Michelin Aircomp Latex Presta Tube
This year, it was time again to try out the latex.
Latex isn't just for fetish wear anymore. Latex, aka natural rubber aka original rubber, is the stuff, sap, which comes out of that rubber tree plant. Latex bicycle tubes are rare and coveted. One of the few companies importing tubes to the US is Michelin. We procured some tubes and set out to see how they rode. We had high hopes for this latex test. The first bicycle tube was made from it by gluing two strips of latex rubber together; then it was wrapped in linen tape and glued to a tricycle wheel (Dunlop was cushioning his son's trike), making the first tubular tire. The rubber most of us know and use on a daily basis is butyl rubber, aka synthetic rubber, which was developed in 1937 by Standard Oil and became the standard rubber used for most applications thanks to the Japanese military blocking the Asian rubber trade before and during World War II.
Butyl tubes have some advantages over latex. Butyl is more durable. It's less expensive. It holds air better. It can be easier to patch.
Latex tubes have a few advantages over butyl. They should ride better. They should be harder to flat. They produce less rolling resistance.
It is hard to fathom that something less durable is harder to flat. But the two are really different criteria. Durability refers to a whole host of factors. Flatting to a single. The reason latex should both ride better and be more flat resistant is that latex tubes are thinner and the material more flexible. Yes, this makes a difference even when pumped up with 120lbs of tire pressure.
A related example that should explain the above phenomenon: Not all tires are built the same. Some have more threads per inch (tpi) than others. Think of a Conti' Gatorskin compared to a Veloflex Record clincher. The tires with the higher tpi invariably feel faster when riding, and tests show they are faster. The higher tpi tires have thinner casings, are more flexible, and harder to flat. The cost is that the tires generally don't last as long because the casing is easier to cut and there's less tread.
We had heard that latex tubes were faster pretty much since we started looking into tubulars. High performance sew-ups often come with latex tubes. The lore was that the latex helped contribute to the performance advantage tubulars enjoyed. When we got around to our first round with latex tubes, the experiment ended early and poorly. We picked up three Air-B tubes at a swap meet. Crazy light, supposedly weighed 45-50g apiece. They came covered in talcum powder and sealed in a plastic bag. That was in the fall. In the spring, we took them out of the plastic bag and put them inside brand-new open tubulars. Flatted both over the course of two rides. Split lengthwise, along a seam that didn't exist.
A few years later, Pariba latex tubes came to us inside light Pariba tires on a set of training wheels. These fared better, though both were finished in a month, thanks to sharp gravel cutting the casing of the Paribas.
Spending the kind of time we do poring over data, we decided it was time to revisit latex tubes. The particular piece of information that pushed us over the edge was the tire test that Bike Tech Review (BTR) has published and revised over the past several years. The tests were performed by a BTR member who says, “I'm just a retired engineer with too much time on his hands.” Al Morrison has done us all a great favor. He devised a testing protocol and ran it for lots of tires and tubes, comparing tires to tires, tubes to tubes, glue to glue, and pressure to pressure. In particular, he found that in lab conditions (a smooth roller, wheels with 100lbs of downward force, tires pumped to 120psi, and spinning at 51kph), latex tubes could save .7-2.8watts of rolling resistance per wheel. Morrison attributes the differences to the tire. Remember these are lab conditions. 200lbs of person and bike pedaling on two PVC rollers at 51kph in the lab should experience latex resulting in a reduction of rolling resistance from 1.4-5.6w. Rolling resistance should be higher on the road, and thus the savings greater. The cost of rolling resistance on the road could be 50w or more for a 200-pound person. Latex tubes can reduce that cost by 10-20%.
Some costs are hard to bear. People don't wear a skinsuit every ride, nor do they wear an aero helmet or run a rear disc. Comfort, practicality, safety, handling are some of the reasons people don't do those things. Latex tubes look like a winner in the lab, but we didn't know how they'd fare on the road. If they were like either of our first two attempts, latex wouldn't be worth switching.
Our first task was weighing the tubes. We took four tubes, two short valve and two long. We removed the plastic valve caps and the plastic sleeves over the valves. We're told the latter prevents oxidation and should be removed before installing tubes. All weighed between 85-88g. This is considerably more than the 75g advertised. When we consulted Michelin, they told us the 23mm tubes with 36mm stems should weigh 80g with a variation of plus 15% and minus 10%. The 23mm tubes with 60mm stems should weigh 82g with the same variation. The 20mm tubes should weigh 70g with the same variation.
The tubes are green because Michelin added green dye to the mix. Without dye, they should be a milky white. The tubes are seamed right next to the valve. This is to give some extra supporting material for the valve. As we've read stories of latex tubes failing at the valve, this makes good sense.
Measuring and observing completed, we pulled out our old tubes and put talcum powder inside the tires. We've never seen proof that talc really helps prevent the tube from pinching, but since we'd rather not flat, we figured the less than 1g of cure wouldn't adversely affect anything. Tubes went in easy. We installed them in both training wheels and race wheels.
We pumped up the tires and rode. We didn't notice the tubes making a performance difference, but that doesn't mean the saving isn't there. Our big mistake is we started testing a number of products at once, all of which could have the effect of making us a bit faster. Usually, we install one new product at a time to see if we can isolate the difference. But even in ideal conditions, saving even 5w would be hard to measure on the road.
After a month of daily riding, we've had no problems with the tubes. The bike is stored in a space that stays between 65-72 Fahrenheit. We rode daily but checked tire pressure every other day. We pump the tires to 110psi and two days later, our pressure gauge usually reads between 70-80psi. The race wheels are down to 30psi after sitting unused for a week.
The one thing we haven't tested out with the tubes is patching. Michelin says their latex tubes can be patched with a standard patch kit.
At this point, we might as well try. We've developed a fetish.