What type of inner tube holds air the best?

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Whenever I have scheduled an early morning ride, I usually inflate my tires the day before and call it right. However, this can put a little too much confidence in the ability of the tire system to hold pressure. Have you ever thought about the rate of air loss and whether it may be enough to impact your commute?

This question led me to do some quick tests on a few popular tube types to see how much pressure drops when there is no mechanical leak or flat. And while I’m sure the results won’t surprise much, there’s no denying that some types of tubes require more attention than others.

Permeation explained

All bicycle tire systems suffer from permeation, a phenomenon that occurs when molecules of a gas diffuse through the materials that contain them. However, not all containing materials are created equal, and some certainly allow more permeation than others. Compared to a car’s tire system, bicycle tire systems often need to be softer and lighter, and in turn, permeation is a much more important factor in cycling.

“Some people think the wastage rate increases on rougher surfaces, but we have never conclusively demonstrated this,” said Silca owner and professional team technical consultant Josh Poertner. “It is essential to remember that the mechanism here is not exactly mechanical, it is represented by gas molecules escaping through the pores of the tube, but it is actually a problem of solubility when the gases dissolve in the rubber, then travel through the rubber and out to the other side.

The point of my little test isn’t to give exact numbers to one type of tube – my sample size is just too small and your results will vary depending on the exact products you have. However, my test repeatedly revealed trends that I have experienced and heard from others over the years.

To test this, I configured four wheels with the same model and tire size, all with the same internal rim design, same internal rim width, and same rim tape.

Four wheels with internal rim profiles, rim tape and matching tires were used for this test. Unfortunately, I did not have access to more control wheels to expand the scope of this test.

While there are specialized tools for measuring permeation, my method was simply to focus on the pressure loss. For this I used an EVT Bleed’n gauge because the valve design allows me to reliably put it on the valve without significant pressure loss (i.e. no audible air loss) and she is not at all hungry for the air she takes on board. In repeated testing it always showed a difference of less than 1 psi in connecting, removing and reconnecting the gauge – good enough for this test.

Three main tube materials

This simple test was designed to measure a small number of common tube materials that are popular in road cycling. For this I tested a new Maxxis Welterweight like the regular butyl rubber tube, a Vittoria Latex tube, a regular Tubolito (TPU construction), then the Tubolito S (super light TPU construction) *. In a separate test, I measured a Specialized Turbo lightweight butyl tube against the same Vittoria Latex and Tubolito S as above, over a 24 hour period.

All tires / chambers were pumped to 80 psi and left for 24 hours at room temperature. Here are the first results measured:

  • Tubolito S: 79 psi
  • Tubolito: 79 psi
  • Latex Vittoria: 73 psi
  • Maxxis welterweight (normal weight butyl): 77 psi

The tires were then left for an additional six days to measure the loss over a period of one week:

  • Tubolito S: 72 psi
  • Tubolito: 76 psi
  • Latex Vittoria: 53 psi
  • Maxxis welterweight (normal weight butyl): 73 psi

As noted, the separate test involving the Specialized Turbo tube was only performed for a 24 hour period (using the same pressure gauge, wheels, and tires as above). The pressures after 24 hours were:

  • Latex Vittoria: 73 psi
  • Tubolito S: 79 psi
  • Specialized turbo (light butyl): 75 psi

From this we can see that the full weight Tubolito, a tube made from TPU, is the most effective at retaining air. The lightweight version of Tubolito and regular butyl tubing are not far behind, while lightweight butyl and to a greater extent latex suffers from significant permeation.

Unsurprisingly, thicker tubes of the same material hold air better than thinner (lighter) tubes. Keep in mind that this is not a statistically valid test and that even identical tube models can have differences in air retention.

“Historically, latex tubes [lose] around 1% per hour, but modern additives like graphene typically reduce them to less than 0.5% per hour, ”Poertner said. “Of course it’s variable, so there will be some differences between the ‘identical’ tubes, but in general, if you have a six hour event and the pressures have started at 90 psi, and the mechanics have inflated tires ~ 1 hour before start you probably end up at 84 psi.

What about tubeless?

Trying to find permeation trends in tubeless systems is a bit like trying to explain failures to a cat: it won’t happen.

Even assuming the tubeless system is completely devoid of physical leaks, there are simply too many variables in the tire construction, rim tape, rim design, and sealant used. And even more than inner tubes, tubeless tires from an identical manufacturing batch can exhibit significant differences in porosity.

Generally speaking, a well-configured tubeless system can offer comparable air retention to a regular butyl tubing – it should still be usable after a week. Some brands are pushing the boundaries of their tire construction and relying entirely on liquid sealants to create a system that retains air. Meanwhile, other brands, such as Goodyear and Giant (whose tires are made by Maxxis) have outfitted their tubeless tires to provide superior air retention – and I can attest to that making a sizable difference.

Some tubeless systems are quite effective at retaining pressure. For example, Cadex tires manufactured by Maxxis provide air retention comparable to that of a regular butyl tube.

For example, a few years ago, Giant switched all of their performance bikes, regardless of discipline, to tubeless. Part of that move was to create a tubeless tire system that would stay inflated in a workshop for a decent amount of time without using tire sealant (which can dry before the bike is sold). While this generally works as expected, such a feature isn’t just uncompromising and tires that generally offer the least permeation also tend to be a bit heavier and in some known cases run slower.

Permeation planning

Suppose you have an epic race or an endurance race coming up, what can the penetration rate tell us and how do we predict it? Well, this is a subject that Poertner is all too familiar with, and while permeation is a factor, it must be considered in light of the weather forecast, road conditions, rider power and the structure of the lane. ‘event itself.

“The process that we lead with our teams is to look at what we consider to be the critical point of the race,” he said. “We then factor in the loss / time x hours between that time and getting the bike ready, and then we look at the weather to see if we are further adjusting the temperature variations between those same times. ”

Poertner’s advice is often to err on the low side of pressure for most surfaces, especially if there is rain in the forecast. However, for an event like Paris-Roubaix, this advice is usually reversed, and it’s about finding the lowest pressure without the risk of breaking the wheels, and then tweaking it slightly from there.

“For an event like Roubaix, we are testing the tires and noting the loss rate on the sidewall because it is so important to get it right on race day,” he said. “You also have two completely different surfaces that can have an optimum pressure difference between them of 25 psi, so we have to choose which direction to optimize for. [It’s] not an easy question.

“The spring classics are also great in that you can have quite large temperature variations, so an hour before departure the temperatures can be quite cold. In 2019, we saw temperatures rise by almost 30 ° F (around 18 ° C) throughout the run, an increase of about 3 psi over the course of the day, which directly offsets your loss from permeability.

There are also alternative gases that permeate more slowly or are less responsive to temperature changes. “Nitrogen is cheap and common, although you will still have losses,” Poertner said. “None of [alternative gasses] really sort it out.

So where does all of this leave us? There are certainly trends in the way the different types of tubing maintain pressure. Simply put, those using ultralight latex and butyl tubing will need to monitor pressure loss more closely compared to those using regular butyl or fancy TPU tubing. However, it is important to remember that even identical models of tubeless tires and tubes can vary in terms of air retention efficiency.

Before a big event, it is worth determining the approximate permeability of your selected tube or tubeless system and assessing if this is something you need to factor into your starting pressures.

* Note that the characteristic image shows different tubes than those used in the test. The characteristic image shows a Continental Race butyl rubber tube (far right) and a Michelin latex tube (second from right).

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