Tyre pressure.

[Stevey101]

Hello guys.
So I have an F83 M4 comp. Now my rear tyres keeps losing pressure, I fill them up to 40psi and after only 2 weeks they drop to 34psi and it’s both tyres the exact same. They lose about 5/6psi every few weeks and I only drive my car 2/3 days a week so it just seems a bit excessive?
I could be wrong and this could be totally normal as I’ve not had the car that long. It doesn’t seem like a slow puncture or anything as it would go lower than that and also it’s both rear tyres at the same time.

Thanks

[HasToBeV8]

Are you filling them at same temperature? Tyres typically do go up a few psi when driven/hot, although 6psi seems quite a lot (2-3psi more normal, unless you're doing repeated burnouts!).

Either that or you have been very unlucky and got two identical slow punctures

[Stevey101]

Yeah getting filled up at the same temp

[Fady]

HasToBeV8 said:

Are you filling them at same temperature? Tyres typically do go up a few psi when driven/hot, although 6psi seems quite a lot (2-3psi more normal, unless you're doing repeated burnouts!).

Either that or you have been very unlucky and got two identical slow punctures

Or possibly leaky valves.

[Huff]

Oh - and - get the rims checked, too: even /slight/ deformation in a rim bead can lead to pressure sim loss (says an ex - Alpina owner..)

[Maxym]

I heard once that old alloys can get porous and leak air that way. Dunno if true.

[uktrailmonster]

Is this something that has just started happening spontaneously or after a new tyre fitment or some other notable event?

[Stevey101]

uktrailmonster said:

Is this something that has just started happening spontaneously or after a new tyre fitment or some other notable event?

It’s been happening since I’ve had the car tbh, but with it been a performance car I thought It might just be normal.

[uktrailmonster]

Stevey101 said:

uktrailmonster said:

Is this something that has just started happening spontaneously or after a new tyre fitment or some other notable event?

It s been happening since I ve had the car tbh, but with it been a performance car I thought It might just be normal.

In that case I would say you have leaky wheel rims. Next time you change tyres I would get them inspected for cracks.

[sherman]

I would take it to your local decent tyre fitter and ask for the tyres to be reseated.
Ask for the wheels to be be cleaned back properly and then put back on with lots of fresh tyre soap.

2 tyres should be no more than £50 to reseat.

[NRG1976]

Stevey101 said:

uktrailmonster said:

Is this something that has just started happening spontaneously or after a new tyre fitment or some other notable event?

It s been happening since I ve had the car tbh, but with it been a performance car I thought It might just be normal.

On my f80 m3 I probably top up the air once a year during winter when temps drop and air contracts as a result and that s it. Should not be losing pressure really.

As an aside why are you going up to 40psi, most owners go up to mid 30s ?

[Stevey101]

uktrailmonster said:

Is this something that has just started happening spontaneously or after a new tyre fitment or some other notable event?

It’s been happening since I’ve had the car tbh, but with it been a performance car I thought It might just be normal.

[ARHarh]

take the car to a local independent tyre shop shop and tell them you are losing air, they will pop the tyres off and clean the rims before refitting your tyres. Or if the rims are prone to leaking they will tell you that as well.

All rims corrode over time and unless the tyre fitter cleans the rim with a whizzy wheel thing they will leak.

[E-bmw]

sherman said:

I would take it to your local decent tyre fitter and ask for the tyres to be reseated.
Ask for the wheels to be be cleaned back properly and then put back on with lots of fresh tyre soap.

2 tyres should be no more than £50 to reseat.

^^^^ Wot 'e said.

Most likely they weren't cleaned at the last tyre swap.

[Smint]

First of all i'd whip the wheels off and stick them in some clean water to find the leaks, soapy water splashed liberally in the tyre and bead area should show if its puncture or bead leaking but if the wheel itself is leaking you'll need it sitting in still water for a while to spot the tiny flow of air bubbles.

Paying someone to reseat them only to find some low life who disliked the previous owner had stuck a braddal or similar through each sidewall would be annoying.