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Technical FAQ: Sealing snakebite flats, replacing Exalith pads and converting threaded stems

  • By Lennard Zinn
  • Published Sep. 18, 2012

Editor’s Note: Lennard Zinn’s regular column is devoted to addressing readers’ technical questions about bikes, their care and how we as riders can use them as comfortably and efficiently as possible. Readers can send brief technical questions directly to Zinn.

Dear Lennard,
Is it possible to use sealant to seal a hole in an inner tube or tubular tire on the rim side? I’ve followed your recommendation and have used sealant in my clinchers’ inner tubes and in my tubulars on my CX bike, but I’ve had a few pinch flats, and the sealant doesn’t take care of that.
— Jared

Dear Jared,
Good news! Yes, there is! Here is the rig I used to seal a pinch flat I got in a cyclocross race on a virtually brand new Vittoria EVO XN tubular tire. The tire was so new, I couldn’t stand to give up on it, but I sure didn’t want to open it up and patch it, either. Some 30 years ago when I had the time and motivation to do so, I would patch tubulars on long drives to races. But if you’ve done it, you know what a pain it is, and you also know how you can never get the base tape glued back down over the stitching as it was when new. I just couldn’t stand to downgrade this beautiful new tire like that, nor can I carve out time for things like that these days.

As you undoubtedly know, or you wouldn’t have asked the question, sealant is great for filling holes on the outward-facing side of the inner tube and tire. You can simply pump up the tire with sealant in the inner tube, and rotate the hole to the bottom and let it sit. It may take a few inflations and addition of more sealant, but unless the hole is simply too big, it will eventually seal. On this particular tire, air was just gushing out the outward-facing hole, right through a hole in the tread caused by hitting a sharp rock. Being a Vittoria tire, it has a valve stub on the inner tube, and the valve screws onto it. I unscrewed the entire red valve (see photos) and screwed on a long, upside-down valve Challenge valve extender so I could inject sealant into the tire without removing it from the (deep) rim. I pushed a piece of plastic hose onto the upward-pointing skinny end of the valve extender and pushed a syringe body onto the tube. Then I poured Stan’s NoTubes sealant into that. I chose Stan’s, because in the May 2010 issue of VeloNews magazine, I did a sealant test on cyclocross clinchers with inner tubes in them and Stan’s sealed the biggest holes. On the other hand, a few years ago, Dugast recommended only using Caffélatex sealant in Dugast tubulars and specifically against Stan’s sealant, saying that it could burn the inner tubes. Well, given that this tire was going to be junk if I didn’t get this to work, and knowing that the hole to the outside was huge, I chose Stan’s. There have been too many times that I’ve tried to seal big gusher holes with other sealants and have just ended up with white liquid all over my garage floor and still had a flat tire. So I’m willing to risk the inner tube scorching if I can get some more life out of this tire.

In that 2010 sealant test in VeloNews, I also theorized that riding and bouncing around on the tire might seal the rim-side hole or that perhaps the foaming action of Caffélatex would allow it to fill the rim-side hole of a snake-bite pair of holes from a pinch flat, but no dice on either count. That’s why, when I first answered your question directly, I said that there is no way to seal the rim-side hole in an inner tube with sealant other than by completely filling the tube with sealant. But now I know differently.

Here’s the method:

Clamp the deflated tire (which has sealant in it), rim down, onto a narrow object right at the puncture hole, and then inflate the tire. I did this by using a cam strap and strapping the wheel down to a drive-side crankarm — something narrow enough to clamp up into the tire yet with a platform (the spider arms) that the wheel will stand on vertically. Then I pumped the tire up. The tire was clamped down so tightly that the tire could not inflate fully at the bottom. That way, the sealant, which had flowed down to the holes, was up against the hole in the roof of the tube as well as the floor of the tube there. And it filled that rim-side hole in the roof of the tube immediately!

Previously, it had spewed sealant out of the large hole to the outside (in the floor of the tube, since I had the hole at the bottom so the sealant would cover it), and while the rate of spewing had slowed, it hadn’t yet sealed that hole; it needed more sealant. So I took the valve out again, put the upside-down valve extender back on the valve stub on the inner tube, and injected more Stan’s sealant with the syringe. But once that hole in the floor of the tube (clearly the much bigger of the two holes forming the snakebite pair) had sealed, air was still bleeding out through the sidewalls of the tire all of the way around. I could see this by smearing soapsuds on the sidewalls. However, once I strapped the wheel down so that the inner tube could not expand where that hole was and had to keep it wetted with sealant, the hole sealed right up!

This sure beats the heck out of either patching or throwing away a good tubular! I’m sure this will also work with a standard inner tube in a clincher, but it’s probably simpler to just patch or replace the inner tube.
― Lennard

Dear Lennard,
I’m from Surabaya, Indonesia…
I just bought a new Mavic Cosmic Carbone SLE wheelset and there is
Exalith brake pad comes up with. Is it ok if I replace the Exalith
brake pad from Mavic (SwissStop) with Dura-Ace brake pad, or other
SwissStop product? There is no Mavic distributor in Indonesia,
so I can’t find the Mavic Exalith brake pad.
Maybe my question only can be answered by Mr. Zack from Mavic…
— Dita

Dear Dita,
This is the answer from Mavic PR/tech guy (and former VeloNews tech editor) Zack Vestal:

He’ll be fine to use Shimano Dura-Ace pads for as long as necessary. They’ll wear a little faster than the green Exalith pads, but they work just fine. In fact I’ve been testing them and they’re actually quieter than the green pads, so far.

― Lennard

Lennard,
I have a 1989 Waterford-built Schwinn Paramount. It is the pride and joy in my stable of bikes.

About 10 years ago, I decided it needed a carbon fork. Now I’m thinking of going retro a bit on it by re-installing the steel fork along with my old Campy Delta brakes.

Question: If I reinstall the fork (1-inch, and threads), can I use the Ritchey WCS stem I used on my Ouzo Pro, clamping safely over the threads or should I bust out my old Dura-Ace quill stem or find a new stem?
— Brent

Dear Brent,
Wow. That would never have occurred to me to do. With a threadless headset, you mean? First off, unless you had a bunch of spacers stacked into your threaded headset when you were running that fork, there won’t be enough length of steerer sticking up to clamp your stem to. Secondly, it was never meant to be used that way, and the stress riser created at the bottom edge of the stem where the thread has cut through over half the thickness of the steering tube would greatly increase the chances of the steerer snapping right off at the bottom edge of the stem. I sure would never try this. Go back to your quill stem.
― Lennard

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Lennard Zinn

Lennard Zinn

Our longtime technical writer joined VeloNews in 1987. He is also a framebuilder, a former U.S. National Team rider, and author of many bicycle books, including Zinn and the Art of Mountain Bike Maintenance 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. He holds a Bachelor’s degree in physics from Colorado College. Readers can send brief technical questions to Ask LZ.

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