Tyres losing pressure.

The front left can go down overnight, to about 10psi, yet on other days, it doesn't lose any pressure. It stayed the same for 6 weeks before Christmas. Then went down to 10psi in two days.

Now the rear tyres are doing the same.

I've even been suspicious that someone was letting them down, but my home made, anti-tampering "traps" on the valve-caps haven't been disturbed.

Any ideas, anyone?

 

Flat spot on an a wheel caused by a pot hole was the culprit in my case.

 

What wheels do you have? any new tyres recently or wheel refurbs?

 

Wheels are WRX '04.
No new tyres, refurbs etc. Tyres have been on a year.

 

If its not something in tyres even something small giving them slow punctures and you haven't got flat spots,then it could be the alloys going porous or corroding on the inner rim where tyre seals. You can have tyres removed,they rub down the inside and put some black gunk around which helps seal it but ideally will need them refurbed or a new set. Take to tyre shop they'll test where the leak is.

 

Yes, I understand all that, but, see, what gets me is that sometimes they go down overnight, other times they can stay at pressure for 6 weeks or so. And the loss in pressure doesn't seem to coincide with temperature, rain, where I park, whether it's been driven or not etc etc.

 

rebead them

 

If the porous part of the alloy is bearing the weight of the car it is more likely to leak. This is perhaps why it appears as an intermittent issue. If the porous part of the alloy is positioned so there's no weight on it it won't leak.
As recommended above get them resealed and see if it cures them.

 

I had an issue on my old set where the wheel was porous. You can get the tyres off and get them sealed when they put them back on. Also check the beads are in good condition.

 

Are you sure there aren't any nails in them? I mean taking them off and rotating all the way round to check?

 

This is the only thing I can see that might be doing it. AFAIK, there are no nails etc in the affected tyres, had them off off to look.