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Technical FAQ: Questions on tubeless tires

  • By Lennard Zinn
  • Published Jul. 23, 2013
  • Updated Oct. 30, 2014 at 5:28 PM EST
This week, Lennard Zinn answers reader questions on tubeless tires.Material is added near the spoke holes for added strength. Photo: Caley Fretz | VeloNews.com

With more riders adopting road tubeless wheels and cyclocross season just around the corner, we’ve seen a number of questions related to tubeless set-up come in lately. This week, we’ll touch on bent-rim repair and sealant issues, and print one reader’s step-by-step tips for installing tubeless tires.

How much dent is too much dent?

Dear Lennard,
I recently dented the front rim on my Shimano Ultegra 6700 tubeless wheelset. It was a small dent, less than one centimeter long with less than one millimeter of total inward deflection. I carefully straightened the rim, and it is only slightly noticeable when braking. The wheel is true. I’ve set up Hutchinson tubeless tires on it again. They mounted easily (thanks to your previous post) and ride well, but I’m wondering if there’s any danger in continuing to ride a tubeless rim that has been dented and then straightened. Could the rim fail catastrophically? Could the tire blow off?
—David

Dear David,
If it’s a small dent, I think you have no cause for concern. Obviously, if the wear indicators on the brake track indicate that the rim is worn out, you have to be concerned about rim failure. But on a good-condition rim with a small dent like you describe, I don’t think you need to be concerned. I’ve ridden for years with no problems after fixing dents of that magnitude on road tubeless rims, and after straightening much bigger ones on MTB tubeless rims.

By the way, the Morningstar Rim ’Rench is the proper tool for fixing that dent.
―Lennard

Sealant in my valve stems?

Dear Lennard,
I’ve seen in your Technical FAQ column where you’ve recommended using sealant (and Caffelatex, in particular) for tubulars and tubeless tires. Since I’ve started using Caffelatex in my tubulars, I haven’t had a flat. However, one thing I’ve found with this product is that, due to its foamy nature, it will actually plug my valve stem/stem extender to the point where I can’t pump any air in without poking out the plug with a straightened paper clip. I use Schwalbe tubulars with removable cores, so I know Caffelatex is plugging the stem, not the valve core. Has this been your experience as well? If not, I wonder why I’m seeing this behavior. Too much Caffelatex in there (though I’m using the volume Effetto Mariposa recommends for road bikes)?

Also, the foaming nature of Caffelatex would seem to address another point you’ve made about sealant, where you say sealant doesn’t work for snakebite punctures on the rim side. If Caffelatex is sealing my valve stem, it seems it would work just as well on that type of puncture.
—Brett

Dear Brett,
The sealant is not filling your valve stem or valve extender because it is foaming and moves into that area when the tire is spinning. Rather, I think it gets in there because when you let air out, you’re not being careful that there is no sealant in the valve, and when air comes out, so does sealant, under pressure, so it dries and fills the area.

Before you inflate or deflate your tire, leave the wheel to sit for a while with the valve at either the 5 o’clock or 7 o’clock position. This allows the sealant to drain out of the valve, and it is away from the pool of sealant that is sitting at the bottom (at 6 o’clock).

I did a test for the print edition of VeloNews a number of years ago to see if any sealants filled holes on the rim side due to foaming or other action, and none do. So it won’t go into the valve while riding.
―Lennard

Fulcrum Racing 1 for cyclocross?

Dear Lennard,
I have ended up with two sets of Fulcrum Racing 1 2-Way Fit wheelsets. Instead of selling one set, I want to get your thought on using them for ’cross this fall? I have used other wheels (not dedicated 2-Way Fit) and have experienced burping problems running a tubeless setup. Do you think the Fulcrums will hold up to the rigors of ’cross?
—Scott

Dear Scott,
I’ve used those rims tubeless for cyclocross and never had a burp. So did my daughter. And the wheels are still holding up fine.
―Lennard

Tubeless tire installation instructions

Dear Lennard,
I have never seen a step-by-step breakdown on how to mount a tubeless tire to the rim, despite so many people having a heap of trouble. Please share this because I feel it will smooth things over fall many readers:

1) Clean all sealant gunk from rim and tire combo. You may want to remove your valve stem and inspect at the same time. It can’t hurt;
2) Reassemble valve stem into wheel per manufacturer specs. Don’t forget rubber o-rings from Mavic and Shimano if that is your system;
3) Start working one side of the tire onto the rim. Having everything clean and dry will pay off here. It will be easier to grip with your hands. Sealant is a slimy mess, no pun intended. Make sure the bead is falling down into the center channel. Here is the key: mount the section by the valve stem last. (Think about that lump the valve causes in the center channel. The valve causes the bead to be tighter (no different than tightening your belt, then trying to tuck your fist into the waistband of your pants; the bead is designed to fit the rim, not the rim and valve lump). If you mount the last five-to-eight inches by the valve last, you are not dealing with the extra tightness caused by valve.);
4) With one side mounted, prepare your sealant of choice;
5) Begin mounting the second bead. When you get to the last five-to-eight inches, dump the sealant in through the not-yet-mounted section of tire by having the valve stem at 6 o’clock position (remember you mount the valve area last);
6) Rotate valve up to 12 o’clock position (now sealant isn’t where you are trying to mount the tire); and
7) Pop the last few inches of tire on, with much less struggle by not fighting extra tightness caused by the valve.

This is great for wheels that use tape — Stan’s, Enve, or many other converted tubeless. By not using levers you are much less likely to muck up the tape by forcing a plastic tool down into the rim bed area.

As far as a pump to mount these without a compressor, I recommend Topeak’s mountain pump. Retail is fairly cheap; any shop can order it from their distributor, QBP. I just mounted some Bontrager road tires to Dura-Ace rims last night.

This should be possible to mere mortals. To put things into perspective, I am the size of the Schleck brothers (6-foot-2 and 145 pounds). I have a lot of luck. So don’t think this is just a trick for men nicknamed “The Gorilla,” like André Greipel.

Maybe this will make the web and help people get their tires mounted and flats behind them.
—Matt

Dear Matt,
Thanks. I particularly like your pants waistband analogy to describe what I was talking about in this column from July 2.
―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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