What Killed the Two-Stroke Motocross Bike and What May Bring it Back

January 12th, 2009 • Comments My Thoughts
Tags: Buckley, economy, four-stroke, green, Jeff Emig, two-stroke, Zero

The two-stroke motocross bike is all but dead. The epic staple of the motocross industry from decades ago is now an aging relic. The trademark br-a-a-a-a-a-a-a-p of a properly tuned 125cc two-stroke motocross bike is now a rarity, and the four-strokes have already begun their assault on the mini bike classes.

-Photo by Paul Buckley.

The fact that two-strokes are quickly becoming an antique in the motocross world is undeniable. But what exactly killed this ingenious technology? Two-strokes are lighter, faster (at the same displacement), cheaper to buy and maintain, and easier to work on. On paper they are a clear victor over the louder, heavier, more expensive and more complicated four-strokes. So, what exactly is responsible for the demise of the two-stroke?

Racing Organizations (AMA/FIM)

When the four-stroke was first introduced, it was a joke. Heavy, expensive, loud and slow. Riding one was more of a way to make a statement about your personality than to actually ride the best bike available. So, racing organizations such as the AMA and FIM felt it necessary to give them a (huge) handicap. Almost double displacement for Motocross/Supercross class and exactly twice the displacement for the Lites classes. At the time this felt like a sensible move. The newer technology needed the extra motor size in order to even be remotely competitive.

The problem with the assumption by the AMA and FIM that the four-strokes are slower by nature is that it is wrong. Sure, you can make an argument that the piston travels four time as far for one revolution, but in practice, four-strokes can produce almost the same amount of power as an equally displaced two-stroke. As technology has evolved, the twice as large four-stroke engines have rocketed ahead of two-strokes, making two-strokes too slow for serious competition in the pro or national amateur levels.

Read more »