Wheels

Wheels (cont)

Tangential & Radial Spokes

There are many different ways to spoke a cycle wheel. Most cycles have tangential spokes, meaning that the spokes do not connect from the hub to the rim in a straight line, but at an angle. There are many different patterns of tangential spokes. Occasionally cycles will have completely radial spokes. These spokes go straight from the hub to the rim of the tyre. Wheels typically have tangential spokes. The way in which the wheels are spoked determines how they will perform.

"You can spoke the front wheel completely radially, but the rear wheel had better not be spoked radially. There is no way to convey the twist of the wheel out to the rim to drive you forward," Exploratorium Senior Scientist Paul Doherty explained. Tangential spoking helps transmit the torque from the hub out to the tyres.

Not only would a radially spoked rear wheel be less efficient than one spoked tangentially - it would be significantly weaker. A cycle wheel needs to be able to handle a variety of forces. Besides holding up the weight of the cyclist, a wheel must withstand the forces of pedaling and braking and the jarring effects of the road surface. The benefit of radial spoking has to do with the stiffness of the wheel (less deformation makes the wheel slightly more efficient).

Tension not Compression

It's easy to think of the spokes as columns supporting the wheel and helping it retain its shape. But, the "support" that the wheel receives is created by pulling the spokes towards the center of the wheel (tension) rather than pushing out from the center (compression). If you've had the occasion to hold a spoke that was removed from a wheel, you've probably noticed how flimsy it is. You could bend one in half without too much effort. However, if you tried to pull one apart you would not be able to. The "pulling" of the spokes toward the center of the hub is what gives the cycle wheel its strength.

So just how strong are cycle wheels? "Wheels, from what I remember, can hold about 400 times their own weight on a regular basis and they won't collapse until roughly 700 times their own weight, which makes them one of the strongest man-made structures on the planet," explained cycle maker Paolo Salvagione.

Pneumatic tyres

The pneumatic (or air-filled) rubber tyre is something we take for granted today. Almost every type of cycle wheel has a pneumatic tyre on its rim. The development of the pneumatic tyre was an important landmark in the development of the modern cycle. Prior to its invention in 1888 by John Boyd Dunlop, bicycling was a bumpy and somewhat uncomfortable experience. tyres were made out of leather (and later solid rubber) attached to a wood or metal rim. The air-filled tyre brought with it a smooth, comfortable, and stable ride. It's no surprise that it also helped make bicycling more popular.

Are your tyres fat or thin?

Depending on the type, your cycle has either fat tyres or thin tyres. Most road bikes and touring bikes have thinner tyres, while mountain bikes have big fat tyres. Each type of tyre has been adapted for the surfaces they ride on.The road tyres are inflated to 100 or even 120 PSI (pounds per square inch). A firm thin tyre on the asphalt surface won't flatten much. The less the tyre flattens out on the bottom, the less surface area is in contact with the road. Less contact in this case means less friction, and more speed. This is why keeping tyres properly inflated is so important.

Wide and fat mountain bike tyres flatten out more on a hard asphalt surface. However, on a dirt trail, a mountain bike tyre "floats" on top of the rough surface. A thinner road tyre would cut deep into the dirt, forcing the cyclist to pedal her way out of a hole.

It is easy to imagine a pneumatic tyre "flattening out" on the bottom as it rotates. But surprisingly, steel train wheels on a steel rail experience the same effect. The temporary flattening-out of the wheel, as well as sinkage on the contacting surface, is what leads to "rolling resistance." This term is used to describe how much energy is "lost to the road" as a wheel moves forward. tyres with low pressure traveling on soft ground tend to have higher rolling resistance. This one of the major reasons why road racing is a faster sport then mountain biking.

Tyre treads

The treads of mountain bike tyres can affect performance. Rough or "knobby" treads grip dirt trails better, but create greater friction on smooth roads. Smooth tyres grip smooth roads better, with less resistance, but slip on dirt trails. Mountain bike tyres manufacturers produce a variety of different patterned nobby treads. While cyclists have different preferences, there has been little scientific support for one tread performing better than another.