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 skateboard for example, riders may choose to either ride “goofy” with their right foot facing forward, or “regular” with their left foot facing forward, depending upon what feels the 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. “Up to forty riders start the race at the same time” (Spalding 12) at over sixty miles per hour, inches away from each other. Riders can hear the great roar of the dirtbikes as they race towards the first turn; some of which being high-pitched two-stroke engines, while the rest are deep-pitched four-stroke engines, for 125cc two-stroke engines have always 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 the bikes will be classified according to the size of their engine, not how fast they truly 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 Two-stroke engines are considered “outdated” technology, as they are worse for the environment, and produce less torque compared to the new four-stroke model engines. “Today, and even more so in the future, significant and simultaneous reductions of emissions and fuel consumption are the key issues in engine combustion” (Arcoumanis, Constantine, and T. Kamimoto 1)). Because of this, many factory brands such as Honda and Suzuki have actually stopped producing two-stroke dirtbikes as of 2007. Accordingly, 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 bikes were 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, “The two-stroke engine performs twice as many power strokes per cylinder per revolution. In theory at least, this might be expected to produce twice the performance of an equivalent-size four-stroke engine” (Nunney 8). Four-stroke engines were now to one’s facing the power disadvantage. Utilizing the four sequences of induction, compression, power, and exhaust, rather than the two sequences of induction-compression and power-exhaust, produces a smoother propulsion, but not a faster one (Nunney 2). This is because four-stroke engines take twice the amount of time to complete a single engine cycle. So, when riders choose which type of bike they would like to be on, the are deciding between a two-stroke that is either going really fast in the high-range RPMs (Rotations Per Minute) and “four-stroking” (irregularly firing) at low engine speeds when the piston is operating in the low-range RPMs (Nunney 8), 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 the two-stroke was a better bike, and there were just as many four-stroke lovers who swore the same. In today’s day, however, there is no mystery, a 250cc two-stroke engine clearly outperforms 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), which 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-strokes. 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” that will change the world of motocross racing once again. The wait for such a thing still continues…
In the mean time, if you are one of the millions of motocross racers who compete in the amateur 250 classes, you are forced to wait for technology to progress, and desperately hope that daddy doesn’t bring home something like a 125cc two-stroke for Christmas.
Bibliography
Nunney, M. J. Engine Technology 1. Butterworths technician series. London: Butterworth, 1981.
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.
