How do flat tyre sensors work

Geoff.D said:
So that means tyre rotation now involves removing the tyres themselves from the rims and rotating just the tyre? What a completely stupid idea! Just because of a poorly implemented very useful function by car manufacturers that refuse to provide the means for owners of vehicles to take control of automated systems?
Like I said, automation in vehicles ostensibly done to "improve" reliability and safety is actually a process of turning all drivers into the dumbest of individuals. The LCD problem all over again.
As @ToxicBunny posted, "drivers are morons" therefore treat ALL drivers as if they are morons. The outcome is a self fulfilling prophecy drivers are slowly becoming mindless idiots that just happen to be sitting in the driver seat.
Click to expand...

I think the moron issue is considerably more widespread that just the drivers, its a general dumbing down of the populations at large. I wouldn't say treating drivers as morons is making them mindless idiots, the motor manufacturers are responding to what is an existing phenomenon that is happening outside of their control.
 
neoprema said:
Most of my Renaults had tyre pressure monitors and the manuals all said something along the lines of "rotating tyres is a needless exercise that will cause the tyre pressure system to stop functioning correctly and provides negligible gain in the lifespan of tyre tread."
Click to expand...
So, what do you need a spare wheel for? What does that system do when you fit a spare?
 
Let me just leave this here..
 

Attachments

  • stop-the-government-from-tracking-your-car-disable-the-tracking-61571818.png
    stop-the-government-from-tracking-your-car-disable-the-tracking-61571818.png
    161.3 KB · Views: 10
Geoff.D said:
So, what do you need a spare wheel for? What does that system do when you fit a spare?
Click to expand...
It would just complain the whole time that the wheel could not be found. (usually a flashing X over the wheel or just the wheel icon would disappear and service light come on.
 
Didn't some vehicles also use infrared beams to monitor tyre rotation to detect a flat tyre (not so much actual pressure) ? I remember reading once about tyre pressure monitoring that didn't need anything in the wheel but you HAD to stick to the factory fitted rims and tyre spec or it would not work (as I'm guessing it has set calculations for measuring).
 
Geoff.D said:
So, what do you need a spare wheel for? What does that system do when you fit a spare?
Click to expand...

The spare does not have a sensor.

As to what the system does in those situations, after about 3km it will alert you that it is not able to monitor that wheel.
IMG_20181207_161151_1.jpg

In this case the valve stem on my front left wheel was broken off and I had it replace with a normal tyre valve while I waited for the replacement valve stems to arrive from eBay.
IMG_20181008_082724_DRO.jpg
If you look closely you will see a piece of metal that attached to the valve stem (also metal) that is because the valve stem acts as antenna for the sensor.

They operate at 433MHz which is the same frequency they key fob remote uses.
 
neoprema said:
Didn't some vehicles also use infrared beams to monitor tyre rotation to detect a flat tyre (not so much actual pressure) ? I remember reading once about tyre pressure monitoring that didn't need anything in the wheel but you HAD to stick to the factory fitted rims and tyre spec or it would not work (as I'm guessing it has set calculations for measuring).
Click to expand...
That system usually used data from the ABS wheel speed sensors fitted to each wheel to calculate the rotation of each wheel & if any one of them was providing a different reading, that would indicate that that particular tyre was deflating & was now a different diameter to the other 3 wheels, thereby causing the discrepancy in the data streams to the ABS unit.

That is why these TPMS systems only function correctly if the OEM wheel & tyre combinations are used, as that is what the ABS unit has been calibrated for in order for the correct data sets to be provided by the ABS wheel speed sensors.
 
True - and for some reason it is law that all new cars sold in the US must have TPMS.

Forgot to add, before the car realises that the wheel has no sensor it first shits itself thinking you have a massive nail in it. I have seen that once before, if the pressure is lower than expected you get the orange ( ! ) and if it gets close to 1 bar it goes red and tells you to stop.
 
Ivan Leon said:
That system usually used data from the ABS wheel speed sensors fitted to each wheel to calculate the rotation of each wheel & if any one of them was providing a different reading, that would indicate that that particular tyre was deflating & was now a different diameter to the other 3 wheels, thereby causing the discrepancy in the data streams to the ABS unit.

That is why these TPMS systems only function correctly if the OEM wheel & tyre combinations are used, as that is what the ABS unit has been calibrated for in order for the correct data sets to be provided by the ABS wheel speed sensors.
Click to expand...
Ah ok interesting. I was thinking it was some kind of beam spread that checked to see how much tread crosses it say every 1mm beam spread or so.
 
Gaz{M} said:
FWIW I got a puncture in my Tiguan recently and the Tyre pressure warning comes on, the car beeps and shows the tyre pressure diagram on the main screen with all the pressures displayed. Then I watched as the pressure in one tyre decreased by 0.1bar every few seconds. Scary, but a very good feature because I wouldn't have noticed the tyre deflating at the rear, before damaging my rim. It also gave plenty of time to find a place to pull over. VW roadside were excellent! :thumbsup:
Click to expand...

Same thing happened to us. used the rate of pressure drop to note how severe the loss was. drove straight to a tire shop
 
Geoff.D said:


Illustrates the value of the system perfectly!
Why could you not just get out and fit the spare yourself?
Click to expand...

Coz I'm a lazy keyboard warrior and I had free roadside assistance. Why get dirty for no reason?
 
upup said:
I guy told me his flat tyre warning came up, he did replace a tyre. Dealer told him you should have the same tyre, eg both new for sensors to work, I thought there is something measuring pressure
Click to expand...

Two different kinds.

1. Cheap - Uses the ABS sensor rings to detect a difference in rotation between different wheels. Not as accurate but basically costs nothing. It provides no pressure detail only that one tyre differs dramatically from others.

2. Expensive - Actual sensors sit inside the tyre attached to the inside of the valve. They have batteries in and activate usually when going over 20km/h or so and then report the actual pressure wirelessly to the car. Very accurate but expensive to install and also expensive to replace every few years when the batteries die.

The fact that the tyre needs to be the same size (not same tyre) tells me it's the cheap system in place.

Needs to be the same size regardless for all the other systems in play to work properly anyway.
 
Ivan Leon said:
For almost a decade now of car ownership, I have taken my car once a week to the local Caltex service station near me - usually a early on a weekend morning before I go shopping - as they have digital air pressure displays for their tyre inflation hoses - and I make it a habit to also check the spare tyre as well.

The sticker with the manufacturer recommended tyre pressures for the OEM tyres (175/60R14) is 230 kPa for the front & 190 kPa for the rear tyres, but because I have slightly higher profile tyres fitted (175/65R14) I normally bump up the pressures by another 20 kPa, which seems to improve both the ride & handling characteristics when compared to the OEM settings. I also inflate the spare wheel to 250 kPa as well.

Before I drive out to the service station, I also pop the bonnet & check all the various fluid levels - oil, coolant, power steering, brake master cylinder & windscreen washer - and top any of them up if they are lower than normal.

At the end of this month I will also be taking my car for its 10,000 km tyre condition check - which also includes rotation, balancing & wheel alignment - so that I even out the tread wear on all 4 tyres as equally as possible.
Click to expand...

Unfortunately even those digital ones are woefully inaccurate (sometimes dangerously so) and I would recommend always carrying your own pressure tester to compare and then simply fill up accordingly or over pressure and blow down.

Of course with TPMS you can just use those values as they are calibrated for a given temperature anyway and then the hot/cold thing isn't such an issue either.

But yeah I've always used the highest values the manufacturer recommends all round for a bit faster steering and generally better wear. With modern tubeless tyres you can't really cause any problem with the tyre wearing down the middle and they can take something stupid like 18bar before they pop.
 
Geoff.D said:
I don't rotate the tyres --- great for even wear but it means ALL the tyres are buggered at the same time.
I have two spares and rotate the tyres Spare to back, back to front, front into spares --- means I replace only two at a time. (Left stays on the left, even the spare are marked LHS or RHS).
And besides, I can pick up abnormal wear on a tyre within about 2 000 km. ( every 15 000 km works for me).
Click to expand...

On a 4x4 it really shouldn't matter as they should all wear down the same regardless if rotated or not. (Weight being left out of the equation of course which will affect it somewhat).

On a FWD or RWD though rotation is exactly what will allow for only replacing two at a time if done at regular intervals and you'll get further across the entire set.

Unless you have one of those fancy BMW's you hate so much, then the rears and fronts are different sizes and you have no choice in the matter regardless.
 
SauRoNZA said:
But yeah I've always used the highest values the manufacturer recommends all round for a bit faster steering and generally better wear. With modern tubeless tyres you can't really cause any problem with the tyre wearing down the middle and they can take something stupid like 18bar before they pop.
Click to expand...
I stopped doing that for precisely that reason. Eco mode might have saved me some petrol but tyres weren't lasting.

762974
 
You must log in or register to reply here.
Back
Top
Sign up to the MyBroadband newsletter
X