Stunt Motard Based on a Honda CRF450
In Russia you can count the professional stunt riders on your fingers; besides, the sport is considered new, there is still no single standard for its machines, and there are even fewer specialists who build them. Among those who have achieved recognition, including international recognition, is Marat Kankadze. This article describes in detail the preparation of Marat's new motorcycle, a Honda CRF450. Marat is the only pro rider in Russia whose motorcycles are not only as good as foreign machines but surpass them thanks to unique, sometimes fantastic solutions. That was the case with his first motorcycle, a WR450, and it is the case with the new CRF450.
«The Honda CRF 450 is an experiment. I wanted to see how a Honda differs from a Yamaha, and also to try a motorcycle that is lighter than the WR enduro. I like the supermoto class, which lets you jump and ride stairs, and I like its whole vibe,» says Marat Kankadze.
Today's Honda is a true super motocross bike. In fact, in stock form this model has everything you need to build a good stunt motorcycle: it is light, with progressive suspension characteristics and a powerful engine. There are drawbacks too, primarily the engine's service life, which is short, but in stunt use, when the engine isn't revved hard, it should «live» longer.
The stock wheels of the motocrosser don't suit a stunt motard. Marat fitted spoked wheels from the American company DNA. They are quite strong thanks to their design and good-looking, and aesthetics matter a lot. Some athletes use Marchesini cast wheels. They are lighter but have less durable rims. You always need to start from the tricks the athlete is going to do. If they include riding stairs, cast wheels are unsuitable: they will simply bend. A spoked wheel is cheaper and much stronger, but it doesn't allow tubeless tires, which means you can't do a burnout and burn the tire down completely, blowing up the wheel along with an expensive tube that is hard to find. So with spoked wheels a burnout is done only down to the cord.
Special attention should be paid to choosing the rear rim and tire width. Fitting a 160 mm tire on a narrow rim gives an egg-shaped profile, which means an insufficient contact patch. But if you use a narrow 150 tire on a wide rim, it will be «spread out» and the patch will be larger. If you fit a 150 mm tire on a wide 2.5-inch rim, you get good contact patches in leaned positions, which is an advantage for aggressive circles.
It is advisable to fit soft tires on the front wheel: despite fast wear, they provide optimal grip. The hardest possible rubber is fitted on the rear wheel. It is worth noting that for slow circles and technical low-speed tricks, the tires hardly matter at all.
The motorcycle has four-piston brakes made by TRW-Lucas. Ordinary pads are used: sport pads are unsuitable for stunts, since they need to warm up. A stunt bike's pads must bite without warming up. When practicing stoppies (braking on the front wheel), the work is in an «accelerate–brake» mode, so after repeating the run about ten times you need to let the brakes rest before they fade. The specifics of stunt bike use require more frequent brake fluid changes and positioning the brake reservoir so that air doesn't get into the system while riding on the rear wheel.
Marat uses a 60-tooth rear sprocket with a custom design. The front sprocket is the stock 13-tooth one. For riding around town you can switch to a 14-tooth front sprocket and simply adjust the chain tension.
The front suspension of the motocross bike fully suits Marat in terms of stiffness and other characteristics. The rear suspension is modified: swingarm travel is shortened because the exhaust is moved from the side to under the seat. The motard uses rear stunt pegs, which a single-seat motocross bike doesn't have. For symmetry the exhaust has to be moved under the seat, otherwise the peg on one side would have to be longer, which would mean balancing differently and calculating circles differently. In addition, limiting suspension travel gives the necessary stiffness when doing tricks and protects the muffler from being hit by the wheel.
The Honda CRF450 is a dry-sump motorcycle, but despite this Marat overfills the oil by 200–300 grams above the upper level, since the motorcycle still runs in unnatural positions. Like on motocross bikes, a stunt bike has no speedometer; it is replaced by an hour meter. It is used not only to count service intervals (an oil change is needed every 20 hours). This device also counts perfectly how much time you spent training and how much you spent learning a particular trick. A very handy thing. And an honest one: you can never say «I was training» when you were standing around chatting with friends. You always know how many hours you actually practiced. An important change was made in the engine itself: the flywheel was replaced with a heavier one, and a kit to power the fans was added, since speeds on the lot are not like in motocross, there is no natural airflow and the stock cooling system can't cope, so additional fans help it. Fitting a larger Boyesen water pump impeller increases coolant flow and prevents overheating during burnouts.
The heavy flywheel was needed to give the single-cylinder engine more inertia. A motocrosser is designed to gain speed quickly off the start and rev up. At low revs it stalls easily, and the rider falls as soon as he loads the engine with the brake. Fitting a massive flywheel solves this problem. The engine crankcase is professionally painted bright red. The engine management had to be changed: although the stock Honda unit allows several operating modes, switching maps and getting the characteristics needed for different tracks, they are all intended for motocross use. In stunts, low-end power is needed above all. So the unit was replaced with a Power Commander, which allows adjusting practically all engine parameters. But working with it requires a lot of knowledge and experience. We used the exhaust system from a Honda CBR 600 RR road motorcycle with a modified header shape and tuned the Power Commander on a dyno. But, to be honest, in stunt riding the power losses from changing the exhaust configuration are not that significant.
To avoid burns, we used header heat wrap. The muffler is moved under the seat, which is usually also replaced: the cover must be as grippy as possible. The stock CRF450 seat is very grippy and holds well. At the end of the seat there is a small bend that acts as a foot ledge. Marat used a similar design on the Yamaha, while Ryan Moore adds a leather-covered wooden block.
The subframe bar (also called the «frame» or «12 bar»). The structure is the main load-bearing frame coming off the motorcycle frame. The seat and rear pegs mount on it, and a second part is attached that can be changed in length, width and height, so the result is a two-part subframe, one part of which can be changed depending on the requirements of the trick. Notably, the end of the structure is also removable, which allows fitting a round bar, a flat bar (diamond-shaped) or wheels. The position of the rear pegs relative to the frame was also made adjustable (forward-back, up-down), which lets you find the optimal balance for a specific trick. They are used both for tricks and to protect the motorcycle. The result is a maximally functional subframe bar and equipment.
Protective elements include an engine skid plate and a cage, which you rarely see on motards. Its job is to protect the radiators, which don't touch the ground in crashes but are at risk when riding stairs and are especially vulnerable when riding on the rear wheel around a «barrel», the so-called «table». The cage protects the radiator as well as the red-hot exhaust header from impacts.
A handbrake (a hand-operated rear brake on the handlebar) is an essential element of a professional stunt bike. Marat uses a system with a bracket and a separate caliper.
Exclusive graphics were made for Marat, giving the motorcycle a bright and aggressive look.
Source: Motorcycle for stunt riding / A detailed approach, No. 6 (35), August 2010.