Tyre pressures

[Fordulike]

Last time i pumped up and checked my tyres was about a month ago.
They're both Marathon Pluses and pressured to 65psi (70 is the tyre's max).
After my battery issue, i forgot to check the pressures, as i was deperate to get out and about again.
After riding, it felt a bit soft and spongy so i checked them out.
Both tyres have dropped to around 42psi.
I know that all tyres naturally lose air and require regular pumping up, but is 20 odd psi normal to lose in a month.
Strange that they have both lost the same amount which rules out a puncture.
Can anyone put my mind at rest?

 

[Vikki]

Quite normal.

I've had mine at 60 psi and after 3-4 weeks thought they felt soft and found them to be anywhere between 30 to 35 psi.

Air is sneaky stuff, sniffs out molecules and squeezes between them (probably goosing a few on their way through ).

Best check 'em, once a week - but who does? OK, some will, but most of us forget

Vikki.

 

[Mussels]

That isn't unusual and it's what happens to my MP tyres. I'd have thought it has more to do with the inner tubes than the tyre but other tyres don't seem to go down as quick.

 

[Vikki]

Oops! Didn't spot he mentioned tyres. It's the tubes. Tyres don't come into it since the airloss over time will exit via the spoke nipples.

I wonder what the rate of passage is for air through rubber?

Vikki.

 

[Fordulike]

Sorry i did mean through the inner tube.
Just mentioned the tyres for reference to the high tyre pressures.
Sorry for the confusion.
Glad to hear it's normal
As for goosing molecules... that sounds rude, no explanations please

 

[Vikki]

I've heard that some of the rubber molecules quite like a goosing from an air molecule and that leads to little romances going on throughout the rubber and that's what slows down the airloss Good job they don't go too far or the rubber would start getting plumper

Vikki (off in a little world of her own at times - yes, this is one of those times).

 

[Fordulike]

You should be out riding yer bike in lovely weather like this...... in fact so should i
I'm gone.....................

 

[Vikki]

I'm stuck at work.... waiiiilllllll

 

[flecc]

Anytime you replace tubes, look for low loss types like those Schwalbe make, they don't cost any more. The difference isn't dramatic but they do help a bit.
.

 

[CeeGee]

Heat can affect the pressure in a tyre/tube, although it would have to be a rather large difference in temperature to make a difference of 20psi.

Colin

ps: The valves are often the problem of air loss.

 

[thunderblue]

what a relief ..... I always thought it was my weight causing the problem!

 

[Old Timer]

20lb loss in a couple of weeks seems a bit much to me, time for new tubes me thinks like the ones that Flecc suggests.

Mine loose about 10lbs in about three months.