I have been worried why my tubed tyres always lost pressure over a few weeks and have found this article from Bennetts insurance which would seem to explain why modern tubes leak a bit of air.
Years ago tubed tyres would keep their pressure for months or years – many barn finds still had the tyres fully inflated.
So it seems that fitting new tubes on my Vincent to stop the slow deflation was probably a waste of time and would explain why even my tubed tyres on the Suzuki lose some pressure in a week or two.
Please see the extract below from an article, though the full text can be seen on the link at the end of the email
What is the difference between tube and tubeless tyres?
Simply put, a single layer of material on the inside of the tyre’s carcass.
All the materials used in a tyre are about performance – a balance of grip, flexibility and durability. It may surprise you to hear that the ideal mix of rubber is actually porous, so will slowly leak air. In the past, this was overcome by fitting a tube with a completely different rubber mix that would contain the air much better and have little effect on the overall performance of the tyre.
The biggest issue with this design is that if it’s subjected to a puncture, the tube will lose all of its air suddenly, which would have typically escaped rapidly through the spoke heads on the wheel. Rapid deflation of a tyre on any vehicle is not good, particularly when travelling at speed.
Created predominantly with safety in mind, the tubeless tyre was designed by taking a section of tube material and making a single continuous layer on the inside of the tyre carcass, and also saving weight.
Of course, a tubeless tyre can still be punctured, but the offending object usually stays stuck in the tread and the tyre deflates slowly, giving the rider an opportunity to slow down. At the same time, cast wheels mean spokes are no longer needed, so the entire unit has become sealed.
Now, instead of manufacturing both tubed and tubeless tyres in the same size, most companies only make tubeless, and recommend that tubes can be fitted if required. The disadvantage to this is that it adds additional weight to the total wheel assembly, which can lead to more heat generation, which ultimately means faster tyre wear.
If a tyre states that it is ‘tube type’, then it will have no tubeless liner, so it will not hold air and therefore must be fitted with an inner tube.
All the best