Technical FAQ: Tire sealants
In the past few months, we’ve discussed tire sealants a lot here. I thought I’d talk here about the ones that are available, as I get so many questions about them, and as we were unable to devote a section of the VeloNews Buyer’s Guide to them as planned. The Buyer’s Guide is now on newsstands, by the way, so check that out, too!
Tire sealants fall into two basic categories (although there is some overlap):
- a suspension of flakes and fine fibers in a liquid, or
- a natural or synthetic liquid rubber (i.e., latex).
They all take advantage of escaping air, the tire’s rotation throwing them to the outside, and gravity to stop air leaks. One type stuffs the hole closed with fibers and particles; the fibers wrap around the chips and form a plug. The other type closes the hole off with solid rubber that solidifies as compressed air passes over the liquid rubber as it escapes through the hole. Some sealants contain ammonia or other chemicals that can damage rims over time.
Most of the fiber/chip sealants contain a mixture of water, a water-miscible carrying agent such as propylene glycol, and the bits and pieces that will fill the hole. These can be paper fibers, synthetic fibers, mica flakes, polyethylene chips, hydrated bentonite clay, and all manner of other items that will clog a hole. A sealant need not have the glycol; it could be completely water-based, but it would tend to separate and freeze at temperatures often encountered while riding and could dry out quickly.
Sealants can be poured into a tubeless tire when mounting it, or they can be injected through the valve of a tube or tubeless tire. Injecting through the valve is best done by first removing the valve core to avoid clogging the valve. Latex-based sealants can be injected through Presta valves with non-removable valve cores, but fiber/flake-based ones cannot (you can remove the end nut with pliers and allow the valve pin to drop down into the tube, but you have to pinch the tire or tube with your fingers to hold the pin below the valve or you’ll lose it during injection or removal of sealant).
Given enough time, most sealants cease to be active and should be cleaned out; if they solidify, they unbalance the tire with useless weight concentrated in a single spot. Removal is easy to do on a tubeless tire by removing the tire; the fiber-based sealants can be wiped out and rinsed out with water, and the latex-based ones can be rinsed or peeled out once solidified. On a tire with an inner tube, including a tubular, you’ll need to remove the sealant through the valve, which requires removing the valve core, and ideally rinsing and sucking it out.
If a sealant is used in a tube tire that subsequently gets a puncture, you must remove the penetrating object or it will flex in the tire, continually un-sealing the hole and shredding the tube.
Stan’s NoTubes: The original liquid latex-based sealant on the bicycle scene that made it possible to run non-tubeless tires as tubeless, Stan’s seals well up to quite large punctures. Stan’s offers a syringe injector as well as rim-sealing tape and rim strips to run non-tubeless rims as tubeless.
Effetto Mariposa’s Caffélatex: A foaming synthetic latex-based liquid sealant containing no ammonia. The foaming action created by the tire’s movement is intended to seal sidewall and rim-side punctures, while most sealants, thrown outward by centrifugal force or pulled down by gravity when stationary, only seal the tread side. Available with rim-sealing tape and syringe injector.
Vittoria/Geax Pit Stop: Two different brands for the same product, this is an aerosol containing a foaming latex-based sealant. Via its flexible tube, inject it through the Presta valve with the valve core in place to seal/inflate a new tire or to seal a tire that has received a puncture.
Hutchinson Fast’Air: Fast’Air is an aerosol containing a foaming latex-based sealant. Via its flexible tube, inject it through the Presta valve with the valve core in place to seal/inflate a new tire or to seal a tire that has received a puncture.
Schwalbe Doc Blue: A liquid latex-based sealant in a squeeze bottle, you can pour it into the tire on mounting or inject it through the valve with a syringe.
DT Swiss Tubeless Kit: A liquid latex-based sealant in a squeeze bottle, you can pour it into the tire on mounting or inject it through the valve with a syringe. Seems to solidify in the tire in normal use more rapidly than other latex-based sealants.
Slime Pro: Consisting of fibers and chips in a glycol-based solution, Slime was the biggest-selling bike-tire sealant before latex-based sealants came along. Now, Slime Pro combines a latex-based sealant combined with a fiber/chip sealant to plug holes as well as to seal tire beads more like a latex-based sealant.
There are many other fiber/flake sealants on the market available for use in bicycle tires.
In a practical application of sealant (specifically Stan’s) use, here is a sampling of the instructive mail I got following my November 11 column, which discussed tubeless ’cross tires and sealants.
It was interesting reading about your reader’s problems with tubeless ’cross tires.
I have been riding two seasons now on tubeless clincher cross tires from NoTubes. These are the Raven tires you can find on their Web site. I have had no flats and not problems. Wheels are bulletproof Neuvation M28 Aero.
I believe a key element is the cross rim strip supplied by NoTubes. It takes up space under the tire bead to keep it from moving around under the edge of the rim and burping. I run around 28-30 psi most of the time.
My team receives some small sponsorship from NoTubes. Their building is just down the street from where I live.
This might be a help to Greg, who’s trying to run tubeless for ’cross racing.
I have a Salsa ’cross bike set up with Hutchinson Piranhas, tubeless, with Stan’s cyclocross rimstrips and sealant. When I got them my shop, Cayuga Cyclery in Ithaca (which has a close working relationship with Stan), told me they will burp at low pressure if I use the yellow tape rim strips (the standard set-up for road).
The ’cross rim strips have the valve and rim strip unit as one piece, and the black strips (butyl, I’m guessing) are softer than the yellow tape … the softer material fills my rim cavities (I have Easton Vistas) below the bead hook and there is no burping. I lost pressure one day on a ride, down to 15 psi, I’m guessing, and I rode it home without a burp, even though I had to be careful not to bottom out on the rim. I don’t race, and keep my pressure to 50-60 psi because I take paved roads to get to the dirt.
In a recent column, you describe how Hutchinson tubeless CX tires “burp” at low pressure. The solution to this is to run a Stan’s No Tubes conversion rim strip. I’ve been running both the Bulldogs and the Piranhas on Ksyrium SL wheels with the Stan’s cyclocross rim strips. I can get them to seal on those rims without (those strips), but they burp badly.
With the Stan’s rim strips, I regularly run 25 psi with no burping and I weigh 170. Any less pressure for me and they tend to fold in corners, but never burp. My wife runs the same setup at 19-22psi! I think it is also important to use a good sealant and make sure a bunch of it gets up on the inside of the tire bead interface by shaking the wheel and laying it on its side for a couple minutes. Repeat for the other side, then repeat for both sides several times.
I’m not sure you could fit the Stan’s cyclocross rim strips in a Shimano tubeless rim, but in a regular rim, they tend to fill the space under the tire bead, keeping them from burping. Stan’s makes a CX-specific version, but I have also stretched one made for a 26-inch MTB rim onto a 700c wheel with good luck. It starts out wider than your standard road rim, but when you stretch it out, it gets just narrow enough.
Overall I find I still prefer a good supple tubular like a Dugast (barely), but for the price difference, lack of pinch flatting, and ease of mounting the Hutchinson tubeless is hard to pass up. It totally sucks when your $120 Dugast suddenly becomes useless.
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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. Readers can send brief technical questions directly to Zinn. Zinn’s column appears here each Tuesday.