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Bicycle tire concepts
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Back in his Formula One days, Mario Andretti was asked what kind of tire he'd be using in the coming season. His reply - "Round, black ones."
We all know there's an enormous amount of technology used in developing all types of tires. They aren't simply round and black. Even bicycle tires have gone the high-tech route. We enjoy better braking and control thanks to these innovations. That high-friction contact between our tires and the road is commonly called traction.
Road bike tires, even cheap ones, are comparatively more expensive than high-performance automotive tires because they simply don't last as long. Auto tires may last 30-50K miles, bike tires 10% of that. Someone pointed out that bikes and bike parts can be cheap, light, or durable, and we get to choose which two characteristics we like.
The easiest way to get a performance boost on any vehicle is by changing the tires. For cyclists, conventional wisdom says that a narrow, high-pressure tire offers less rolling resistance than a wide, low-pressure one, and that's generally true when you compare the extremes. A 38mm hybrid tire, for instance, will have more rolling resistance than a 28mm road tire, but that 38mm tire will ride like a Cadillac when compared to a 23 or even a 28. If you're a competitive cyclist, a discussion of the subtle differences between a 21mm tire and a 23mm tire may be of interest. See the Torelli tire technical page for information on racing tires.
Note that the width on a bicycle tire is much like the aspect ratio found on automotive tires. A wide tire like a 28 or 32mm is also taller. This may be a limiting factor if your bike has dual-pivot brakes. There may not be sufficient clearance for tires larger than 28mm.
Here are some basic tire concepts:
CONTACT PATCH
The contact patch is where your tires connect with the pavement. For a 28mm tire, it's roughly as big as a thumb print. This tiny area is responsible for all your propulsion, control, and braking. Obviously, if you can increase friction between the tire and road surface, you can corner faster. How can you increase friction? Glad you asked!
RUBBER COMPOUNDS
Tire hardness can be controlled during manufacturing by the addition of hardening agents. A hard compound will last longer while a soft compound yields better traction at the expense of a shorter useful life. Soft compounds provide better grip in the rain, also. Some tires have dual compounds, a hard, long lasting center flanked by softer shoulders for better cornering.
TREAD DESIGN
The late Sheldon Brown said that tread design has more to do with marketing than real performance. Unless you're riding on snow, that's probably true. Tread on car tires is meant to move water out from under the contact patch and prevent hydroplaning. Bicycle tires don't go fast enough to hydroplane, for one thing, and for another, their narrow, rounded profile is good at moving water to either side as the tire rolls forward.
If you have to ride on snow and ice, aggressive treads and specialty tires equipped with metal studs are available.
RIDE QUALITY
This is difficult to define when looking at a new tire in the shop, but it's immediately apparent on the road. Some tires have a harsh, unyielding ride. Others are much more supple. It's not always possible to determine this in the shop because some relatively stiff tires give a plush ride. To some extent, you can alter the ride quality by trying various pressures, but be aware of the hazards of over inflation and under inflation.
Some tire manufacturers advertise the TPI count which is the number of threads per inch. A higher number indicates a tire with a more supple ride and may allow for reduced weight.
INFLATION
Tires have recommended inflation pressures molded into the sidewalls. These are not absolutes, so you can over-inflate without fear of damage. The tire and rim will likely hold twice the rated pressure before something fails catastrophically. Please - don't test this!
You might think that an over-inflated tire has less rolling resistance, and to some extent you'd be right. It also tends to skip over road irregularities and may not corner as well. It's more prone to damage from rocks or other sharp edges as the tire doesn't yield.
At the other end of the spectrum, under inflation brings its own problems, though it may be slightly beneficial on wet roads. Under inflated tires are more susceptible to snake bite punctures when a road irregularity forces the tire casing into the rim, resulting in two punctures. Severely under inflated tires can result in snake bite punctures and expensive-to-repair rim damage. A good floor pump with a gauge is your tire's best friend.
TIRE DAMAGE FROM ENVIRONMENTAL FACTORS
Potholes and glass present obvious dangers to tires, but other things damage our tires over time. Commuters who leave their bikes in direct sunshine are familiar with the cracking that comes from long term exposure to sunlight. Ultraviolet light slowly degrades the rubber and can weaken the underlying fabric in gumwall tires. Even if the bike is stored inside, ozone from a nearby electric motor can attack the rubber compounds in a similar manner.
This has been a necessarily brief overview of bicycle tires. For more information, please visit these sites:
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