Technological innovation is a huge part of the automotive world. Ranging from when motorcycles and automobiles were crank starts and  came in one color to automatic pedestrian detection, we've come a long way in getting the most performance and safety out of vehicles. A major innovation of the past half century also comes from the metals used to construct motorcycles. We'll discuss alloy frames – using a blend of metals to produce a durable, flexible, and light frame for a modern motorcycle.

What is an alloy?

Most would define an alloy as a mixture o f metals. While a variety of goals can be accomplished with a variety of mixtures, an alloy is often made to produce a stronger metal, a more flexible metal, a metal that cuts metal better, and the list of possibilities goes on and on.

Prior to the 1980s, most motorcycles were made with steel frames. The frames were heavy, often weighing a few hundred pounds. They required a bigger engine just be able to move the bike adequately. The result was a not especially well balanced speed machine – and you can see it in some racing and speed videos – the bike is wobbling because of an imbalance of weight.

Why aluminum as an alloy for a motorcycles?

Alloys like aluminum can be engineered in multiple ways. Drivers of fast motorcycles want a stiff frame that won't feel like it is bending under the load and torque of an engine and tires. It's also softer than steel and much lighter. Steel weights 490 pounds per cubic foot while aluminum tops out at around 190 pounds per cubic foot. The lesser weight makes it possible to either equip a motorcycle with a smaller engine to attain the same top speed, or equip it with a bigger engine to go even faster. The lack of weight also gives manufacturers to opportunity to add other equipment that could add weight too.

Aluminum could help in crashes, too. A steel frame could bend if it fell, causing damage and the riding dynamic to be incorrect – in addition to possibly breaking parts. A fallen aluminum frame would be more flexible and unlikely to sustain damage if crashed.

One huge advantage for a machine that could be parked outdoors was that aluminum doesn't rust. A steel framed motorcycle that sits out in the rain for years has a higher chance of rust, eventually making the motorcycle unstable and vulnerable to major issues. An aluminum motorcycle doesn't mind weather changes, including rain.

How did the switch from aluminum to steel happen? 

Steel used to be easier to work with – and cheaper. That was until the late 1970s, when aluminum moldings became much cheaper and easier to work with. When the two became nearly equal in production costs, aluminum took over because the lighter weight frames would naturally be better on a motorcycle. 

The process of switching to aluminum was relatively slow. Aluminum wasn't easy to work with at first, and could result in pores in the metal that offered inconsistent strength and durability. Engineers figured out a way to push the gas and oxygen out of aluminum moldings – by using vacuums and pumps to remove the offending bubbles out as the molds were being poured.

Which bikes introduced alloy frames?

Aluminum entered motorcycle lore in the 1970s when Kawasaki began to use aluminum in swing arms for its MX. Yahama then provided Kenny Roberts, a championship racer with a frame made of an extruded aluminum tube. At first, aluminum was expensive and only used in super bikes in an effort to limit the weight in a powerful motorcycle. Eventually, alloy frames became very common because the cost of materials went down significantly while the quality of the aluminum frames went up.

Are there any disadvantages to aluminum?

Alloys like aluminum transmit the vibrations of a motorcycles differently. Some true race drivers think that aluminum “feels” different and a bit more numb to feedback. Drivers who grew up in a time when primarily alloy frame motorcycles were available might feel differently, having only used them.