In the sport of motocross, engines stand divided. Similar to other sports such as skateboarding and snowboarding, there are two ways to ride. On a board, riders may choose to either ride “goofy” with their left foot facing forward, or “regular” with their right foot facing forward depending upon what feels most comfortable to them as an individual. In motocross, there is only one way to stand and ride, however riders may choose the type of engine they prefer. As the starting gate drops and forty riders race for the first corner at over sixty miles per hour, inches away from each other, their heart rate up to around 180 to 190 beats per minute (Spalding 12). Riders can hear the roar of the bikes, some of which being high-pitched two-stroke engines, while the rest are deep-pitched four-stroke engines. According to Sport Bike Racing‘s author, Lee-Anne Spalding, ever since the 1930’s, 125cc two-stroke engines have been allowed to compete along side of 250cc four-stroke motorcycles. Two-stroke engines generally are faster due to the small number of strokes the piston must rotate through in order to complete a combustion cycle. Because of this fact, the 125cc two-stroke is comparable to a 250cc four-stroke engine. Recently in the last two years, however, the AMA (American Motorcyclist Association) has announced that, “both two-stroke and four-stroke motorcycles would be limited to the same maximum displacement” (AMA clarifies proposed Youth racing rule changes for 2007), which means that bikes will be classified according to the size of the engine, not how fast they are. Because of this, 250cc two-strokes are now permitted to race with 250cc four-stroke dirtbikes, giving them an unfair advantage.
The AMA has some reason to do so. With the progression of technology, four stroke engines are becoming more efficient. Two-stroke engines are considered “outdated” technology, as they are worse for the environment, and produce less torque compared to the new four-stroke model engines. Many factory brands such as Honda and Suzuki have actually stopped producing two-stroke dirtbikes as of 2007. Because of this, the AMA was soon faced with a problem, thousands of complaining motorcycle shops that experienced extreme difficulty trying to get rid of the two-stroke motorcycles they had in stock. Everyone was switching to four-strokes and nobody wanted to buy a type of bike that was discontinued. Parts were harder to find, there was no longer any factory contingency paid out to these models, and the bike was simply slower. The two-stroke days had almost come to an end. To compensate for all of this, the AMA created this new rule. Now that two-stroke are on top once again, everyone wanted to buy the fastest bike they possibly could, and the answer was a 250cc two-stroke. Local shops were able to get rid of their sluggish inventory and everyone was happy; everyone except for the 250cc four-stroke riders.
As stated previously, “a two-stroke engine is a combustion engine that completes the thermodynamic cycle in two movements of the piston compared to twice that number for a four-stroke engine” (Heywood 3). Four-stroke engines were now to one’s facing the power disadvantage, for “a four-stroke engine produces a smoother, more reliable, and stronger torque than a two-stroke engine” (Arcoumanis 34), but not faster, because they take twice the amount of time to complete a “thermodynamic cycle”. So, when riders choose which type of bike they would like to be on, the are deciding between a jerky two-stroke that is either going really fast in the high-range RPMs (Rotations per minute) or going really slow, bogging down in the low-range RPMs, or choosing a four-stroke engine that offers reliable torque at all RPM ranges. This was a fairly difficult decision before the AMA’s new proposal. There were two-stroke lovers who swore on their life that it was a faster bike, and there were just as many four-stroke lovers who swore the same. In today’s day, however, there I no mystery, a 250cc two-stroke engine clearly out-performs a 250cc four-stroke engine.
The AMA knows this and did what they did just to help get rid of the 250cc two-strokes that would not sell. The AMA was unaware that they were burying themselves in a hole, because everyone wants two-strokes now and today they are hard to come by since many popular manufacturers have stopped producing them. Accordingly, the AMA has come out with yet another outrageous rule for competitive racing. They have announced that for the 2009 Lucas Oil AMA Pro Motocross Championship, they have “decided not to suggest any immediate changes to the AMA Pro Racing rulebook concerning the 250 Class and the placement of 250cc two-strokes alongside 250cc four-strokes.” (No 250 2-Strokes in AMA MX 250 Class). This means that the new rule only applies to amateur and not professional motocross racing, igniting even more debate.
Through all of this commotion, the manufactures are desperately attempting to improve the four-stroke motorcycles experimenting with such concepts as dual-exhaust and EFI (Electronic Fuel Injection), trying to catch back up with the speedy new two-stroke. Of all the new modifications, EFI is the only option that has shown any signs of long-term improvement, yet every month there is a new article talking about the “next big thing”. The wait continues.
In the mean time, if you are a motocross racer who competes in the amateur 250 classes, (over millions of people (Spalding 160)) you are forced to wait for technology to progress, and desperately hope that daddy doesn’t bring home a 125cc two-stroke for Christmas.
Bibliography
Heywood, John B., and Eran Sher. The Two-Stroke Cycle Engine: Its Development, Operation, and Design. Philadelphia, PA: Taylor & Francis, 1999.
Spalding, Lee-Anne T. Sport Bike Racing. High interest adventures in reading. Vero Beach, FL.: Rourke Pub, 2009.
Arcoumanis, Constantine, and T. Kamimoto. Flow and Combustion in Reciprocating Engines. Berlin: Springer, 2009.
"AMA clarifies proposed Youth racing rule changes for 2007." American Motorcyclist Association (2006): n. pag. Web. 1 Dec 2009.
"No 250 2-Strokes in AMA MX 250 Class." Lucas Oil AMA Pro Motocross 4 Mar. 2009 : n. pag. Web. 1 Dec 2009.
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