"Mags" For Motorcycles:
"Mags" For Motorcycles:
How They Came About
"MAG WHEEL" is a term loosely used in the automotive world to designate almost any cast wheel, but because of the high cost
of magnesium and its alloys, aluminum is the most popular metal in general use.
Cast aluminum wheels for motorcycles would have to be of much larger wall thickness, and consequently much heavier, than an alloy of magnesium, but would have the advantage of being stronger than a wire spoke wheel. They could also be run tubeless and might be more pleasing aesthetically.
Flexing of a front wheel at certain points in the curve can cause a road racer to lose traction and crash, according to Monotrack Engineering’s Brian Littler. He learned of this phenomenon by studying a film of several rider’s spills in the Parabólica Curve at Monza, Italy. So he set out. to do something about it. A cast wheel seemed to be the answer.
“For simplicity’s sake, a wheel was made of sheet aluminum with an undimpled and undrilled Borra ni alloy rim. The wheel was run at Monza without brakes and the results were encouraging enough for me to pursue a means of making a stiffen wheel,” says Littler.
A foundry in Germany which made turbine impeller blades cast, up an aluminum wheel with an adapter for sprockets or disc brakes, but it weighed 26 lb. With the disc brake and caliper, the
assembly weighed a gargantuan 45 lb., and due to the vane shape of the spokes, it made a low-pitched howl at speeds of over 20 tophi
Soon after, the number of the “blade” spokes was cut by 50 percent, and the foundry foreman, a motorcycle enthusiast himself, introduced Brian to his Wundermetal, Elektron. This alloy is composed of 45 percent magnesium, 52 percent aluminum, I percent manganese and 2 percent zinc. The new wheel, with
a vented automobile-type brake disc, cut the overall weight down to 30 lb. Another advantage: the blades set up a turbulence behind the machine, making it difficult to draft the rider. But the wheel was costly and therefore did not sell. Development was postponed for a few years.
Littler returned to America a couple of years later and adapted an American racing mag wheel with a Lockheed disc. And he became convinced that American metallurgy was the answer to the problem: “This country is the sole source of magnesium sponge, and Dow Chemical is the only supplier of suitable magnesium alloys in the world.”
Getting to know Ted Halibrand and lorn Griffith helped him a great deal,
and he soon had several different designs. But the battle had just started: “Another wheel was made while I was at Tabloc which was a derivative of an earlier six-spoke wheel, but then Dan Hanebrink pointed out some inherent design weaknesses •of all mag motorcycle wheels. The most important of these concerned the strength of the spokes where they intersect the wheel rim. Tapering the spoke towards the rim was the worst possible thing to do, especially with only six spokes.”
A light and rigid wheel is the aim of Monotrack Engineering, which claims that their wheels are '20 times as strong as a conventional wire wheel, and weigh (depending on the size) as little as 6 lb.
“In cross section,” Brian says, “the Borrani rim, primarily a street and motocross rim, is half the thickness of an Akront rim, the only suitable rim for desert competition. Based upon this knowledge, and the comforting thought that our own magnesium alloy (91 percent magnesium) is stronger than an equal thickness of aluminum, we decided to build in a tremendous strength and safety factor by making our rim
thicker than the Akront rim. The lightness of the magnesium still gave us a lighter wheel where it really counts, around the periphery.
“At this point it should be noted that the elongation or elasticity of our alloy exceeds 13 percent, which is not approached by the most exotic aluminum alloy. This elongation, or ability to ‘roll with the punches,’ is an absolute necessity, and destroys the old brittle image of wartime magnesium. I understand, however, that there is currently an aluminum alloy being produced in England with an elongation approaching I 1 percent.”
Three claimed advantages to running mag wheels are:
1. The ability to run many tires tubeless, which reduces the rate of deflation of the lire under blowout conditions, and contributes to the rider’s safety.
2. Rigidity, which improves the stability and handling of a motorcycle.
3. Lightness, in the critical area of
unsprung weight, which improves suspension characteristics and handling qualities.
