Graphics and narrative by: A.V. Schmit
Wheels and tires, wheels and tires, wheels and tires… Seems like on every ride that’s all people can talk about these days. So, I thought it might be of value for the 303 Endurance community to write a primer about the evolution of bicycle wheel / tire design.
While it usually makes sense to start most stories from the beginning. I think in this case, it makes more sense to start in the middle, as I would anticipate many readers have never ridden on a tubular tire shod hoop.
Until the advent of tubeless road wheels, the dominant standard was the clincher wheel. That consisted of a rim with a “hook” that turned inward toward the center of the wheel, and a tire that had a “bead” reinforced with wire, or in the case of foldable tires, reinforced with Kevlar or other aramid fibers like Vectran.
When a tube is inserted into the tire and mounted on the rim and inflated, the tube presses the bead into the hook of the rim. It is that pressure that holds tire onto the rim. This is what most riders use and have likely ever used.
Now, let’s take a step back. Originally, tires and tubes for road bikes were a single unit. You may have heard the term “sew up” in the US or “single” in the UK and Australia. They both refer to a tubular tire.
Essentially, a butyl or latex tube is contained within the casing, usually made from cotton fabric that has the tread bonded to it. Then the casing is sewn together with an additional strip of fabric glued over the seam.
The rim, which has a shallow concave channel, is prepared with a number of layers of specialty tubular adhesive and the interior of the casing of the tire is also coated with a number of additional applications of the same adhesive. Then the tire is stretched over the rim and carefully centered over the channel and left to cure.
Now, if you are thinking, “what a hassle.” You’d be right, gluing up tubular tires under the best of circumstances is a bit of a smelly mess.
The advantages of tubular tires are they tend to be more supple and lighter than clinchers and can be ridden in an emergency when flat. The disadvantage is a puncture by the side of the road is a most unpleasant experience, even if you have an extra tire with you.
Which is why tubulars are almost exclusively used by racers… as a chase car complete with mechanic and spare wheels is seldom far behind. But even race teams are beginning to embrace tubeless tire / rim combinations — In some case because of sponsor demands and in some cases for budget reasons. Eliminating the need for separate “race” and “training” wheels decreases the number of wheels needed to be maintained by the team’s mechanic’s staff.
Hookless rim / wheels have been “a thing” in mountain bikes for nearly 10 years, but they are just growing in popularity in the road bike community, especially in gravel applications. A hookless rim is kind of what it sounds like. A rim profile that forgoes the traditional hook of a clincher rim / wheel but that also has “shoulders” that stretch the tire around its circumference to form a seal.
The upside of a hookless rim is that is has shown to be more impervious to impact and it simplifies the construction process, especially in carbon fiber wheels. And according to ZPP, a leading manufacturer of high-performance carbon fiber bike wheels, reduces the cost of manufacturing.
What that means is that hookless rims are tubeless ONLY. It is NOT RECOMMENDED to use a tube and non-tubeless tire with a hookless rim. They require a tubeless tire that meets specific design criteria and materials.
Generally speaking a tubeless tire is stiffer in the sidewall than a clincher tire, making it less supple. This is because the system depends on the tire stretching over the “shoulders” of the rim, mating the tire with the rim to form an airtight seal.
And, like all tubeless tire / rim combinations, they require sealant and specialty rim tape. The sealant completes the tire system by preventing air from escaping through the pores and small imperfections in the tire. The adhesive-backed rim tape prevents air from escaping through the spoke holes of the rim. Sealant also provides a level of puncture protection by using the tire’s internal air pressure to force sealant through small punctures when they occur.
A word about sealant. Most sealants are made of natural or synthetic latex and contain cellulose, rubber particles or organic thickeners and glycol which acts as a liquid carrier for the suspended particles. Most are highly basic, not as in simple, but as in the opposite of acidic on the Ph scale.
When the tire is punctured, the internal air pressure of the tire forces the liquid sealant is through the hole, and a small amount escapes. When this happens the fibers or small particles build-up at the site of the puncture and intertwine to form a flexible plug. Then a chemical reaction happens that “cures” the rubber and fills the puncture.
At least that’s what is supposed to happen. When the puncture is too big, the sealant is old, or there is not enough un-cured sealant in the tire… then not so much.
OK, so that was more than a word. But hopefully you learned something.
BONUS: If you want to avoid getting stranded by the side of the road having to wrestle a tubeless tire off your wheel, cleaning what will inevitably be the foul-smelling remnants of your sealant out of the tire and trying to get a tube in without getting a “pinch flat.” Change your sealant and clean out the inside of your tires every 6-months. Oh, and keep a pair of nitrile gloves in your seat bag so you don’t get that goop on your hands.
A.V. Schmit: Writer, Designer, Cyclist, Triathlete, Profoundly Picky Mechanic, and Lover of Greyhounds
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