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low pressure one tyre, no obvious damage

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Mrklaw

Active Member
Mar 5, 2020
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1,734
Berkshire
Not had my car that long, and a couple of weeks ago I got a low pressure warning in the rear drivers side tyre. It was showing 36psi vs the 44 on the others (guess they were over inflated from delivery). I can't see anything obvious wrong with the tyre - no big screw/nail in it. I topped up to 42 and it dropped again over the next few days back to 36. If it has a slow puncture would it go further than that, or perhaps depending on the puncture it might stabilise at a lower pressure?

I'll drop it in to a tyre place but would like to see if there is anything else I can try first. If they replace the tyre, do I need to do anything with the pressure sensor?
 
Could be a tiny hole to lose air that slowly. Could also be the valve (they can unscrew the core and replace I believe).

Tyres are repairable if its away from the edge, they may try and say they're not if they have the foam lining, they just need to cut a hole in the foam and patch it.

Any self respecting tyre place should be fine with the TPMS valves, they're pretty common now. Just drive for a few miles after any work to get the pressure to read.
 
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Put a bit of spit on the valve opening. If it bubbles, its got a bit of a leak - not uncommon and can often be fixed with blowing a bit of air through it and/or pressing the valve insert itself.

When I top up tyres as a matter of course I put a bit of spit on the valve before putting the dust cap back on just to make sure its not leaking before it becomes an issue.
 
42 to 45 PSI is about right pressure wise, some drop the pressure to 40 and others 45 ish - its reputed to change the ride quality - especially if you have the 20" wheels and performance, personally i inflate to 44 psi. I don't find any difference in the way the car rides or feels, then again I have had quite a few performance cars and all had firm suspension and low profile tyres.

Clearly you are loosing pressure, now that could be something that punctured the tyre that was fixed to the ground - so it was an in and out so no evidence of a screw or nail - for example a plank of wood with nails protruding - drive over it and its an in and out.
Of course it could be the valve or even the tyre not sealed to the rim of the wheel - has the tyre been changed at some point? - That's the reason they dawb your tyre with soap when they fit them - it allows the tyre to slide easily and snug up to the rim to seal.
Alloy wheels can also allow air to seep through the alloys and the reason some people inflate with nitrogen - it has bigger molecules so a porous alloy doesn't allow pressure to escape, The tyre itself can also become porous .

Most likely is a puncture then an ill fitted tyre, wheel off and dunk it in a kiddies paddling pool will reveal if any air is seeping out - and that's what a tyre place will do - bung it in a tank to check. (and the dishonest ones will tell you a new tyre is the only option before doing any checks).
 
36PSI is underinflated though. Underinflation causes premature aging of the tyre as it introduces heat changes from excessive flexing and that leads to cracking on the sidewall, plus the centre section of the tread wont be in good contact with the road - so the performance also drops off.
£6 psi isn't massively under and probably wont affect anything you will notice, but the tyre wont drop from 44 to 36 and remain there - it will continue to drop.
 
Not had my car that long, and a couple of weeks ago I got a low pressure warning in the rear drivers side tyre. It was showing 36psi vs the 44 on the others (guess they were over inflated from delivery). I can't see anything obvious wrong with the tyre - no big screw/nail in it. I topped up to 42 and it dropped again over the next few days back to 36. If it has a slow puncture would it go further than that, or perhaps depending on the puncture it might stabilise at a lower pressure?

I'll drop it in to a tyre place but would like to see if there is anything else I can try first. If they replace the tyre, do I need to do anything with the pressure sensor?
I had exactly the same problem on the same corner a couple of weeks back. Was dropping about 2-3PSI every week . When it got to 38 I topped up but haven't needed to this week so may well have been the valve that was corrected by inflating? I'll keep an eye on it.
 
I've had this twice on my M3, both times it was a screw. The pressure would go down from 42psi to about 34psi then stabilise. I believe there was enough 'pressure' when fully inflated to push air out around the screw, as the pressure reduced, so did the gap, hence stabilising.

Before now I have actually put a screw in a hole in a tyre and tightened it to stem a leak and drive to the tyre place...
 
Ok was a puncture and behind the foam so Kwikfit fit not wanting to repair and I’m not fussed to push on it. They did have a replacement in stock which is good, and they said they have rolled out the jack pucks across the company now the model 3 is more common

Expensive tyre but compared to my BMWs 19” run flats it’s relatively affordable. Just a pain only 2 months into the car
 
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Fingers crossed you had the tyre returned to you. All the foam can be removed from it and then no one would refuse to repair it. I would then keep my eye open on ebay, preloved, schpock gumtree, facebook, for someone selling a wheel that matches and have a spare wheel and tyre ready to put on, the boot is big enough for it to live there - and if your really OCD then you could make a frame to completely cover the spare wheel and carpet it - thats what i would do.
 
Put a bit of spit on the valve opening. If it bubbles, its got a bit of a leak - not uncommon and can often be fixed with blowing a bit of air through it and/or pressing the valve insert itself.

When I top up tyres as a matter of course I put a bit of spit on the valve before putting the dust cap back on just to make sure its not leaking before it becomes an issue.
An alternative to spit is to acquire some 'Leak Detection Fluid.

I've worked in various industries and remember chatting to a gas fitter years ago who was pressure testing a system with a squirty bottle of 'Leak Detection Fluid.

Turns out LDF in this case was a solution of washing up liquid, works a treat, follow the bubbles.
Fingers crossed you had the tyre returned to you. All the foam can be removed from it and then no one would refuse to repair it. I would then keep my eye open on ebay, preloved, schpock gumtree, facebook, for someone selling a wheel that matches and have a spare wheel and tyre ready to put on, the boot is big enough for it to live there - and if your really OCD then you could make a frame to completely cover the spare wheel and carpet it - thats what i would do.
Good advice Glynn,

Would that work with a Boxster as well 😉
 
I've had 2 punctures on my MY one on each rear a week apart. Less than 2k miles. Took the first to 'National' who are a chain and they didn't want to repair as under foam - they did after a little bit of 'I will give you cash mate'....

Second one I took to an independent - he was much more knowledgeable about Tesla's generally and was more than happy to fix the puncture under foam. I will use him for new tyres when needed..
 
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Fingers crossed you had the tyre returned to you. All the foam can be removed from it and then no one would refuse to repair it. I would then keep my eye open on ebay, preloved, schpock gumtree, facebook, for someone selling a wheel that matches and have a spare wheel and tyre ready to put on, the boot is big enough for it to live there - and if your really OCD then you could make a frame to completely cover the spare wheel and carpet it - thats what i would do.

I can't imagine any cash-strapped tyre fitter "operative" would chuck out a valuable tyre that can be so easily and safely repaired. If it hasn't gone back to the customer I suspect it will end up being repaired and used .. or sold to a mate.
 
Pressure dropped again yesterday. Had the tyre off and looked like a stone that had lodged itself caused the issue.

Called a few tyre places that said "you can't fix those foam tyres". Found a place and actually turned out I had a piece of glass slowly eating its way through!

If you've got the same issue and are local, I'd definitely recommend Tyre Pros in Milton Keynes.
 
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Pressure dropped again yesterday. Had the tyre off and looked like a stone that had lodged itself caused the issue.

Called a few tyre places that said "you can't fix those foam tyres". Found a place and actually turned out I had a piece of glass slowly eating its way through!

If you've got the same issue and are local, I'd definitely recommend Tyre Pros in Milton Keynes.
Oh... and they have pucks 👍
 
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