Dirt Rider - 2001 Honda CR80R Before
Dirt bikes are a whole different world from the automotive industry. Basically, Dirt Rider's readers can walk into any motorcycle dealership and buy "Formula 1." Just about any production motorcycle designed for the rigorous world of motocross racing is fully capable of racing at the highest levels of motocross (outdoor, closed-course racing on a rough course with right and left turns and a variety of natural and man-made jumps) and supercross competition (usually indoors, but also outdoors on an entirely man-made track with extreme jumps and obstacles). The same is true of racers built for longer looped or point-to-point races off-road. A stock production machine can be entirely successful at the highest levels of competition.
In motocross there are serious race machines for riders as young as six and other models stepping up in size until the racers are required to race against other riders on full-size bikes at age 16. Off-road bikes come as small as 50cc and some weigh well under 100 pounds for small riders and range in size up to 650cc.
Despite all the makes and models, there are a few "holes" in the model line-ups available. A sub-culture of adult minicycle racing is growing like crazy, and radical chassis set-ups utilizing utilitarian, somewhat old-school engines is the latest wave. The same small but race-quality machines appeal to riders who have big talent but desire a small inseam.
Dirt Rider chose to build one of these shrunken racers as our eBay project for a couple of reasons. The most convincing being that there isn't a single production bike like these small racers. They are built in home shops or using specialty frames. The builder must buy a complete two-stroke race bike, then discard the engine, radiator, carburetor and ignition. Then he needs another motorcycle with his engine of choice, and from it he discards the entire rolling chassis! eBay is made for scenarios like this!
The donor bike of choice for the suspension, wheels and frame is the Honda CR80R Expert or CR85R Expert. The plus side is that the engines are highly sought after to build shifter kart racing go-karts. We'll buy a Honda, then sell or trade the engine. There are two ways to go with the frame: Buy an aftermarket model for around $3000 or have the stock frame modified in a precision jig to accept the desired engine. The CR80/85R Expert chassis bikes are the largest of the adult-mini style machines, and the rules allow any engine and displacement as long as it is a two-valve, air-cooled single-cylinder. The most popular choices are all Hondas: The venerable XR200R or similar, but more modern derivatives called the CRF150F and the CRF230F.
We have decided to try a jig-modified frame from DMC in Orange County, Calif. The modified frame comes repainted and ready for the engine of your choice, but includes a manifold, exhaust system and other parts needed to install a bigger-bore trail four-stroke engine in a small-bore racing two-stroke chassis for roughly $2000. DMC feels the older XR200R engine is the best combination of availability, weight and power. An added bonus is the availability of hop-up equipment.
So after we have our CR80 or 85R, we'll search for a good donor bike, and build our adult-mini special.