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 Frames & Materials Page: 4 of 4


Design

The most popular frame design is known as the diamond or double- triangle. This design has changed very little since the advent of the saftey bicycle in the 1880s. Paolo explained, "It's proven to be a great use of materials, great for bracing angles, great for strength; it lends itself to being beat up pretty hard and still being ridable." The strength of the design comes from the triangle shapes that make up the diamond design. As Paolo explained, "Structurally, it's quite impressive. If you look at engineers playing with structures, they tend to come back to triangles and since the bike is basically three triangles, it works out to be a pretty strong structure."

While the diamond design is the core of most bicycles built today, some frame builders are experimenting with new variations on this classic design. For example, some carbon-fiber frames are being made with oval tubing, making the bicycle more aerodynamic. New full-suspension bikes have altered the diamond design to allow for a large shock to be mounted on the seat stem. However, most changes to the design are more subtle and have to do with maximizing performance for different types of terrain or uses.

Cannondale downhill frame
IMAGE PROVIDED BY CANNONDALE BICYCLES

The Search For Suspension

Almost since the invention of the bicycle, designers have been trying to come up with ways to soften the ride. In the 1880s, roads were unpaved and tires were made of wood or metal. Although the pneumatic tire helped, inventors were lured by the possibility of adding coil springs, lever arms, swing- mounted rear triangles, bumpers, and other cushioning features to the bike. In the 1930s, designers began to take ideas from motorcycles, like the spring-coil front fork, and adding them to deluxe bikes.

Recently, with the soaring interest in mountain bikes, designers have once again been exploring suspension with a vengeance. The rocky terrain covered by mountain bikes makes suspension desirable once again. However, suspension systems often bring added weight and odd steering and pedaling characteristics. The advent of new ultralight materials, combined with refined designs, have made suspension forks almost ubiquitous on the modern mountain bike. Even the holy grail of "dual-suspension" has been attempted, with the goal of suspending the rear wheel without altering the action of pedaling. Many good designs have appeared, ranging from the venerable pivoting rear triangle to a design where the riders sits on a carbon- fiber beam levered out from the head tube. Though the added weight of these bikes is still a problem, they have earned a growing following for their comfort and handling.


Single-Track and Fire Roads

It's easy to see the differences between a road bike and a mountain bike. However, it's sometimes harder to notice the differences between different models of bicycles built for the same type of surface. For example some mountain bikes have a long wheel base making them more stable at higher speeds but incapable of making tight turns. Bikes like this would perform well on wide-open fire roads, but would have difficulty making tight turns on single-track trails. The length of the wheel base, the slope of the top tube, and other differences in frame design all play a role on the road or the trail.

Ruthie Racing

Ruthie Matthes's bike and equipment are customized to meet her racing needs.

 

PHOTO PROVIDED BY PEARL IZUMI/JOHN KELLY PHOTOGRAPHY


Stress on the Frame

Bicycle frames have to be built to handle a variety of loads. First, the frame needs to support itself and other components of the bicycle. These are considered static loads. In addition, the frame needs to be able to handle the cyclist's weight, the forces of pedaling and braking, and the effects of the road's surface. These are dynamic loads; they are the most problematic for a frame builder since, as the name implies, they move and vary in intensity.


Frame builder Paolo Salvagione explained which areas of the frame take the most stress. "Think of a fork as a crowbar on a head tube. Not only do you have the length of the fork which tends to be 16"(40.64 cm), but you also have half of the diameter of the wheel which is another 13"(33.02 cm), so you have a pretty long crowbar there. So if you're riding down a hill and you hit something really hard you have a long lever working on a very small tube. That tends to be an area where a phenomenally large amount of energy needs to be dispersed." Paolo went on to explain that the energy produced by such a collision could throw the cyclist or damage the tube. Most frames are engineered to handle less common events like this.

Paolo S. RealMedia Clip
Paolo talks about which areas of the frame take the most stress.

The other areas of a frame that Paolo was concerned with were the ones that handle stress over time. These areas are common near the chain line. The continual pedaling action exerts forces on the frame. In addition, these areas must also continue to handle the other static and dynamic loads exterted. Paolo uses his experience and engineering knowledge to make sure his bicycles can handle whatever comes down the road.


 

 Frames & Materials Page: 4 of 4
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