Why don't my Inner Tubes hold air very long?

 For many years, I've heard older people say that inner tubes don't hold air as well as they used to.  It's usually the same thing - 'I never had to air up my tires when I was a kid.'   Others seem to think that tubes puncture easier now than they did even 15 or 20 years ago.  All of this got me wondering if there really is a difference between the quality of tubes and if it's changed through the years.

First, a (very) short history:

 Originally tires and tubes were made from natural latex from rubber trees (Hevea brasiliensis) that are grown almost exclusively in Indonesia and Malaya.  During World War II, Japan had invaded these countries and cut off the world’s supply of natural rubber.  This led to a shortage and the need for an alternative.   At the time, German engineers had already been working on a synthetic rubber, but it wasn't until 1942 that U.S. engineers were able to develop it into a useable rubber compound called Butyl.   Butyl synthetic rubber is the most common material used to make inner tubes today.  

Butyl retains air better and costs much less than natural rubber, making it ideal for inner tubes.  It’s biggest disadvantage is that it doesn’t stretch much - as much as 5 times less than natural rubber. For this reason, Butyl is normally blended with natural rubber to give a tube the ability to stretch more.

The majority of the global supply of Butyl is produced by two companies: Exxon in the USA and Polymer Corporation in Canada.   Exxon offers 5 different Butyl synthetic rubber blends.  Each uses a different mix of additives to allow it to withstand heat better, increase it’s durability, or just lower the cost.  These additives decrease Butyl’s ability to hold air so they must balance these additives for the best compromise.   There are only a few companies that still make tubes in the U.S., but there are easily a dozen or more tube manufacturers in China alone.  These companies blend the different butyl compounds with 10 -20 percent natural rubber in order to give preferred results vs cost.  More natural rubber means the tube will stretch more (which also makes it more puncture resistant)  but it won’t hold air as well.  It also increases the cost.  Again, this is a balancing act to achieve the best compromise.

Other factors that influence how well a tube holds air are the wall thickness of the tube and how closely the tube matches the size of the tire.  A thicker tube wall will slow air leaking; a tube that has to stretch to fit the tire causes the wall of the tube to become thinner, allowing air to leak at a quicker rate.  Thus, thorn resistant tubes with thicker rubber will hold air longer than a superlight tube that uses very thin rubber.   Riders looking to save weight are willing give up a tube's ability to hold air for long periods in order to save a few grams.  This is usually acceptable because these are the cyclists who will air their tires up before every ride.

The chart below shows how different brands of tubes use different thicknesses

Brand/Thckness	Ultralight	Superlight	standard	Thorn reist*
Bontrager	.45mm	.6mm	.9mm	4.1mm/1.2mm
Kenda		.75mm	.9mm	3.5mm/1mm
QBP/Dimension		.73mm	.9mm
Michelin		.7mm	.9mm

*thorn resistant tubes are thicker on the tire side, thinner on the rim side

Back to the original point that brought this up.  Is it possible that tubes held air better 50 years ago?  The answer is yes - the tubes had less natural rubber in them because of the shortage of rubber during and after WWII.  As well, since the tube wouldn’t stretch as much (because it lacked natural rubber), they were made to fit the inside of the tire very close.  This maintained the thickness of the tube, helping them retain air.

Finally, here's a neat YouTube video from the TV show 'How It's Made' showing how tubes are manufactured.

So what can we take away from all this?

There are slight differences in the exact formulas used for inner tubes, and that can affect it’s cost and its ability to hold air.  However, with most U.S. tube suppliers,  it's more likely that the reason one tube holds air longer than another is a result of the thickness of the tube after it stretches to fit a tire.  Pick a tube that fits the tire better (so it stretches less) and/or a thicker, heavier tube to ensure that a tube holds air pressure longer. 

note: this is a (slightly) updated post from my other blog: thebikehive.blogspot.com

What is Kashima Coating?

Kashima coating is a feature currently only found on Fox forks and shocks*.  It's easy to spot because of its distinctive goldish-brown color.  But what is it and why do they use it? 

First, a quick definition:
Anodizing is a process by which a metal part (normally aluminum) is electrically charged and submerged in a chemical bath.  This creates an oxide layer that penetrates the metal and changes the microscopic texture and the crystal structure of the metal near the surface.  After a part is treated, it can be dyed to give it color before it is sealed to increase durability. Hard anodizing is a similar procedure that penetrates further into the metal. This increases the surface hardness of the material making the surface even more durable and corrosion resistant.  It does not make the metal part stronger, it affects the durability of the surface of the metal.

Kashima coating is a type of hard anodizing that involves a lubricating treatment as well.  This not only substantially decreases friction, it also increases the hardness of the surface of the part, making it as much as three times more durable than chrome plating.  The process also increases the corrosion resistance 4-5x over normal anodizing.   Kashima coating is a process that is only done by one company in the world, Miyaki in Japan.  Fox ships all component parts to Japan where Miyaki treats them with the Kashima coating.  The parts are then sent back to Fox to be assembled.  

Currently Fox is the only bicycle company using Kashima coating.  It's a feature found on their Factory Series forks and rear shocks.  It increases the durability of the upper legs of a suspension fork and the shaft of rear shocks.  This makes them more scratch resistant than hard anodized finishes found on other shocks, including Fox's Performance Series.   It also gives them a lubricating property that decreases friction between upper legs/shaft and the seals.  The result is a very smooth feel to the suspension and exceptional durability.   

See the Kashima Coating website for more information about anodizing in general and technical specs on Kashima coating.  I encourage everyone to visit ridefox.com to see all Fox has to offer, including the updates to their 2021 product.

Please note: the above article is a simplification of a very complex process that (I hope) makes it easier to understand without getting overly technical.


*Kashima Coating is used in other industries, primarily in shocks for off road equipment, some machinery, and on pistons in some high performance automobiles.  Fox is the only company in the bike industry using Kashima coating on their products.

note: this is a re-post of an article that I wrote in 2015 on my other blog: thebikehive.blogspot.com