannot be hotter than the tyre.
I would expect the air to be in fact somewhat cooler than the tyre as some heat will be constantly dissipated from the air to the metal rim and thence to the outside atmosphere.
That is one of the difficulties in making accurate temperature measurement...... ensuring that the point of measurement has not decreased by losses to a cooler zone. (or increased in the case of sub-ambient temperatures) It is the most common error and can be difficult to eliminate.

Despite the thermal losses affecting the air temperature, I would expect the air temperature to be within about -10% of the temperature of the tyre average surface temperature, which is a reasonable representation.

Longacre's interest in tyre tread temperature is of course for racing purposes where the grip of the tyre on the track is the matter of interest. They are not running under-inflated tyres where excessive sidewall flexing is generating tyre heat.

Interesting points, Allan. However, there is another factor involved - the heat being transferred from the brakes to the rim adds another area of heat buildup, that is independent of the heat buildup from the tyre.

If you're driving in hilly areas and braking more than usual, or doing a lot of stop-start driving, where the brakes are getting a workout, then the heat input to the rim is rising substantially over just regular, steady-speed, long-distance driving, where the brakes are rarely being touched.

Naturally, race cars suffer the most, from brake heat transfer to the rim, so they are the extreme example.

Cheers, Ron.

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Hilly driving and constant braking do not usually accompany the circumstances where you would be using lowered pressures and be concerned with high tyre temperature.

If you look hard enough Ron you can find all sorts of influences affecting the precision of a given measurement. The importance is to not let minor effects dominate the worth of the process.
OR, as my mother would have said, "Don't throw the baby out with the bathwater".

Now you have my total attention. "fobo t-valves $21 each and for me $20 to fit to each wheel, $210 all up as I have six wheels"

Where can I get some in Oz?

I would start with six for the desert/home set and later another 4 for the high country tyre set.

Phil

I found some on eBay. Thanks

Phil

you can get them from fobotyre.com.au, yes I think they are on ebay as well, but from memory I got them slightly cheaper direct.

I was a bit quick. Birthday in a few days. I will let the kids worry about it but would prefer Paypal (through ebay) as Paypal provides just one more level of protection.

I may check their site out for a monitoring set though. I want something that will actalluy bolt or screw into place in the dash of one of the overhead console fold down pockets. The Fobo in car monitor is just stuck with double sided tape to something and we aren't too keen on things just stuck on.

Thanks

Phil

Hi Phil, I'm not sure if something may have been lost in translation, as I'm not recommending fobo sensors or monitor, as I've never used them.

I'm recommending fobo t-valves in conjunction with safe-t-dave sensors and monitor (as pictured)

safe-t-dave monitors dont have to be mounted at all, you don't have to look at or see them once set-up, As long as its in the cab it sends an audiable alert when pressure or temp settings fall out of paramenters.

The other advantage of not mounting monitor is you can have it with you at the tire when setting it up, changing wheels or changing parameters, much easier than a mounted monitor.

Hope that clarifies things, cheers Ken

I really miss face to face comms!!! No confusion. I have all the details that I want. All good mate. Note the smile on my face as I am happy with what you said.

FYI; I like a tidy and secure cabin and don't like things loose or just stuck to the dash or windscreen. I don't need it at the tyre. I am happy with the tyre gauge for that. Not a bad hint though for some.

Thanks

Phil

That's a mongrel mate!!! What brand is your system? Warranty claim?

Good luck,

Roachie

Jeez, that's really disappointing to read mate!!

Maybe I should buy myself some spare sensors to carry.