Silca’s new Ultimate tubeless tire sealant is made of carbon fiber — really

Intriguing new tubeless sealant formula is claimed to seal a 5 mm gash at 100 psi.

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Silca’s eclectic range of products has grown yet again with the announcement today of its new Ultimate tubeless sealant formula. While the entry into the segment may be somewhat unexpected, what is wholly on-brand is that Silca Ultimate sealant incorporates some interesting tech features.

Ultimate is a natural latex-based solution, which the company claims to seal faster than synthetic formulas. Similar to Effetto Mariposa’s Caffelatex, it also includes a foaming agent that Silca says is better able to distribute sealant throughout the interior of the casing, as opposed to non-foaming liquids that reside more at the tire’s outermost circumference. 

Sounds pretty straightforward so far, right? The interesting part — well, one of them, anyway — is in the additives.

Sealant brands commonly use a diverse range of additives to help plug the holes (much like how platelets help create blood clots to seal cuts). Currently, all sorts of bits are in play, including glass and plastic beads, sand, glitter, fiberglass, and a variety of ground-up organic matter like pepper, walnut shells, and corn cobs. 

As for Silca? The new Ultimate stuff uses carbon fiber. For real.

Silca evaluated the different types of particle additives used by other sealant brands.

During the process of benchmarking competing products, Silca says that one consistent theme with additives is that the ones that had lower density, but more surface area, stayed more evenly distributed throughout the liquid instead of just being stuck to the center of the tread cap area. And yet despite some additives working better than others, Silca claims that in only the tiny minority of plugged holes did they actually find any additive particles at all; in almost all cases, the plugged hole is just liquid sealant.

Instead, Ultimate uses tiny bits of chopped-up carbon fibers that have also had all of its coatings and chemical treatments burned off — turning it into “pyrolized” carbon fiber. When combined with that foaming agent mentioned earlier, the claimed result is that Ultimate isn’t just everywhere inside the tire casing while riding, but is also better able to quickly plug holes because those pyrolized carbon fiber bits are evenly distributed throughout the liquid. 

According to Silca, the carbon-enhanced rubber plug created by its Ultimate sealant is far stronger and less likely to bust open later than plugs that were mostly just solidified latex.

How well does it work? Well, Silca says Ultimate will consistently seal 8 mm-long cuts in most low-pressure situations, 6 mm cuts at 80-90 psi, and holes as big as 5 mm at 100 psi. Notably, it’s those high-pressure claims that are most attention-grabbing since that’s where current sealants typically fall short. If Ultimate works as well as Silca says it does, that would indeed be pretty groundbreaking, and could go a long way toward increasing the acceptance of tubeless road setups.

But there’s a catch

There are some drawbacks to how well Ultimate seals, however.

Savvy readers might have already noticed that all of those hole sizes that Silca says Ultimate seals so well are bigger than the diameter of conventional tubeless valve stems. So why doesn’t Ultimate clog tubeless valves? Well, it does. Sort of.

Silca says it hasn’t found Ultimate to clog tubeless valves while in use, but it’s so good at plugging holes that it can’t be injected through tubeless valves like most sealants. In fact, it’s supposedly wholly incompatible with syringe-type injectors at all. Inconveniently, Ultimate has to be poured into the casing before the tire is fully mounted on the rim. 

But what about sealant longevity? And aren’t needle-type injectors also handy for checking the condition of older sealant that’s been inside the tire for a while? Yes, but Silca has addressed that, too.

The solvents used in latex sealants naturally evaporate over time, thus reducing their effectiveness. Traditionally, this is counteracted by just periodically adding more sealant, which wouldn’t be practical with Ultimate since you’d have to partially remove the tire. Instead, Silca is also offering a complementary product called Replenisher. This stuff is mostly just solvent, without any of the pyrolized carbon additives, and unlike the sealant, can be injected through the valve stem for easier maintenance. And since you still can’t easily check the condition of the sealant, Silca says registered Ultimate users can opt to receive email reminders to prompt users when it’s time to add Replenisher. 

According to Silca, the initial dose of Ultimate sealant will last up to 18 months (but more commonly around a year) when boosted with Replenisher as prescribed — roughly 1 oz per month, on average, depending on local conditions. Replenisher can also be added to lower the effective temperature range of Ultimate sealant, which can be handy for riders that don’t shy away from riding outdoors during the winter months. 

Ultimate has to be “boosted” every few months, but the long-term cost is supposedly lower than competing products.

As expected — this is Silca, after all — Ultimate and Replenisher do cost a bit more than competing products, at least upfront. However, Silca says that Ultimate and Replenisher customers will actually use less product overall than other sealant brands, and will spend less money — not more — over the long term. But also as we’ve now come to expect from Silca, neither Ultimate nor Replenisher uses any chemicals that are harmful to either people or the planet. According to Silca head Josh Poertner, the pyrolized carbon is nearly as innocuous as activated charcoal, and the main solvents in the sealant are water, some sort of synthetic alcohol, and food-grade propylene glycol (anti-freeze).

Ultimate sealant will be offered in 8, 16, 32 oz sizes, with respective retail prices of US$18, US$24, and US$38. The Replenisher costs US$12 for a 4 oz bottle. Pricing for other regions is still to be confirmed.

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