Tyre Pressure warnings....danger of crying wolf too often

[peteo48]

Given the extreme care I have gone to in order to have the pressures dead right, if it goes off again the system must be faulty?

Whilst I don't doubt that you have been as careful as you reasonably can be, the fact remains that you are (probably) using a pressure gauge of unknown accuracy. Others have been dismissive of my idea that gauge accuracy might be a factor, but I have yet to see a convincing argument to demonstrate that any individual pressure reading might not be anywhere within the accuracy band of the gauge, and hence that there might be minor undetected differences between wheels.

My thinking is this. The gauge I used is a new one on a Michelin foot pump. They say it is guaranteed to + or - 1 psi per tyre. It will, presumably, give the same reading, even if slightly inaccurate, per tyre. In short if I inflate the tyre to 33 psi and then inflate the other tyre to 33 psi using the same gauge and pump, then both tyres will be at the same pressure. I struggle with the idea that it will be more inaccurate on one tyre than the other.

Now what seems to be happening is the system, after recalibration, is quite happy for 200 miles or so and then activates randomly. Although I have been extra careful this time, even the last time the tyres were all pretty much even in pressure. Nothing had changed since the calibration 200 miles previously.

Which is why Jocko is right. If it continues to do this, or if it is so sensitive it will fire off if, say, a piece of grit lodges in one tyre and not another, then it absolutely is not fit for purpose. It becomes worse than useless in that you will be tempted to regard any alarm as a false one.

If it goes off again, my conclusion will be that the system is faulty (unless I actually do get a puncture!)

[Jocko]

Found this:
https://www.tpmscentre.co.uk/pages/general-information

First section states:
"TPMS stands for Tyre Pressure Monitoring System, a safety feature that continually monitors a vehicles' tyres and alerts the driver to changes in tyre pressure. The changes in tyre pressure can be detected by either Direct or Indirect means but both methods will, as a minimum, illuminate a warning light on the vehicle dashboard display and sound an audible alert when 25% deflation has occurred."
(Bold italics are mine.)

[Jocko]

Every site I visit quotes 25%.

https://www.tireindustry.org/tire-pressure-monitoring-system
http://www.moderntiredealer.com/article/312219/the-real-benefit-of-tpms
https://www.schradersensors.com/en/driver-education/what-do-when-your-tpms-light-turns

And more.

[Hobo]

Put two new rear tyres on my Civic a week ago, fitter checked that all four tyres were the same pressure, within 5 minutes of leaving the deflation warning came on which I expected, initialised the calibration and drove for over half an hour malnly on rural roads just prior to where we were going the warning came on again, initialised it again and since then no further warnings.

The only other time it had come on was when I left the dealers when we bought the vehicle which I assumed was because they had adjusted the pressures, it also then took two attempts at intialising before it remained off.

[andruec]

I suspect a fault. I check my pressures every couple of months and top them up every other time. In over two years of ownership I've only had the alarm go of twice and both times it was legitimate (one time I forgot to reset it, the other time a pothole on the A34 triggered it).

[Downsizer]

Put two new rear tyres on my Civic a week ago, fitter checked that all four tyres were the same pressure, within 5 minutes of leaving the deflation warning came on which I expected, initialised the calibration and drove for over half an hour malnly on rural roads just prior to where we were going the warning came on again, initialised it again and since then no further warnings.

The only other time it had come on was when I left the dealers when we bought the vehicle which I assumed was because they had adjusted the pressures, it also then took two attempts at intialising before it remained off.

This is consistent with the idea that newly-fitted tyres take a while to settle down, triggering the alarm as they do so.

[guest4871]

Every site I visit quotes 25%.

https://www.tireindustry.org/tire-pressure-monitoring-system
http://www.moderntiredealer.com/article/312219/the-real-benefit-of-tpms
https://www.schradersensors.com/en/driver-education/what-do-when-your-tpms-light-turns

And more.

Interesting. The UNECE site (dated 2010) says (Para 5.3.1) says 20%. Even so, whether is  20% or 25%, it is quite a lot on a tyre pressure of 30 psi (ie 6 psi or 7.5psi). I wouldn't argue the figures except to say that is a noticeably large amount of pressure loss.

https://www.unece.org/fileadmin/DAM/trans/main/wp29/wp29regs/r064r1e.pdf

There was quite a bit of discussion in UNECE about what to use. Less than 20% would risk more false reports with the risk that users would begin to ignore the warning. More than 25% rather negates the idea.

The attached report in 2016 from European Federation for Transport and Environment AISBL is limited but relevant to the topic and  perturbing!

https://www.transportenvironment.org/publications/failure-indirect-tyre-pressure-monitoring-systems-puts-drivers-and-road-users-risk

Quality pressure gauges are calibrated and supplied with a Calibration Certificate by the manufacturer. It is the gauge that is calibrated for accuracy against a standard not it's ability to vary from one reading to another.

https://www.pclairtechnology.com/products/tyre-care-equipment/tyre-pressure-gauges/tyre-safety-pack/

[peteo48]

I suspect a fault. I check my pressures every couple of months and top them up every other time. In over two years of ownership I've only had the alarm go of twice and both times it was legitimate (one time I forgot to reset it, the other time a pothole on the A34 triggered it).

I'm definitely of that mind myself. If it goes off again and there is nothing wrong with the tyre pressures, it must be faulty, there is no other reasonable explanation. The information about the trigger points (thanks Jocko) is crucial here.

[culzean]

It seems to me that the more gadgets that get fitted to cars the less attention people pay to everything.  I am waiting for the Alexa app that will blow your tyres up for you "Alexa check my car tyres and blow them up, Oh and check the tread depth as well because I am too lazy to look" .  I still look at tyres and give sidewalls a quick press on our drive before every journey, and if car has been parked anywhere for a while I will eyeball every tyre before getting into car.   

[Downsizer]

I still look at tyres and give sidewalls a quick press on our drive before every journey, and if car has been parked anywhere for a while I will eyeball every tyre before getting into car.

I hope that airline pilots do much the same!

[andruec]

It seems to me that the more gadgets that get fitted to cars the less attention people pay to everything.  I am waiting for the Alexa app that will blow your tyres up for you "Alexa check my car tyres and blow them up, Oh and check the tread depth as well because I am too lazy to look" .  I still look at tyres and give sidewalls a quick press on our drive before every journey, and if car has been parked anywhere for a while I will eyeball every tyre before getting into car.

The sad fact is that most people hardly ever inspect their tyres. I'd even suggest that the vast majority rely on their MoT or service to point out issues. So that's once, maybe twice a year they get checked. There is a clear need for an automated system that can monitor tyre condition.

Given enough interest and for a price such a system ought to be easy to implement. Proper tyre pressure measurement by the vehicle and led/laser scanning of the tyre surface (side walls included) is technically possible.

As long as the system is reliable I think it could be a major safety feature. Checking tyres manually is like changing gear. It's something a computer could do to save us the bother.

[peteo48]

I agree with andruec on this one. Ideally you want to be able to access the pressure in each tyre from the drivers seat. If I'm not very much mistaken you can on a Nissan which has a genuine TPMS with individual sensors relating to each tyre. The Honda system is a Deflation Warning System and doesn't specify which tyre is faulty. Has this been adopted to cut costs?

And, I hardly need to add, these systems need to be robust and not prone to false alarms.

[culzean]

I agree with andruec on this one. Ideally you want to be able to access the pressure in each tyre from the drivers seat. If I'm not very much mistaken you can on a Nissan which has a genuine TPMS with individual sensors relating to each tyre. The Honda system is a Deflation Warning System and doesn't specify which tyre is faulty. Has this been adopted to cut costs?

And, I hardly need to add, these systems need to be robust and not prone to false alarms.

Many of the car makers use indirect (ABS) TPMS,  the shear faffing around with sensors and potential damage to sensors when fitting tyres, not to mention people who change wheels for the winter and summer (a lot of European countries)  need more sensors (at a cost) and they have to be programmed in (maybe at a cost as well).   Any car over 8 maybe 10 years (max) will need new sensors as well as the batteries are part of the sensor and cannot be replaced.

Quote........ 

Since factory installation of TPMS became mandatory in November 2014 for all new passenger vehicles in the EU, various iTPMS have been type-approved according to UN Regulation R64. Examples for this are most of the VW group models, but also numerous Volvo, Opel, Ford, Mazda, PSA, FIAT and Renault models. iTPMS are quickly gaining market shares in the EU and are expected to become the dominating TPMS technology in the near future.

iTPMS are regarded as inaccurate by some due to their nature, but given that simple ambient temperature variations can lead to pressure variations of the same magnitude as the legal detection thresholds, many vehicle manufacturers and customers value the ease of use and tire/wheel change higher than the theoretical accuracy of dTPMS.

[andruec]

I wonder if the LED/laser reading could also be used to detect pressure changes? It probably isn't beyond the realm of possibilities for a computer to monitor the shape of the tyre and as well as detecting low tread depth, detect shape changes indicating low pressure.

[culzean]

I wonder if the LED/laser reading could also be used to detect pressure changes? It probably isn't beyond the realm of possibilities for a computer to monitor the shape of the tyre and as well as detecting low tread depth, detect shape changes indicating low pressure.

Anywhere around wheel arch area optical sensors are going to be continually bombarded and coated up with dirt and cr4p off the road.   

Cars would be a lot safer if basic maintenance and observation were part of the driving test,( has been since 2017 apparently but don't know how deep it goes)  at least prospective drivers would have some idea about how a potentially lethal piece of equipment like a vehicle works instead of treating it like a toaster or other household appliance.