Pressure testing innner tubes

[Mick F]

I bought a pair of Schwalbe inner tubes recently, and their blurb says they'll stay inflated longer than normal tubes.
viewtopic.php?f=5&t=46540

CJ sent me a challenge, but until now, I haven't had a decent enough pressure gauge.
I have now, so here we go!

So it'll be interesting if MickF would like also like to engage in long-term pressure retention experiments.

I've a pair of spare wheels and put a Schwalbe Tube into one, and a Vittoria Ultralite Tube into the other.

I've inflated them to exactly 100psi as indicated by my new gauge and I'll check them again every 24 hours and report back to this thread.

Any bets for what I might find?

[meic]

I would have more confidence in a weekly check of the tyre pressure as every reading you take will possibly release more air than is lost by seepage.
You can always do that next time.

[hubgearfreak]

Any bets for what I might find?

yes - something statistically worthless that has the danger of turning into unhelpful urban myth

take 250 tubes from each manufacturer and test each one. work out a way of determining pressure without losing pressure (such as measuring indentation for a given force) and then you may find out something interesting, or at least worthwhile

[BigG]

I think it would be better to check just once after one or even four weeks. A single check avoids the problem of letting air out while checking. Incidentally, I have always assumed that leakage through the valve was the biggest problem. Has anyone any information on this?

[hubgearfreak]

I have always assumed that leakage through the valve was the biggest problem. Has anyone any information on this?

schwalbe tubes have certainly had this as an issue, for me. occasionally the valve screws more firmly to the cap than the metal tube in which it lives.

[Mick F]

My new gauge doesn't let much air out at all. Even with Presta, which is surprising. This is the gauge:
http://www.chainreactioncycles.com/Mode ... delID=8504
Not cheap, but I can use it on the car and trailer with Schreader far easier than the pencil-thingy-with-a-spring-in-that-has-a-plunger-that-comes-out - - you know the sort - awful!

This one beeps when it's got the pressure reading, it has a light on it so you can see the valve, it records and stores the reading until you press 'clear' and it comes with a spare battery.

It's actually quite good, so I'm pleased.

Anyway, I reckon a week is too long, but if you insist, I'll report back a week today and leave the spare wheels alone.

Before anyone asks where they are and if the temperature is going to vary - they're in the spare bedroom, unheated and in an even temperature also out of draughts.

[meic]

"No varying temperature AND out of draughts. Hardly a real life test makes the results totally useless."

[Mick F]

No, not Real Life!

If I were to do Real Life, I would have to use the wheels every day, but that would ruin the test because I would have to top them up each time I went out - like I usually do - thereby negating any info about pressure retention.

This is just a static test.

[cycleruk]

As long as the wheels are next to each other then I would accept any temperature variation being reasonably equal to both.
I would ask though are both rims and tires the same?
I could imagine if the tires are different then there may be a chance that the tire could help with sealing the air in the tube.
Anyway the results will be interesting to see.
As most of us carry pumps then leakage isn't to much of an issue. I do find, generally, that I check and top up my tubes about once a week.

[Mick F]

They are a pair of Mavic MA3s on Campag Mirage shod with an identical pair of 22mm 700c Nutrak tyres.

[prm]

I’ll go for 0.5-1% reduction per day.

What’s the prize?....... Your old tubes!!!

[Mick F]

No prize, just a warm feeling of being right!

1% per day would make 7% in the week? ie 100psi down to 93psi?

From experience of topping my tyres up every day or two, I'll bet you are way out. I'll bet that by Tuesday afternoon 15Th Feb - 1 week after starting this test and not touching them at all - they will be down to 75psi or even lower.

I also reckon that Schwalbe are telling porkies about their tyres not needing to be topped up for 30 days. Poppycock IMHO.

[hubgearfreak]

I also reckon that Schwalbe are telling porkies about their tyres not needing to be topped up for 30 days. Poppycock IMHO.

that'll work for normal people on 42mm tyres who really don't mind if their tyres are at 70 or 55 psi.
of course, if you're an 11 stone athlete on 23s to whome every second matters, then you wouldn't be buying schwalbe extra thck rubber in the first place
halo sell 3mm walled tubes at a £tenner a pop, but only for small wheels http://www.halorims.com/products-detail ... d=TUHAD41S

[Mick F]

Ah, but Schwalbe don't differentiate about their differently sized tubes. I bought a pair of 18-28mm and they came with the glib statement they would go for 30 days.

They never said anything about them being slower or heavier or thicker. They said the material they are made from is superior.

Sorry, lost the leaflets, but read this:

Slightly different to their leaflets, but they still say that than some brands will lose nearly twice as much as their tubes.

[meic]

No prize, just a warm feeling of being right!

1% per day would make approximately 7% in the week? ie 100psi down to 93psi?

From experience of topping my tyres up every day or two, I'll bet you are way out. I'll bet that by Tuesday afternoon 15Th Feb - 1 week after starting this test and not touching them at all - they will be down to 75psi or even lower.

I also reckon that Schwalbe are telling porkies about their tyres not needing to be topped up for 30 days. Poppycock IMHO.

Bearing in mind our recent threads on percentages and innumeracy.