Technical FAQ: Tubeless tire plugs

Have a question for Lennard? Please email him at veloqna@comcast.net to be included in Technical FAQ.

Dear Lennard,
I had a question concerning tubeless tires and flats. I am currently riding Roval Rapide CL50s, with Specialized 700x28s. Yesterday during a downhill, my front tire blew out, turning my frame and a good amount of myself into a sticky mess. I had a Dynaplug tubeless tire plug into it, which may have popped out, resulting in the explosion. So I suppose my question is twofold, and forgive me if you have covered this before and my first is redundant.

1. Is this a common/recurring problem with tubeless tires? I have had these tires for a few years now, and it has never happened to me before. Is this a sign of a needed replacement or any other technical problem that needs to be addressed? I did not lose the bead when the tire went.

2. What is your experience/knowledge of reliability with the Dynaplug tire plugs? I used another to plug the next hole, and it held for the remainder of my ride after I aired up the tire again.
—Luke

Dear Luke,
I have not seen a repair plug pop out of a tire, but I don’t have experience with them on road tires. A plug can come out if the puncture is larger than the repair plug and may have required more than one plug to make the seal.

Here is the official response I received from Dynaplug to your letter:

“Dynaplug is a road or trailside solution for emergency flat repair on tubeless tire systems. Repairs are good for the life of the tire, as long as a “good” or proper repair is made. A “good” repair may take multiple plugs based on the size of the hole, and the amount of sealant remaining in the tire.

Dynaplug repair plugs bond directly to the tire, sealing the puncture in real-time.

It appears that your reader got a second puncture, and was riding high pressure in his road tires. This would account for the sealant spray. The fact that the first repair plug was still in place indicates a second puncture was the problem. Multiple repair plugs can be used in a tire, sealing multiple punctures is not only acceptable but encouraged.
— Billy Sinkford, ECHOS Communications”

Here is a response from Challenge Tires North America:

“I have been running the Lezyne system [ed., a tire-plug system consisting of a reamer/insertion tool that pushes wire tire-plug strips into the tire] on my gravel bike and the Stan’s Darts [ed., a tire-plug system that works with the Stan’s sealant in the tire] on my mountain bike. And I am still running inner tubes on tires narrower than 32mm. I ran road tubeless back in the Hutchinson/Shimano era, and it was fine. But the inner tube system just works better for me on those common roadie sizes. I have found that narrower tires tend to lose a lot of pressure before the sealant begins to work, which requires me to still stop and inflate the tire. And if I am going to stop, I might as well spend some time examining the tire and maybe popping in a tube.

Back to your question and those from the reader: I am not familiar with any issues with Dynaplug or any other plugs in our TLR tires.

And the Dynaplug system seems to be very popular. Most of our supported gravel athletes are running that system and many of the riders around here (Madison, WI) do as well. I have seen these riders use the Dynaplugs thru both the tread and casing with great success.

I have seen plugs fail on road tires. I don’t remember the brand; however, these were similar experiences to what your reader mentions below. The first plug failed and the second was a success. We did perform some trimming on the second plug, and we assume that was the reason.

The first plug was jammed in the hole and left a bit of the “bacon” material — like an extended finger. We assume this finger was pulled out during riding considering the pressure between the road and the tire and there not being any knobs to protect it as with a gravel or mountain tire. We trimmed the bacon/finger on the second plug, and it stayed in place, with no issues. That rider checked his tire when he got home and did not find the plug inside the tire, so it was definitely pulled out, not pushed in.

In a second instance, I was on a gravel ride and a friend plugged his tire. It held just fine until we hit the pavement. Once we hit the pavement, the plug pulled out. We added a second plug, trimmed it, and that seemed to be fine on the road back to the car.

In both cases, the plug was placed in the center of the tread where the tire would be rolling on the pavement.

My assumption is that the extended plugs are being pulled from the tires when riding on the pavement. With two experiences where extended plugs are pulled out and trimmed plugs are not, that seems to support my theory. However, I have not performed any testing of my own to determine if this is the case.

In another experience, a friend plugged a tire and it held for a little while before we heard it hissing and saw sealant spraying from around the plug. We added a second plug and that seemed to fix the issue. In that case, the hole was bigger than the plug and the sealant did a good job filling that gap until we started riding. The flexing of the tire was causing the hole to open and close around the plug, and the sealant couldn’t compensate until we added the second plug. I had a similar experience to this with a truck tire as well. The first plug was not large enough, and the second plug was the solution.

I realize this doesn’t answer the question, but it might provide some potential causes.
— Chris Clinton, Challenge North America

From a tire engineer at Mavic:

I personally have experience with the Dynaplug plugs and I just love this kit: small, neat, anything you need in it, and super easy to use. I would recommend it to any cyclist using tubeless tires. The experience of your reader is concerning though.

Knowing that the metallic part of the plug stays inside the tire, I would tend to believe that it is impossible for it to pop out once installed. Unless the tire casing shreds larger, creating a larger hole and allowing the plug to pop out.
—Maxime Brunand, Mavic

From Schwalbe North America:

Yes, I have heard of a Dynaplug popping out, but am assuming it’s very rare. My educated guess is that it happens when the carcass has sustained a significant amount of structural damage (where with a tubed tire you’d definitely require a boot). A plug is excellent to get you home in a pinch, but my take is that any time a plug is required the tire is probably in quite a dubious shape.

My definition of when a plug IS required is when the sealant has been given the best opportunity to work and it has failed. These are the criteria I use:

1. The sealant is from a high-quality brand (only a couple of sealants on the market work well with tubeless road tires)

2. The sealant is in good condition and is less than 2 months old (unless it’s an ‘endurance’ formulation of some type).

3. The rider DOES NOT STOP if they notice the puncture (stopping is the worst thing that you can do).

4. Pressure drops so far that the bike is not practically rideable (usually 20psi or less).

5. The rider doesn’t make the mistake of trying to inflate the tire immediately once the sealant has done its trick (even if this is in the 20-30 psi range).

If sealant doesn’t work in the above conditions, then it’s a good chance the carcass has some fairly bad damage.
— Andrew Batchelar, Schwalbe North America

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Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder (www.zinncycles.com) and purveyor of non-custom huge bikes (bikeclydesdale.com), a former U.S. national team rider, co-author of “The Haywire Heart,” and author of many bicycle books including “Zinn and the Art of Road Bike Maintenance,” “DVD, 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 in physics from Colorado College.

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