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I've been using CST Tubeless Tyre Sealant for an extended test period, and it has been working well, plugging smaller holes quickly and showing no signs of drying out even with the very hot weather we've had. And though it hasn't lived up to the big 7mm holes claim, it does come very close.
Most tubeless sealants are claimed as being able to fix holes from around 3mm up to 5mm, but CST reckons its offering can seal up to 7mm diameter holes.
To test this, I pierced one of my gravel tyres with the point of a flat wood 32mm drill bit, leaving a hole of around 2mm in width and 6.5mm in length to see just how good the CST sealant was at dealing with what would be quite a severe gash out on the trails. It didn't fully seal it, though it did give it a very good go.
The 40mm tyre was pumped to 40psi before piercing, and the sealant started to block the hole quickly, with very little in the way of pressure loss. Although it didn't seal the hole completely, it did slow down air loss, allowing me to keep riding for about 20 minutes before the tyre was flat. This might give you enough time to get home, or at least get somewhere flat or dry away from the road or track to fix it.
On smaller, more typical holes you'd get from glass, thorns, sharp stones and the like, I found the CST sealant to be very good. Installation is simple, too, thanks to the nozzle easily fitting inside the valve core, so you don't end up with any mess.
Using an old tubeless road tyre that had previously been fitted with an inner tube, I was amazed at how many small nicks and cuts were on it. The sealant quickly showed itself and sealed all of these small holes – and they have remained sealed even after a few hundred miles.
It copes well with higher road pressures without blowing out, too.
We've had some very hot conditions during the test period, and after a couple of months of use, removing the tyre showed the sealant to still be very much a liquid, with no sign of any of it 'balling' in certain areas of the tyre.
CST recommends topping it up every six months, or three months if you live in hot climes.
At £10 for 250ml (£4 per 100ml) it's not priced too badly; it's a cheaper option than Muc-Off's No Puncture Hassle sealant at £8.99 for a 140ml sachet (£6.42 per 100ml).
When it comes to quantities used, that ranges from 30-50ml for up to a 32mm road tyre, 50-80ml for a 700C gravel tyre, up to 140ml for a downhill mountain bike tyre, so for most of us roadies you're going to be looking at around five tyres' worth of sealant.
Overall, although I couldn't quite get the largest hole to seal, the CST made a pretty good effort, and for the more typically sized punctures you are likely to pick up I'd say it's a sealant you can rely on.
Works on the majority of holes, and though it doesn't quite hit its claims it’s still impressive
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road.cc test report
Make and model: CST Tubeless Tyre Sealant
Size tested: 250ml
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?
CST says, "CST tubeless tyre sealant has been engineered to seal holes of up to a whopping 7mm in diameter, ensuring riders can continue to ride on some of the most hazardous surfaces with full confidence that they can still cycle home. Formulated to spread evenly throughout the inside of the whole tyre, the sealant's anti-ball formula ensures even, perfect coverage for continued smooth riding, minimal rolling resistance, and all-round puncture protection.
In addition, CST's Tyre Sealant is made in the UK, supporting the UK economy and reducing CST's carbon footprint."
It's a good sealant that'll work on various tyre types and pressures.
Tell us some more about the technical aspects of the product?
Clings to the whole inner tyre
700c 23-32mm - 30-50ml
700c 32-50mm - 50-80ml
26" up to 2.5" - 80ml
27.5" up to 2.5" - 100ml
29" up to 2.5" - 120ml
Downhill up to 2.5" - 140ml
Tell us how the product performed overall when used for its designed purpose
It didn't match the claims on the bottle, but does a good job on the majority of holes.
Tell us what you particularly liked about the product
It's well priced and worked well on typical sized punctures.
Tell us what you particularly disliked about the product
It didn't work on the largest hole I tried.
How does the price compare to that of similar products in the market, including ones recently tested on road.cc?
It's more cost effective than many when it comes to buying it in small packages like this, some by a big margin, as you can see from the review.
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
A decent sealant for the majority of punctures and sealing jobs, though it didn't hit its 7mm hole claim in testing.
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!