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Technical FAQ with Lennard Zinn: That slow leak

  • By Lennard Zinn
  • Published Apr. 13, 2011
  • Updated Jun. 26, 2011 at 4:52 PM EST

Q. Dear Lennard,
So earlier this week, I upgraded to road tubeless using an Ultegra wheelset and a pair of Fusion 3s. I inflated the back tire using a CO2 cartridge, and the front I had to take to a bike shop so they could fill it with their compressor (the mechanics gave me a look when I said “road tubeless” and told me I was suicidal, but filled my tire anyway).

So now, my front tire is great, but my rear wheel keeps losing most of its air overnight. I think the bead is seated correctly, because I can pump it up with a hand pump. And I can ride an hour on it just fine, and it still feels hard when I get back. It just won’t hold air overnight. (And yes, I have sealant in there, Effetto Mariposa Espresso).

I can’t figure this one out. What could be the matter? And is it even safe to be riding it?
— JL

A. Dear JL,
Yes, the bead is probably now seated correctly if you can pump it with a hand pump. Cover the tire and rim with soapsuds and inflate the tire. See where the air is coming out, and rotate and tilt the wheel appropriately so that the place where air is bubbling out is at the bottom so the CaffeLatex can go there and plug the hole. That will fix your problem unless the rim is leaking.

If air is bleeding out of the rim around the spoke nipples, the seal on your valve stem is leaking. It probably simply needs a bit of sealant, but it could also be a bad valve stem. Remove the valve stem, put some CaffeLatex around the rubber seal at its base, and put it back in. That has fixed every one I’ve ever had leakage there with, other than on rims that had gotten corroded around the valve hole by a corrosive tire sealant. Only hand-tighten the valve-stem-retaining nut; you want to be able to remove the valve stem without tools should you need to install a spare inner tube on the road.

I suspect that it’s simply the time frame that makes it seem like it’s behaving differently when sitting than when riding. I’ll bet it leaks while you ride, too, and if you were to ride all night long, it would be as soft in the morning as when you leave it sitting inflated overnight.

Assuming you’re using current tubeless-compatible Ultegra wheels and those Fusion 3s say “tubeless” on them (I don’t know why Hutchinson uses the same model names for tubeless and non-tubeless tires…), then yes, it should be safe to ride on. The beadlock of the road tubeless tire with a tubeless-compatible road rim is very good and generally keeps a deflated tire on the rim better than a deflated standard clincher stays on.

One thing to keep in mind is that road tubeless tires are folded tightly in the packaging, leaving kinks in the bead at many places around the rim that tend to not seal along the rim shelf. For a tire that won’t seal, simply put a tube in it and ride it for a while. It will take the proper shape soon enough. Then take the tube out, wet the beads, put in the tubeless valve stem and a couple tablespoons of CaffeLatex sealant, and pump it back up. It may not even require an air compressor or a CO2 cartridge to seat the bead, once it’s been ridden a while.

As to your interaction at the shop, I absolutely cannot understand why so many bike shop employees try to discourage customers from using road tubeless tires. I’m convinced it is simply because they have not used them successfully themselves. I think that indicates rather poor shop training on the part of road tubeless tire and wheel makers and a lack of interest in keeping up with what is current on the part of the shop personnel.

I was super irritated when one of my Bay Area customers ran into roadblocks like this with his own local bike shop. He has Fulcrum 2-Way Fit (meaning they are tubeless-compatible as well as compatible with a standard clincher and tube—characteristics shared by all road tubeless wheels) wheels and Hutchinson Fusion 2 Road Tubeless tires on a bike we built for him. He wanted to replace his worn tires and wanted a shop to do it for him. Thinking ahead more than most customers would, he looked on the Fulcrum website for Fulcrum-authorized retailers in his area and went to one of them.

An employee there started right off telling him how he thought road tubeless tires suck and recommended against using them. But at 6-foot-8 and 245 pounds, this customer is prone to flat tires and wanted the same reliability he’d gotten used to. I think the shop didn’t even have any road tubeless tires in stock and had to order some in, requiring a second trip for the customer. Finally, the shop went ahead and slapped on a pair of road tubeless Hutchinsons without wetting the beads and without using sealant inside (Hutchinson even sells its road tubeless sealant by the gallon with a twist spout — couldn’t be easier for a shop to use it!).

My customer managed to get all of about eight miles down the road on his first ride before one tire went flat and he ended up calling me. I spent some time on the phone bringing him up to speed on how to do it himself. The bummer is that he’s a busy executive who would rather not spend his time working on his bike and would like to leave that to somebody else. Now he understands the system and can educate the bike shop employees who stand in his way on how to use a simple system that they should already know. I’m still shaking my head at how an “authorized retailer” of a wheel brand that makes road tubeless wheels does not understand how to use them.

I ride Hutchinson tubeless tires on all (three) of my road bikes and never have bleed-down issues unless I haven’t ridden one of them in months. (I also ride tubeless tires on my mountain bikes, and often on my cyclocross bikes.) On bikes that don’t get much use and hence don’t run through tires during the course of a season, I do replace the sealant at least annually.

Besides providing a very nice ride with good grip and lower rolling resistance due to the ability to run lower pressures without fear of pinch flats, road tubeless tires have completely eliminated flat tires for me. I simply do not get flats anymore on my road bikes, and I’m a big guy. One of the things that was a pain for me when doing all of that testing of carbon clincher wheels for VeloNews (you did read that test in the magazine, didn’t you?) was that I couldn’t use road tubeless tires in them. I was constantly having to fix flats out on the road, since we have a lot of sharp stuff on the roads here in the wintertime. There are few things I dislike more than changing road tires in cold weather.

I have discovered that if I wear through the tread to the point that I can see the casing, a road tubeless tire no longer holds air. And once, I hit a sharp rock at high speed that cut my rear sidewall, requiring, of course, installing a tube and a boot to get home and then replacing the tire. This would have destroyed any tire, but it was cool to see that the tire stayed on despite the high speed and curvy descent. Wanting to see what it would do, I rode the rest of the way down the mountain—over a kilometer, and the tire stayed on until the final switchback, when one bead finally came off.

I only wish that road tubeless tires were offered in larger diameters and road tubeless wheels were offered in bomb-proof models. I have many customers who are near or over 300 pounds and who climb in very low gears. High rider weight combined with lots of torque due to pedaling a low gear with lots of leg power can snap spokes in short order on the available tubeless wheels. And while Stan’s NoTubes makes a road tubeless rim strip that would seal up any road rim, including on bomber wheelsets we build here for customers like that, I’m a bit leery from a liability perspective about selling tubeless tires with rims not specifically made for that application. I also am more comfortable philosophically with having the little beadlock ridges that road tubeless wheels have on the inboard edges of the bead shelves to lock and seal the bead.

The (un-stretchable) carbon fiber bead on a road tubeless tire is square, rather than having rounded corners, and it snaps into the square shape of a road tubeless rim’s bead hook and is further retained by the hump. Stan’s rims have a lower bead hook specifically for tubeless use, but his rims are known for being lightweight, not for being ideal for 300-pound riders. So, rather than sending a 300-pound guy out on road tubeless tires on wheels not made for it, I just tell him that he’s simply going to be dealing with frequent flat tires unless he uses super heavy-duty tires and tubes that ride like a truck. It’s a real shame to not be able to offer riders like this the rolling and cornering performance, comfort, and freedom from punctures and pinch flats that road tubeless tires offer.

I’ll get off of my soapbox now. JL, if you get those tires and rims sealed properly with that CaffeLatex (same stuff I use, BTW) and don’t continue to ride them after the tread is completely off, you can expect great performance and flat-free riding with them. Don’t give up, and don’t listen to bike shop employees who try to convince you to not use them!
— Lennard

Re: Regarding overpronation:
Dear Lennard,
An orthotic is a device that controls excessive foot motion during ambulation. Locking the rear foot in place with a varus post will prevent the mid tarsal joints from unlocking and pronating. Bicycling is not a true weight-bearing sport, and the foot does not go through its gait cycle. The only place to control the foot on the pedal is in the forefoot, hence the varus wedges.

The other way to control the amount of rear foot motion on the bike might be to make sure the seat is adjusted at the higher point of the acceptable range therefore limiting ankle dorsiflexion. After that, our anatomy is what it is, some things just cannot be changed. Some are sprinters, some can go the distance, some can hit a 100 mph ball, some can’t. Sometimes if you try to change the dynamics of the foot on the bike, you affect the knee.
— Alan Shier, DPM
Podiatric Medicine & Surgery

Re: Dear Lennard,
Just thought I would add my two cents.

This scenario is fairly common. In addition to a varus forefoot being common this person may also have a slightly higher Q angle.

Maybe a slightly more narrow hip, but the solution is most often a simple one.
— Paul Swift
Founder, Product Development, BikeFit.com
www.bikefitpro.blogspot.com


Follow Lennard on Twitter at www.twitter.com/lennardzinn

FILED UNDER: Bikes and Tech / Technical FAQ TAGS: / / /

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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