I normally check my tyre pressures once a week and often adjust them for load, so this morning I reduced them from full load 38F 37R to 33 front and rear, normally i reset the tpms but today as an experiment i didnt an suprised that nothing came up as a warning, I thought a 5 psi drop would do something.

I t seems im more sensitive to pressure drops as i can detect 2psi drop

The car is as my profile a 2017 1.5tdci Grand Cmax Titianium.

5 hours ago, pragmatix said:

I thought a 5 psi drop would do something.

I don't know the exact figure but I would guess it is somewhere near 1/2 or 3/4 of the set figure.

The only reason I'm saying this is because I recently had a courtesy for a few weeks which unknown to me had a nail in one of the tyres, so was losing air slowly. When the TPM Light came on during a journey the pressure was quite low, I don't remember exactly but I think it was near 1/2.

I was doing a 300 mile journey at the time so I overfilled the tyre by a few Bar and that did not trip the TPM Light, so I think it is designed for serious underinflation cases rather than an alternative to checking pressures regularly.

The warning is triggered by a 20% pressure drop from the learnt warm tyre pressure value

2 hours ago, iantt said:

The warning is triggered by a 20% pressure drop from the learnt warm tyre pressure value

Thanks, i can feel it better than the tpms can, allways thought they where useless.

The tpms is primarily for the reasonably quick deflation of a tyre while on a journey, therfore warning you before it gets really flat and dangerous to drive. 

I thought the whole point of TPMS being mandatory now was to detect minor underinflation for safety & emissions?  Might as well stick with DDS if it doesn't warn until 20% down! 😮 

On 10/4/2019 at 8:36 PM, iantt said:

The tpms is primarily for the reasonably quick deflation of a tyre while on a journey, therfore warning you before it gets really flat and dangerous to drive. 

Maybe, but you have to be abit brain dead not to be able to feel that sort of thing.

39 minutes ago, pragmatix said:

Maybe, but you have to be abit brain dead not to be able to feel that sort of thing.

Believe me, there's a high percentage of the population who drive that don't know when a tyres flat when driving.