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Silca Ultimate Tubeless Sealant delivers something that not all sealants can - the ability to cope with the high pressures used in road tyres. It works quickly and effectively, blocking holes before much air escapes so you shouldn't need to pump at the side of the road.
Over the past few years, I've tried all kinds of sealants in a lot of tyre and wheel combinations, and thankfully the majority have been very good. Probably the only thing that lets quite a few down is their inability to be able to cope with higher road pressures. Many are fine up until 50psi to 60psi, but above that the sealant can keep blowing out.
I tend to run my tyres at around 90-100psi for 25mm or 28mm and, if I'm honest, I find punctures rare - purely because very few things can force their way in. But if you do want to run tubeless at those pressures, I highly recommend this Silca stuff.
As expected, I didn't puncture throughout the test period so with various household items (drawing pins, nails, scalpel blades and so on) I cut through a test tyre. I found the Silca Ultimate fixed holes up to around 6mm - the company claims 7.5mm, but that's dependant on the width of the slash.
The largest I made was 6mm long with the scalpel blade and 0.5mm wide. The sealant bubbled up and had it sealed within about 30 seconds. Not much air escaped either - starting off at 100psi, it only dropped to 85psi.
Pumping more air back in, I found the sealant could cope with just under 95psi on the gauge before it started to leak again.
It works, according to Silca, by using a foaming latex that carries a mixed blend of 6mm, 9mm and 12mm carbon fibre strands. The latex bubbles up, forcing the carbon fibre strands to block the hole.
Silca recommends pouring it directly into the tyre before popping it onto the rim, as its fast-drying formula will start to activate if you syringe it in through the valve, apparently. After all, it can seal holes bigger than your valve.
To be honest, I always empty the contents into the tyre before fitting, rather than going for the valve option anyway. The Silca Ultimate has been in my tyres now for around six weeks and is showing no signs of drying up yet, which to be fair is expected.
Silca recommends using its 4oz Replenisher (£12) after three months to give the Ultimate sealant a top up, so I'll be checking on it in about six weeks time to see how much is still liquid. Then I'll test the Replenisher.
This bottle I'm testing here contains 473ml (16oz) of sealant at a cost of £24, which works out at just over £50 per litre. If you are using it on road tyres up to 30mm, this should be enough to fill eight tyres; alternatively, it's enough for about five gravel tyres of 30-45mm.
A lot of the sealant I get sent to test is in much smaller containers of around 100ml-250ml, so that affects price comparisons, like for like.
The CST Tubeless Tyre Sealant is £10 for 250ml, so £40 per litre. A good chunk cheaper, but it didn't work so well on bigger cuts.
Muc-Off's No Puncture Hassle Tubeless Sealant can be bought in a litre bottle for £29.99. I was impressed with it, but you definitely need to buy it in bulk for it to be cost effective.
Silca Ultimate is a very impressive sealant, and it copes well with the high pressures used in road tyres. It's not that extreme price-wise either - at least not when buying in this larger container.
Works very well on high pressures, and quickly too
If you're thinking of buying this product using a cashback deal why not use the road.cc Top Cashback page and get some top cashback while helping to support your favourite independent cycling website
road.cc test report
Make and model: Silca Ultimate Tubeless Sealant 16oz
Size tested: 473ml
Tell us what the product is for and who it's aimed at. What do the manufacturers say about it? How does that compare to your own feelings about it?
Silca says, "SILCA Ultimate Tubeless Sealant uses the power of a foaming latex formula combined with chopped carbon fibers to boost sealing power even at higher pressures. Ultimate Tubeless Sealant contains 5% by volume, 6, 9, and 12mm chopped carbon fibers which have been reclaimed from recycled bicycles, carbon wheels, racecars, and aircraft components. A unique foaming latex formula allows for the very lightweight carbon fibers to be evenly dispersed within the sealant while riding, which allows for a higher fiber content than possible with Kevlar or fiberglass. At this high fiber loading, bundles of carbon fiber are carried directly to the puncture by the sealant flow where thousands of micro-bubbles collapse on each other, depositing their high stiffness carbon fibers over the hole. During this process, the carbon fibers form a dam of fibers against the tire casing not unlike a beaver dam of sticks blocking the flow of a stream. This dam of high stiffness/high strength fibers has been shown to seal holes in testing up to 7.5mm, some 25% larger than conventional technologies.
After the puncture is sealed, that area of the tire is left with a zone of carbon fiber reinforced latex bridging the top and bottom of the hole, helping to reduce the likelihood of future punctures in that area when compared to other sealant additives such as cornmeal, glitter, or fiberglass.
This superior sealing ability and hole reinforcing ability of the carbon fiber also allows for a higher concentration of anti-freeze agents in the sealant which means more effective sealing at low temperatures (6mm holes seal at 18deg F/ -7deg C), as well as longer lasting sealant (7-9months depending on humidity)."
It's a high quality sealant that'll work quickly on high pressures as well as low ones.
Tell us some more about the technical aspects of the product?
* Effective down to 10F/ -12C
* Seals 7.5mm holes for up to 6mo
* Must be poured into tire during install
* Not injector compatible (It seals holes bigger than
* Use Replenisher every 90-120 days for best
* 6, 9, and 12mm recycled carbon fibers are dispersed evenly by a foaming latex to create ultra strong seals
* Made in the USA
Tell us how the product performed overall when used for its designed purpose
It works quickly and seals large holes in high pressure tyres.
Tell us what you particularly liked about the product
Seals at high pressures, and quickly.
Tell us what you particularly disliked about the product
How does the price compare to that of similar products in the market, including ones recently tested on road.cc?
It's not the cheapest out there, but it's still entirely competitive.
Did you enjoy using the product? Yes
Would you consider buying the product? Yes
Would you recommend the product to a friend? Yes
Use this box to explain your overall score
This is an impressive sealant that'll work on a range of tyres and pressures. It's not the cheapest, but worth it for the peace of mind.
About the tester
I usually ride: This month's test bike My best bike is: B'Twin Ultra CF draped in the latest bling test components
I've been riding for: Over 20 years I ride: Every day I would class myself as: Expert
I regularly do the following types of riding: time trialling, commuting, club rides, sportives, fixed/singlespeed,
With 20 years of road cycling and over 150,000 miles in his legs it's safe to say Stu is happiest when on the bike whatever the weather. Since writing his first review for road.cc back in 2009 he has also had a career in engineering including 3D-CAD design and product development, so has a real passion for all of the latest technology coming through in the industry but is also a sucker for a classic steel frame, skinny tyres, rim brakes and a damn good paintjob.
His fascination with gravel bikes is getting out of control too!