Editor’s note: This story first appeared in Bicycle Times issue #19, published in October 2012. Words by Jeff Archer. Photos by Wes Stearns.
In the last few issues, we have been looking at different frame building materials through the lens of vintage bikes. So far, our series has featured bikes constructed of steel, titanium and a couple versions of carbon fiber. There is a good chance you have owned bikes made of these materials or, at least, kicked the tires of one on your visit to your favorite local bike shop. In this issue, we will look at magnesium, which I would guess is a frame material most of you have not owned before. Some may have used Easton magnesium stems or Avid magnesium linear-pull brakes, but not complete frames.
On paper, magnesium looks like a great frame building material. Magnesium is among the lightest metallic elements, with about half the density of aluminum. The modulus of elasticity (stiffness) isn’t great, but that can be overcome with good frame design. The ductility numbers (how much it will bend before it breaks) are also on the low end, but acceptable. One major issue is corrosion—magnesium will corrode quickly when exposed to the elements. This can be eliminated with careful coating, but it is difficult to completely seal a part against the elements—just about every magnesium part we have seen has “worms” under the finish where corrosion has started. Another potential issue, not so much for the rider as for the builder, is the flammability of the material. Ever notice how every emergency fire-starter kit uses magnesium?
Bike designers will usually find a way of overcoming obstacles in the search for lighter weight. Frank Kirk introduced this frame at the 1986 New York City bike show. With its exotic material and unique style, it was an instant hit. It was claimed that a cubic meter of seawater contained enough magnesium to build a Kirk frame. Extracting the magnesium took a lot of energy, but magnesium is plentiful, with two percent of the Earth’s crust being made of the material. Norsk Hydro, the world’s largest magnesium producer, invested in the company to showcase what could be done with magnesium. Molten magnesium was forced into large dies, and apparently, it took eight seconds to “build” a frame. Sales were decent and the frames even found their way into the Tour de France, under the Dutch TVM team. Later, frames were modified to make the Revolution, a mountain bike version. There seemed to be some momentum behind the effort, but problems started popping up.
As with the Teledyne Titan in issue #16, small issues arose with the frames. Many of them, especially the mountain bike versions, began to crack. The bonding holding some of the small fittings began to fail, and the pressed-in fittings for the headset and bottom bracket were loosening. Many of these things were minor issues that could have been solved with time and money, but the bike market is unforgiving, and the Kirk slowly disappeared. Since then, several manufacturers have produced lightweight magnesium frames in small quantities. The girder-like construction of the Kirk frame still draws attention, and the bike industry loves to recycle ideas, so maybe we’ll see a modern version that will take advantage of 25 years of manufacturing improvements.
This bike can be seen at the Museum of Mountain Bike Art & Technology in historic downtown Statesville, North Carolina. If you can’t visit in person, check out the collection at www.mombat.org.Tweet Print