Latex Tubes - A Case Study -- Part 1

Unit's picture

As a bit of background, I will tell you why I started this little jaunt into expensive tubes. I have a set of wheels that are tubular tire specific and recently was forced to ride them for a month or so. I immediately asked myself why I do not ride them more often because they rode so nicely. When I say nicely, I mean that they stick to the road like glue, they roll like a clincher with 140 pounds per square inch (PSI), but they feel like riding on clinchers with 70 PSI (that is to say very soft and supple).

I do not want to stray on the topic of tubular vs. clincher. Keeping things simple, I will simplify and say that I attribute a large part of the difference (tubular vs. clincher) to tire casing quality and use of a latex bladder inside to keep air in (for most high quality tubulars). I can buy some pretty awesome quality clincher tires and narrow or eliminate the advantage between casings, but this study will focus on the other aspect (tubes).

For the purposes of this little study I will use the latest and supposedly greatest offering from Michelin (the Pro Race 3 Service Course). Yes, I know that many will point out that this is perhaps not the “awesome casing” that I alluded to earlier, but it is a casing that has worked well for me. It may not be nearly as supple as an “open” casing clincher, but it has performed much better than open casings have for me in that it lasts longer for my style of riding which does not include a lot of racing.

For those who are not familiar with the terminology, an “open” casing is one that has many if not all the qualities of a tubular casing except that it is left open and beads are installed for use as a clincher. Open casings carry a premium price and are optimized for racing and generally not well optimized for high mileage. The dollar per miles associated with open casings outweighs my priority for ride quality. I am interested in exploring if a 10-15 dollar increase in tubes will give me a economical improvement in ride quality.

So, for the purposes of my “study” all testing will be done on Michelin Pro Race 3 Service Course (PR3) tires. All noted differences will therefore be limited to what this tire constrains.

Cost differential:
Butyl tubes have increased in price remarkably over the past year. I will not get too deep into why, but it has to do with raw material prices, oil prices (which effect shipping cost), and the U.S. Dollar compared to the currencies in foreign markets where all tubes are produced. Yes, at this time, no bike tubes are manufactured in the United States.

I recall buying Kenda Butyl tubes for $1.99 each. A major online bike shop now list the least expensive butyl tubes for $5.99 and Latex tubes for $11.99.

Simple math shows us that twelve bucks is the financial penalty for trying latex tubes. Not really that bad if there is an improvement…especially if the improvement puts a larger-than-$12 smile on the rider’s face. That is going to be tough to gage though.

On the Work Bench:
I will assume you have handled a butyl tube, so I will skip the description.

A latex tube is different in almost every way. First the color is a light green to aqua blue, and the tube has a generous coating of powder (perhaps talc). Secondly, the tube is very limp, not unlike an unrolled condom or a cooked noodle. The latex tube also has much greater elasticity in that you can easily stretch it and it springs back to its original shape (butyl will return but does so much more slowly). In a poor attempt to describe what I am talking about; If I were to try to fire a butyl tube like a rubber band it would probably go a third of the distance that a latex tube would go.

Another observation is the lack of seams in a latex tube. These things appear to be one continuous extrusion of latex tube that is joined near the valve (you can see this union in the photo). Perhaps this lack of seams and mold lines (that are always evident on butyl tubes) results in a more uniform texture that in turn allows the tire/tube system to behave more uniformly. I should point out that no tire is truly uniform either....they all have ply splices where continuous sheets of fabric must be joined together. However it seems logical that greater uniformity is better for reduction of rolling resistance.

Installation:
Both latex and butyl tubes install about the same way. I would suggest using a generous coating of talc powder for either tube. Talc reduces friction between the tire casing and tube, this will allow for greater ride comfort. The friction reduction offered by talc also allows the tube to move around and distribute itself better during the initial inflation (if this does not happen, a tube can pinch, tear, and/or cause the bead to unseat catastrophically).

The latex tube, because of its wet noodle-ness was a little trickier to install (it almost "flows" as it falls out of the casing as you try to install it). If you need to change a flat on the roadside, butyl tubes will likely be a bit easier and therefore faster to install. I am not sure how happy a latex tube would be in a saddle bag or jersey pocket, but I have no reason to believe that it would have a shorter shelf life than a butyl tube as long as both are stored in a dry, dark, and cool place.

Anecdotal info: I have seen a demonstration where a tech places a business card between the tube and casing (lawn mower tire) and used the tire assembly for a week under normal conditions. After the week the tire was dis-mounted and the business card was partially shredded demonstrating the unexpected movement between a tube and casing. I have also observed tubes that were stuck to the casing as if vulcanized in place, while this may not be a bad thing, I can only assume that preventing motion between two components of the structure will result in more rigid structure…which is really what I want to avoid here.

Short Term:
Rumor has it that on a road bicycle tire (700c) latex tubes loose air faster than butyl tubes. Most normal butyl tubes I have used loose between 2 and 5 PSI from an inflation pressure of 100 PSI in a 24 hour period of time. In other words about a 2-5% decrease in daily pressure. Latex is said to be about double this, or 5-10% change in daily pressure. It has a lot to do with the thickness of the tube, generally a thicker tube will be heavier, but will loose air more slowly.

For the purposes of this test, I define “short term” as duration consistent with 50% or more of my ride durations. In 3 hours time there was no perceptible bleed down of air pressure. My gage is only sensitive to a change of 2 PSI, and my butt certainly can not discern a couple PSI after 3 hours in the saddle.

More Anecdotal Information: All air is not equal. Atmospheric air is about 78% nitrogen with most of the balance being oxygen. Both of those molecules are diatomic meaning that two atoms are present in every molecule (so the smallest particle of air we encounter most of the time is the size of two nitrogen (N) atoms, or two oxygen (O) atoms).

Who cares? Well, N2 is “bigger” than O2 with respect to permeability, so if you could inflate with pure nitrogen you will loose air slower. However, over time you will achieve a higher concentration of N2 in your tires as the O2 (and other) constituents preferentially bleed off and you replenish your tires to 100 PSI each day.

I do not want to get to far from home here with valence shells and bond shapes, but let’s just say that there is a really good explanation for why a tire filled with a CO2 inflator will not hold pressure nearly as long as one filled with pure Nitrogen. Should you go out and pay for a fill up of pure nitrogen? Heck no! You will get nearly pure N2 in a few weeks time from daily replenishment of your tires with a standard floor pump for free!

I bring this up so that readers will understand the difficulty of comparing tubes based on pressure bleed rates*. A tire installed and filled months ago will actually bleed pressure 1% slower than one installed and filled today due to this nitrogen fractionation. Further, heed the advice of purging CO2 from your tires when you get home after an emergency roadside fill up. YOu should re-inflate a CO2 filled tire with a floor pump for best and most economical results.

* some riders state that their latex tubes bleed fast but they may be comparing a newly installed latex to a butyl that was on the bike for months prior (and therefore had a very heavy nitrogen fraction compared to the 78% nitrogen in the recent fill).

I will post a second part of this when I can give more long term observations. I hope to report on the ride qualities if they can be perceived. I hope to report nothing else, but as with many performance items there is a trade off somewhere, so I will report any I encounter. Yes, I am approaching this with hopes, but this approach is hardly *scientific* anyway.

I will however also share some scientific data that has been collected by others in this second installment. Racers tend to like any edge they can buy, and this may be a relatively cheap way to reduce rolling resistance. Stay tuned!

Click here for part 2.

Unit's picture

Short term report

Unit wrote 5 years 34 weeks ago

I have been playing with latex now for a few days and several miles. I have but a few observations to share thus far.

The pressure loss over a 24 hour time span can not be ignored. Every day I inflate my tires to 115 PSI before I ride, and by the next day's ride, the pressure is down to 95 PSI.

I have no way to quantify this, but there is a distinct shock absorbing quality to this set up. I feel bumps of course, but the sharp "edges" of the bumps are greatly diminished, and the "buzz" of chip and seal is slightly muted. It seems to have an effect similar to lowering the operating pressure of the tires, and while the tires are losing air faster than with butyl tubes, the loss during the ride is not sufficient to describe the feeling.

I have really come to appreciate this set up in the curves. I find that I can really lean into the tire and carve the apex a lot harder and with far more confidence.

It could all be in my head, but even if it is...I am diggin' it.