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Tech FAQ: Flat tire causes, tubeless tire failures and more

Lots of interesting tire talk in this latest edition of Tech FAQ with Lennard Zinn

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Flat tires, tubeless tires, and more

Dear Lennard,
It is a widely held belief that glass on the road causes flat tires. I have had my share of flats and often find the cause. I usually find metal or thorns and have never found a piece of glass! Has anyone one done a scientific study (i.e., intentionally riding over broken glass in a controlled situation) to prove that glass is indeed a significant risk for flatting a tire?
— Doug

Dear Doug,
I asked this question of Jan-Niklas Jünger, bike-tire product manager for Continental, and this is what he had to say:

We did a lot of studies with our RevoSealant to understand the cause of flats. Mainly holes are caused by thorns, and cuts are usually caused by pieces of metal or sharp stones. Glass can also cause cuts, but glass doesn’t have a single sharp edge like with a metal piece, and it breaks down into smaller pieces if you run over it.
Jan-Niklas Jünger
Product Management Bicycle Tires
Continental Tire Division

I personally have gotten flats on road tires where the culprit was a tiny piece of glass that I dug out of the tire tread that had worked its way through the tread strip, the puncture-protective strip, and the casing. I imagine this took quite a bit of riding to work its way through.

In the case of tiny whitish-clear chunks I’ve dug out of tires, I’m also unsure that I could definitively distinguish a shard of clear glass that had broken down to a tiny fragment from a tiny piece of quartz broken off from a rock.

I have also cut my finger on glass when wiping my tire immediately after riding through the remnants of bottles shattered on the road. It’s nowhere near as bad as the gash in my finger I once received when wiping off my tire when a sharp piece of metal got lodged in my tire. While certainly the latter would have punctured my tire sooner, I’m certain that the former would have eventually done so as well.
― Lennard

Dear Lennard,
I have question about tubeless tires. Why doesn’t anyone try to inflate their tubeless tire set up with nitrogen or argon? Possibly meaning the sealant would be less reactive and the gas would stay liquid until you have a leak. So, you wouldn’t have dried sealant and bugger buildup. The other advantage in cold temperatures (I live in Alaska and bike at really cold temperatures) is the stable psi.

Dear Adam,
Well, I suspect it is simply the reason that stops most of us, namely that it would be expensive and a PITA to inflate our tires with argon or nitrogen compared to just pumping them up with ambient air.
― Lennard

Dear Lennard,
I was reading your recent post and wanted to share another story with you about tubeless. I was out for an enjoyable two gap ride with some friends. We had just climbed the first gap of the day, Lincoln Gap, and were descending at about 35mph when out of nowhere my front tire let out a big bang. Before I could even respond I was down on the pavement. Luckily, I stayed on the road (there’s a steep ravine) and my wounds were limited to a significant amount of road rash.

I was running Specialized 2bliss tires mounted on Giant SLR-1 tubeless compatible wheels (w/rim strip). I’ve ridden tubeless for probably 10,000 miles on road and had no issues until this blow out. The blow out had the tire completely come off the rim and jam up my front wheel.

Days later when I was repairing the bike at home, I found that I was able to remount the tire on the rim and it held air. The tire did not get a hole or have the bead blow out. I was worried because the tire did not ‘fail.’

Some people speculated that the tire got over-pressured because of heat generated on the wheel by braking action. But we had only been descending for two minutes, and the rim was not hot to the touch. What do you think could have caused this blow out?

Dear Chip,
I don’t know. It makes logical sense that it must have experienced a big increase in pressure in order to blow a tire off that had otherwise remained safely mounted.
― Lennard

Dear Lennard,
Living in NM, I love tubeless on the road because goathead flats are thing of the past. As long as you’re using a little sealant in them. I do also like the ride.

The biggest downside I’m finding is nobody makes a good high mileage training tire. There’s no Continental Gatorskin or Michelin Pro 4 type tire out there. I’m finding there’s a paradigm shift in expectations. People I talk to think if they get close to 1,500 miles on a rear tire and about double that on the front it is good. This is in line with the mileage I get – on average 1,250 miles for a rear tire. It seems I’m changing a tire every 6 – 8 weeks! This is in line with my expectation for a non-tubeless Conti GP 4000. Which is basically a race tire. Whereas, with Gatorskins or Michelin Pro 4 Endurance, I typically got 3,000 miles on the rear tire. I also find the casing durability is not much better on tubeless than on GP 4000 and nowhere comparable to a Gatorskin.

What will it take to get tire manufacturers to put out a good, durable, high mileage tubeless training tire?

I’ve tried a most of the Hutchinson line, Intensive (1 and 2), Sector, Fusion 5 performance, and Schwalbe Pro One. At this point I’ve decided to stick with the Pro One only because I can get a great team price on them.

Dear Mike,
Though I assume your question is a rhetorical one, I’ll answer it anyway. I believe it will take people like you demanding them.
― Lennard

Dear Lennard,
Regarding a reader’s question in your last post about road tubeless failures, he mentions that he was riding Hed Ardennes rims. Hed clearly states that the original Ardennes are not safe to run tubeless; only the wider Plus rims are. If he isn’t running the newer Plus rims, he should avoid running tubeless. The Plus rims have a more standard tubeless bead shelf that really locks the tire in.

Dear Lennard,
I read with much concern the letter last post about a reader’s bad experiences with road tubeless. I’m running road tubeless on my bike and my wife’s bike. I’m using Roval wheels, but my wife is on Hed Ardennes wheels like your reader. We very rarely get flats and have never had a burp or sudden loss of air. We’re both using Hutchinson Sector 28’s.

But I was so concerned about his experience with tubeless and Hed wheels, I did a little additional research. My wife’s wheels are Hed Ardennes Plus, and while they do have spoke holes and rim tape, they are marketed as “tubeless compatible.” I’m curious if your reader’s wheels are Ardennes Plus or the previous standard Ardennes.

I will say that while the Sectors mount up relatively easily, they can be a pain to get off the Hed Ardennes. The bead of the Sector is so firmly ensconced in the rim bead it is very, very difficult to get it free. Perhaps, though, that is a good problem to have.

Since I’ve also been an early adopter of road tubeless and been through several years of a love/hate relationship I’ll say that Hutchinson has finally got it right with the Sector 28’s. Even so, I’ve been wanting to try the Conti tubeless, since Continental tires have always been high quality. But, reading about those issues I guess I better wait until the new Conti tubeless is proven safe.

I do have one question for you. The PSI recommendation on the side of the Sector says minimum 87 PSI and max PSI of 101. We both run about 60 PSI and I’m surprised that Hutchinson would say the minimum is 87 PSI. Any thoughts on this discrepancy?

Dear Edward,
I don’t know. I tried all of the contacts I had at Hutchinson and received no response back. That is a surprisingly high pressure range for a tire of that size.
― Lennard

Lennard Zinn, our longtime technical writer, joined VeloNews in 1987. He is also a custom frame builder ( and purveyor of non-custom huge bikes (, 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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