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Technical FAQ with Lennard Zinn: The limits of sealant

  • By Lennard Zinn
  • Published Dec. 7, 2010
  • Updated Feb. 23, 2011 at 12:41 PM EDT

Oops there goes another rubber tree plant. In this 2009 AFP photo, a Thai farmer collects latex after cutting a score across the bark of a rubber tree, at a farm in the southern province of Narathiwat.

Q. Dear Lennard,
Thanks so much for your excellent column. My question is about repairing cyclocross tubulars. I have a pair of new Tufo Flexus Primus 32 tubulars with a small 2-3 mm tear in the sidewall, which causes them to leak air down to about 15 psi, then hold. Since the tear three weeks ago, I’ve done three hard ‘cross workouts and had no problem with leaking air. The Stan’s in them appeared to do the trick, so much so that I raced last weekend on them, at which point they leaked air again down to about 15 psi during race (unrideable for me), where they held. Since then they are holding air fine. My dilemma is that they’re brand new and expensive, but obviously I need a reliable tire for racing. Can these be repaired?

Here’s a picture:

Dylan's torn TUFOHere's a picture.

— Dylan

A.Dear Dylan,
Sorry to say it, but that tire is done. Once the cords are cut, there’s nothing you can do to repair it. I hate it when that happens.

Also, sealant will be unreliable, as you’ve found, on a hole like that. The hole is on the side (sealant fills holes in the tread better, where it is thrown by the spinning of the tire). The hole will probably grow over time, and it’s already a big hole to fill.
— Lennard

Q.Dear Lennard,
Can products such as Vittoria Pit Stop be injected through a valve extender on a deep-section rim? Most tubular tires, as you are aware, have short valve stems, and on a deeper rim (40-50 mm) the prospect of removing the valve to inject a sealant (after mounting or for repair on the fly) really makes the direct injection the more attractive option.
— Brian
A.Dear Brian,

Vittoria engineer Samuele Bressan says:

“Our product Pit Stop Road Racing is of course possible to use through a valve extender, as it is with the valve core itself.
The only concern is to not allow the mechanism to become stuck together with latex, which could happen if someone is not familiar with the adaptor or does not completely empty the can; in that case, just a flush of air through the valve cleans out any residual latex. Easily done with any pump or CO2 cartridge.”

— Lennard

Q.Dear Lennard,
Count me as one who has not had success with Caffélatex. I had a small leak in a Vittoria Corsa road tubular. Small enough that it would take several hours to go too soft to ride it. I put in the Caffélatex and it initially closed the leak, but once I rode on it, it opened up and sprayed latex all over me and my bike. This happened during the state championship road race!

I refilled the tire several times with Caffélatex and it was never able to seal the small hole. I also couldn’t find any glass or thorn or other material stuck in the hole.

If it can’t fill a hole that small how will it work on a giant cyclocross hole?

Also, I couldn’t push the Caffélatex through my valve core like they said; I had to remove the valve.

I attempted to repair it by putting in more Caffélatex. I put in 30ml more, inflated to 120psi then stood back as latex shot out in a stream. I tried the Stan’s procedure of spinning/shaking the wheel to get some kind of foaming action going but it wouldn’t seal the puncture. So I put in 30ml more and repeated the procedure. This time it kind of sealed. A plug of latex formed on the outside of the puncture and latex continued to drip from around the plug for about 24 hours.

I have not had the chance to ride the wheel again since my road season is over. The tire now seems to hold air but I would not race with that tire again because I don’t trust that the puncture will stay closed.

When filling the tubular I screwed on the brass adapter/injector, then filled the injector then tried to inject the Caffélatex. This resulted in about half the Caffélatex going in the tire and the other half going all over the floor. On subsequent applications I removed the valve core.

I measured the puncture at about 1.5mm on the outside of the tire. I always run 110 to 120 psi in my tires, never more than 120.

I was going to run Caffélatex in my cyclocross tubulars this year but with the issues I had I didn’t see the benefit. Luckily I haven’t had a puncture yet this year.
— Jeff

A.
Dear Jeff,
Besides always running Caffélatex in my cyclocross tubulars, I have actually “cured” a Vittoria Corsa Evo CX road tubular that was losing an unacceptable amount of air on me due to a slow leak, but mine definitely had a very small hole. There was no hole visible on the outside of the tire. It must have been a very tiny thorn or something that came right back out.

I was intrigued recently when I read this marketing claim from Cantitoe Road, the U.S. distributor of Caffélatex:

Dugast, producer of some of the finest tubulars money can buy, are very concerned about latex inner tube/sealant interaction. Over the years they have received several warranty claims for tubulars where the tube had been cooked by the ammonia found in natural latex based sealants. Quoting from the test results they sent us after testing Caffélatex: “Racers have extensively field tested Caffélatex with our tubulars. The result is excellent, it’s the only sealant we recommend to our customers.”

I called Richard Nieuwhuis, the owner and director of Dugast, and asked him about this. He’s a busy guy, working 4 a.m to 5:30 p.m. six days a week, so I was pleased to get some time with him. His success on the world cyclocross circuit this season — with riders like Zdenek Stybar, Sven Nys, Katie Compton, the Cannondale-Cyclocrossworld team, Sanne van Paassen, and Marco Bianco winning numerous major races on his tires — has been astounding.

Nieuwhuis confirmed that the only sealant he recommends in his tubulars is indeed Caffélatex because, while it doesn’t fill large holes, it does stay liquid in the tire. He says that he is “not a fan” of Stan’s. He goes on to say, “Stan’s and other sealants with high ammonia content are good products, but after three to four weeks, the sealant starts to dry and is no longer a film.” He says that this destroys the latex inner tube.

Nieuwhuis is also quick to point out the limitations of Caffélatex and all sealants with a quality tubular like a Dugast. He says first of all that sealants won’t protect against snakebites (i.e., pinch flats) or big holes. He also points out that any sealant needs time to fill a hole, and that this is an issue with an inner tube, as opposed to a tubeless tire, whose inner diameter is always the same. The inner tube in a Dugast tubular (and indeed most tubulars and clinchers) is one-third smaller than the inside of the tire. Being elastic, the tube of course stretches more at a weak point (like where it has been punctured), which reduces the chances of the sealant working, especially when the rider starts riding right away again after adding Vittoria Pit Stop or other aerosol sealants.

Furthermore, Dugast offers the service of replacing the inner tube (we saw a method for doing that in this column some months ago) in a tire that has a perfect casing but has suffered a pinch flat. This costs 22 Euros, and the tire is good as new afterward, but not if sealant was used in the inner tube. “The sealant will get smashed around inside the casing, and the tire won’t be as comfortable to ride as it was before,” says Nieuwhuis.

Incidentally, Dugast does work hard on the issue of pinch flats. A latex tube is twice as resistant to a pinch flat as a butyl rubber tube, claims Nieuwhuis. But in a mountain-bike tubular, pinch flats are a much bigger problem, so he uses latex/silicone tubes in those, which are three times more resistant to a pinch flat as a latex tube, and six times more resistant than a butyl rubber tube. (A latex tube also costs three times as a butyl rubber tube, and a latex/silicone tube costs eight times as much as a butyl one.)

Finally, below is the response to your particular issue, Jeff, from the maker of Caffélatex.
— Lennard

From Caffélatex maker Effetto Mariposa:

I think that the conjunction of pressure, inner tube and damage size (1.5 mm) explains the sealant failure. Let me explain how I see it.

Sealants work at their best with tubeless systems, while their maximum-damage sealing properties are limited with tire-and-tube systems. It has to do with the way inner tubes deflate/move (a tube has no inherent strength; it just holds air and is much more flexible than a casing: the puncture hole geometry is changing constantly as pressure changes) and by the movements at the casing/tube interface (they are rubbing one against the other, tending to mechanically remove the patch).

Another limiting factor is high pressure: fixing a puncture at mountain bike or cyclocross pressures is easy; doing so at triple that pressure is a challenge for any sealant.

Caffélatex is widely used also for road tubeless applications, but in that case the pressure is slightly lower than standard road tires and the tubeless construction helps CL get the job done in case of puncture.

Not to excuse my product, but a 1.5mm cut on the tread (that could eventually translate into a bigger damage on the tube) at 110-120 psi on a tubular is a repair that is very difficult to achieve, not to mention holding the seal.

We’ve been reported of several cases of road tubulars where Caffélatex has been able to fix punctures while riding and in a final way, but they were more like thorns or 1mm-punctures at maximum. Above that, we’re entering a gray zone of sealant behavior at its functioning limits.

— Alberto De Gioannini
www.effettomariposa.com

Readers can send brief technical questions directly to Zinn.

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Technical writer Lennard Zinn is a frame builder (www.zinncycles.com), a former U.S. national team rider and author of numerous books on bikes and bike maintenance including the pair of successful maintenance guides “Zinn and the Art of Mountain Bike Maintenance” – now available also on DVD, and “Zinn and the Art of Road Bike Maintenance,” as well as “Zinn and the Art of Triathlon Bikes” and “Zinn’s Cycling Primer: Maintenance Tips and Skill Building for Cyclists.”Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and feeding and how we as riders can use them as comfortably and efficiently as possible. Zinn’s column appears here each Tuesday.

FILED UNDER: Bikes and Tech / Cyclocross / Technical FAQ TAGS: / / / / /

Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance and Zinn and the Art of Road Bike Maintenance, as well as Zinn and the Art of Triathlon Bikes and Zinn's Cycling Primer: Maintenance Tips and Skill Building for Cyclists. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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