Probably a daft question: bicycle sized dust caps on car wheels?

[JP_]

A week ago I had a new tyre fitted.
Was driving for a week before noticing that the dust cap was missing.
Having no spare, I took one from a bicycle in the shed.
Overnight I lost about 10psi (31 down to 20).

Have repumped, and loosley put the cap back on. Hoping that the cap was just too small, and allowing a tiny bit of air to be released.

Does this sound likely? I will probably find out when I get out of work to go home ...

 

[Mottie]

Standard bike valve dust caps are the same as cars (Schrader). The presta valve caps from a bike wouldn’t fit on a car valve. Tighten it up - if your car valve is leaking, the cap acts as a secondary seal.

 

[JP_]

But hang on. Time got away with me. Statement says I got the new tyre on the 5th July.
So I was driving it with no cap for 18 days OK, and then in less than a day of putting that cap on (yesterday afternoon) it loses air. Must be the small cap pushing the pin down, surely?

 

[footprints]

Sounds like a faulty valve to me, dust cap is just that, to keep dirt out.
Take it back to the garage,
Just say it is loosing pressure.

 

[Brigadier]

So I was driving it with no cap for 18 days OK, and then in less than a day of putting that cap on (yesterday afternoon) it loses air. Must be the small cap pushing the pin down, surely?

Correlation does not mean causation.

As a dust cap is domed, I would say it is nigh-on impossible for it to press on the (Schrader) valve pin.

 

[Alec_t]

Have you checked for a puncture?

 

[Munroast]

you say fitted on the 5th July !
when Labour took power, and you're surprised its not working properly

seriously though, have you got a picture of the valv and the valve cap ? just in case you are trying to fit a presta cap on a shrader valve

 

[Mottie]

just in case you are trying to fit a presta cap on a shrader valve

Neither cap would fit on the other.

 

[Munroast]

Neither cap would fit on the other.

No, but with a lot of perseverance you may get a presta inside a shrader, and that would cause your tyre to go flat - never underestimate what can happen

 

[Mottie]

Yeah anything is possible but you'd have to be a right dimbo to do that though.

 

[Munroast]

Yeah anything is possible but you'd have to be a right dimbo to do that though.

I hope @JP_ forgives me for jesting, I really don't think that is what he has done

 

[carmanmemoranda]

Correct the tyre pressure. Keep the valve cap off. Check pressure in a week .

Or go back to fitters and just say it keeps losing pressure

 

[JohnD]

swap the suspect cap to a different wheel, and put the known correct one on your suspect wheel.

 

[norseman]

Commercial dust caps are good as they contain an O ring which makes for a secondary seal, only downside is that they are usually yellow.
Have you tried the old trick of applying spittle to the valve to show up any leakage?

 

[ReganAndCarter]

you say fitted on the 5th July !
when Labour took power, and you're surprised its not working properly

Expect problems with inflation!