How does the TPMS system work without tyre sensors?

[NaweedMustafa]

Just want to gain some knowledge as i was a bit confused. So i havent had TMPS sensors since i bought the car, didnt bother purchasing them, when installing the new tyres. i presumed it was deactivated via coding as ive never got any error saying it cannot read the tyre pressure.

The other day, while i was driving, the red tyre pressure warning came up. I thought about disregarding it because i knew i didnt have the sensors however, at the back of my head i decided to pull up to a gas station and check the tyre pressure. Lo and behold, my front left was at 1.6bar (23PSI). filled it up and held the tyre pressure monitor button to store the new values.

My question is, what kind of wizardry is going on for it to know that something is up? is it only for my front wheels that it can somehow measure the deviation in height when the delta is quite high?

I really thought i just didnt have any tyre monitoring going on in the car without those little sensors.

 

[enuff_zed]

When you press the button to calibrate the sensors it merely measures the rotational speed of each wheel and sets it as a datum. Then if the pressure drops the diameter reduces and the speed changes and it lets you know. Therefore it is accepting whatever pressures you start with as the datum, whatever they are

 

[NaweedMustafa]

Aha, makes sense now. Thanks! My mechanic was telling me it was the suspension sensors detecting the tilt but i wasn't convinced...

 

[j3nks79]

Aha, makes sense now. Thanks! My mechanic was telling me it was the suspension sensors detecting the tilt but i wasn't convinced...

Lol that doesn’t inspire confidence.
Rolling Radius

 

[smorris_12]

Lol that doesn’t inspire confidence.
Rolling Radius

It's tolerance is higher than an actual pressure sender so it takes more of a drop to set it off, but considering they hassle and cost of sensors, it gets my vote. I suspect that it's probably more on the ball when used with high profile tyres but I've managed 30 years of driving without either system so I don't see a problem.

They only failure point of the system is that if all 4 wheels go down at the same rate it won't notice. Which was the case when I picked up my Z. They were all about half pressure when I went round the next day with a gauge.

 

[NaweedMustafa]

They only failure point of the system is that if all 4 wheels go down at the same rate it won't notice

I would be absolutely unlucky if I got a screw in all 4 wheels. Luckily it was just the front left

 

[Mr Tidy]

I may be wrong but I think some sort of TPMS was compulsory for anything fitted with run-flats.

The wheel-speed system on E85/86s may not be as accurate as the ones with the valves like later E89s but it seems simpler, and less expensive!

 

[NaweedMustafa]

It definitely saved me. Detection was activated when front left hit 1.6Bar. I did drive down the highway with that pressure hopefully I didn't cause any damage to the tyre, I'll find out tomorrow