There have been many questions regarding class structure and the process used to place bikes in the various classes offered by AHRMA. On the surface, the class structure or placements of certain bikes within classes may seem confusing. Illustrating or understanding why the classes have been structured the way they are, and how these decisions were and are being made when adding or moving a particular bike within the AHRMA classes, can be best done by understanding the philosophy used to write the original rules we use today.

The bottom-up philosophy protects certain eras of motorcycles from the motorcycles of the next era that made them obsolete. By starting from the beginning and including all bikes up to the end of an era, we can preserve the era.

The other way to look at class structure is from the top down. This philosophy places bikes by comparison to the best bike in a given class. If the bike being considered is not thought to be as good as the upper models, then it will be moved down to a lower class where it can be one of the best bikes in that class. A major problem with this style of bike placement is that there will always be a (perceived) worst bike in every class, and there will be a desire to move this bike down a class where it will be more competitive. This in turn will push the bottom bikes out of the lower class and so on.

To maintain a fair and consistent class structure, AHRMA uses the bottom-up philosophy. Here is how it works when applied in AHRMA MX class structure. We start with the early days of motocross, when 500cc four-strokes ruled the racetracks, until something came along that made them obsolete. These new bikes were the lighter early two-strokes such as the CZ 360 twin pipe, and a common four-stroke answer to the two-strokes was the lighter unit-single BSA 441.

With hindsight we can clearly see the turning points in MX history. By creating a class to protect the bikes of each era we can in effect "stop time" and keep these bikes from becoming obsolete a second time. Since these changes happen over several years it is difficult, if not impossible, to choose a specific year to draw the line between the end of one era and the beginning of the next. This is true of all the vintage and post-vintage MX classes in AHRMA. Therefore, by using an era-based seperation of classes, instead of strict year cutoffs, we can preserve a given era more accurately, since the bikes from the beginning of the next era will not be included to become (with 20/20 hindsight) the best bike in a class, making lesser bikes obsolete all over again.

Here is an example which illustrates this point as the 250cc machines evolved. The Premier Lightweight class includes 250cc bikes with Villiers two-stroke engines, four-stroke bikes such as the BSA C-15 and Triumph Cub, and several less-common bikes like early Jawas, Maicos and the Honda CL77 twin, among others. Most of these bikes were produced in their original form prior to 1965, and it could be said that 1965 was the beginning of the end for this era of bikes.

But if we say "any bike built before ‘65 is in and all others are in the next class," we will end up with the first bikes of the next era included in the very era they brought to an end. Two examples here are the Husky 250 with bolt-together frame and the CZ twin pipe 250, both produced in small numbers in ‘64. These bikes began a new era in motocross, and that is why they are in the next newer class, Classic 250. The Classic 250 class also includes a bike that is 10 years newer than the CZ and Husky mentioned above, the ‘74 AJS 250 Stormer. The AJS uses the same Villiers engine that fits into the Premier Lightweight class, with a new cylinder and head in a more modern chassis; this combination makes the AJS very compatible with even the earliest CZ and Husky.

The AJS was the end of an era, even though it was produced well into the years covered by the next era, which includes the bikes we call the Sportsman 250 class. Some of the bikes that ushered in the Sportsman era were the newer designs from Husky, Maico and CZ that obsoleted thier own previous models, followed by later entries into the motocross world, including the major Japanese makers’ first efforts at serious production motocrossers.

The Sportsman era ended just before the first long-travel bikes of ‘75 and newer. There are a few examples of ‘74 model bikes with forward-mounted shocks (long-travel), and there are some ‘75 models which remained unchanged in the suspension department.

When the first set of vintage MX rules in the U.S. were drafted in the mid-to-late 1980s, the founders of American vintage motocross studied the defining difference between the old-style short-suspension bikes and the rapidly evolving long-travel bikes and realized the end of another era in motocross had come to pass.

Once the long-travel "genie" was out of the bottle there would be no turning back; this turning point in technology is considered by many to have caused the most rapid evolution of bikes in all of MX history. Many bikes in this new era were obsolete after two or even one racing season, and certainly all pre-long-travel bikes were obsolete within less than a year. This new era, known as the suspension revolution, began (and obsoleted the previous era) more suddenly than all previous eras. For this reason a year cutoff, with a few stipulations, was possible.

This Sportsman cutoff date includes all 1974-model bikes. There are a few bikes that had more than the 4-inch maximum rear suspension travel allowed by AHRMA before the ‘75 models, and these bikes are still allowed in as long as the rear suspension travel is limited to 4 inches. The bikes built after the ‘74 model year that are unchanged are granted entry into the Sportsman class via the like-design rule, which states that if a newer bike is unchanged from its ‘74 model it will be allowed into the Sportsman class. The result is inclusion of all ‘74 models and later bikes that have not been changed from their ‘74 specifications, thus maximizing the number of eligible bikes without giving a suspension advantage to the "early bloomers" such as the ‘74½ Maico.

This philosophy was implemented many years ago, when some of the bikes we now include in our post-vintage MX classes were only a few years old, yet this timeless philosophy gave us the tools needed to create a class structure for the three post-vintage eras that help to preserve each era and give AHRMA members as near a level playing field as can be hoped for in vintage motorcycle racing.