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-   -   Only 1 tyre's pressure drops over 15 days (https://www.team-bhp.com/forum/tyre-alloy-wheel-section/294423-only-1-tyres-pressure-drops-over-15-days.html)

My parents get their DZire tyre filled at 30ps pressure every 15-18 days.
However, only one of the tyres (rear, non-driver) gets low to around 12-15ps in 15-18 days of refill cycle. Rest all 3 tyres (including the spare one lying in the boot) are found to be at 26-27ps at the same time.

1) The tyre in question has been checked twice for any minor punctures. Nothing is found. Its all perfect.
2) Mostly driven by the parents in the city, they hardly feel any issues while driving.

Any inputs on what could be going wrong?
How can the same digital pump measure (at two different reputed petrol pumps) keeps showing low pressure in only 1 tyre, and similar intact in remaining 4? What more can be checked?

Thanks

Assuming these are tubeless tyres, have you checked for leaks on the side walls or near the rim? Often there will be leaks from where the rim meets the tyre and local shops never check this.

That tyre might have developed small cracks that are causing this. Exact same thing happened with our car tyres. All tyres were ok, except the left rear one, consistently used to show much lower tyre pressure when filling up. Couple of tyre centers said it was because it had developed cracks. In our case, the issue was very, very limited usage. The car was being used once in 2 months, and that too just for the sake of keeping it running.

How old are the tyres, how many km have they run? Is the car being used often?

Since I am very fincky about tyre pressures and super sensitive to it too, I keep checking it once a week atleast and have figured out some pain points which causes this.

1) Usually, tyre pressures when they drop, all tyres have a drip with a maximum difference between them of 1 psi if everything is perfect.

2) When one tyre pressure is lesser by more than 2 psi consequently, something is wrong.

3) Tyre pressure is lost because of the following

a) Valve Pins being leaky or loose
b) Value base having a minor leak
c) Dirt or dust between tyre and rim. Tyre needs to be removed and refitted back after cleaning. Make sure its fit back in the same position on the rim as when removed otherwise balancing will go for a toss.
d) Minor needle type puncture which takes an expert puncture guy to find (I had one like this, use to loose 2 psi only in 1 tyre, rest were 1 psi). I kept going to punture guys and they kept saying its fine its fine but I was not happy, I went to this punture guy, we filled it to 50 psi and kept putting the water solution on the tyre for like 20 minutes until we found this small bubble which had a very half an mm type needle type long thing stuck inside which was leaking minor air.

In your case, half the air is being lost, so its definitely out of the above.

Two of my cars had this issue. First was traced to a valve.

The second was traced after taking the tyre off the car, found to be a the tail of a screw embedded in a tread. Couldn't even see it, almost.

And it did not cause any bubbles when cheeked with water. But it was enough to let out about 3-4 psi over a couple of days.

It is slow leak for sure somewhere. A competent tire repair shop should be able to diagnose it. Depending on your location kindly search for a tire shop on the Team Bhp directory section. If you stay near Santacruz then Trevor from Straight Line should be able to assist. Else look for a place closer.

Good Luck.