Fifty-five horsepower pushing...
Fifty-five horsepower pushing a 250-pound package makes Formula 450 roadracers a blast on tight tracks like Willow Springs' Horse Thief Mile.
Learn To roost The Roadrace Track In One Easy Lesson
4 Kawasaki KX450F Roadracer
While the other bikes in this feature bear at least a vestigial resemblance to their motocross ancestors, you'd hardly guess there's an unaltered dirtbike frame and engine lurking under a Formula 450 roadracer's aerodynamic skin. Even more unexpected is how well these radically reconfigured machines navigate a road course. A few laps on a properly fettled F450 bike might convince you that roadracing is the most inspired mutation to dirtbike DNA yet.
Surprisingly few changes are required to complete an F450 conversion. You'll need 17-inch wheels to accommodate roadrace rubber, plus an oversized front brake. Clip-on handlebars and rearset footpegs are a must to create a roadrace-appropriate riding position, and bodywork is a no-brainer now that Catalyst Racing Composites manufactures kits to fit all popular 450cc 'crossers.
Rolling your own F450 is essentially a bolt-on endeavor, save for suspension. Contrary to popular belief (and earlier efforts), you cannot successfully re-purpose sportbike components. Sportbike forks are too short, which takes away too much trail (degrading front-end grip) and excessively flattens the swingarm angle (making the bike squat too much under power). A better solution comes from Paul Thede at Race Tech, who spent countless hours analyzing F450s on his in-house chassis dyno to develop a turnkey tuning package that reconfigures the stock motocross suspension for roadrace use.
Technicians internally shorten the stock shock, fit it with a shorter, stiffer spring and re-valve it using their proprietary Gold Valve technology. The fork legs are also shortened, and likewise retrofitted with Gold Valves and stiffer springs. New triple clamps radically reduce offset to increase trail (lessening the tendency to tuck the front), and new fork bottoms have provisions for mounting a radial brake caliper. Lastly, Race Tech machines the tapered upper fork stanchions to a constant diameter to accept clip-ons. The result is an effective roadracing tool with near-flawless handling and a power-to-weight ratio to rival most 600cc sportbikes: 252 lbs. full of gas and 55 bhp with an FMF pipe and mild fuel-injection tuning.
We rode two F450s at the Willow Springs Horse Thief Mile: Max Capps' 2009 Kawasaki KX450F-based machine, as well as an '08 Suzuki RM-Z450 belonging to Gavin Trippe, promoter of the legendary ABC-TV "Superbikers" events, who now proselytizes about F450 movement at www.450moto.com. Capps' brand-new bike was a stunner, bristling with hand-machined components, but zero set-up time (he literally finished assembling it in the paddock that morning) meant the handling was less than optimal. Trippe's well-developed RM-Z, on the other hand, was a revelation. Imagine a more stable, less twitchy (but still very agile) 250cc Grand Prix bike with a powerplant every bit as torquey and tractable as a Suzuki SV650--that's essentially what an F450 feels like at speed. Nothing brakes better than a bike this light, and abundant cornering clearance, coupled with right-now responsiveness that's only possible from a 250-pound package, encourages tight lines and high corner speeds that result in surprisingly quick lap times.
 Motocross motors are simple...  Motocross motors are simple to wrench on compared to conventional sportbikes. The single-cylinder engines have proven surprisingly reliable for roadrace use. |  Geared for roadracing, an...  Geared for roadracing, an F450 racer will pull around 110 mph on top. Ironically, a 450's swingarm is almost exactly the same length as that of a Yamaha TZR250 Grand Prix bike. |  It's not all big-bucks bling:...  It's not all big-bucks bling: Take-off Tokico four-piston radial brake caliper was purchased on eBay for just $5, and is more than adequate for slowing this little machine down. |
The easiest way to get into F450, Trippe says, is to buy a used supermoto bike fitted with 17-inch wheels and an oversized front brake. Add bodywork ($1100) and suspension ($2500) and you'll be race-ready for well under $10K. To go the fresh-and-tasty route like Capps, double that figure. Not exactly pocket change, but that's substantially cheaper than a similarly outfitted 600, and the operating costs are much lower--tires last at least three race weekends, Trippe claims, and you can run all day on 4 gallons of gas. Such advantages have Trippe lobbying hard for F450s as a more affordable and accessible alternative to the (now-discontinued) Red Bull Rookies Cup and the AMA/DMG's new under-21 Supersport class (which attracted just seven entries at California's Auto Club Speedway the weekend after our test). These bikes also make competitive Formula Singles-class racers at the club level.
"Formula 450 is a great way to encourage young riders," Trippe proclaims. "It's back-to-basics racing, emphasizing riding skill over horsepower, and you don't need a six-figure sponsorship just to make the grid."
Think of Formula 450, then, as a new--and even more literal--twist on the old adage that dirtbikes are the most direct route to future roadracing success.
Kawasaki KX450F Roadracer
What You Need
17-inch wheels with roadrace slicks, oversized front brake kit, lower/firmer suspension, triple clamps, roadrace bodywork, rearsets, clip-ons, axle/frame sliders, taller gearing
What A Pro Needs
Motor work, pipe, slipper clutch, steering damper, mag wheels, radial front brake caliper, custom paint
How Much
$10,000 to drag a knee$20,000 to land a magazine feature
Mini Mille
Not feeling the thumper vibe? You can also roll a V-twin variation of the F450 concept based on the Aprilia SXV 4.5 supermoto, which is what Roland Sands did. The same excellent handling and favorable power-to-weight characteristics that typify the single-based 450s remain intact, though the quicker-revving V-twin changes the bike's character completely. Spoked wheels are an elegant touch, and exhaust outlets frenched into the tail section remind you that Sands is not only a former AMA 250cc Grand Prix champion but a gifted customizer as well. Now, if we could only try one based on the 550cc SXV 5.5...
Two By Two
Why did Roland Sands Designs fabricator Rodney Aguiar adapt a Christini all-wheel-drive system to his Honda CRF450R-based roadracer? "I just wanted to see how it worked on pavement," he says. A mechanical reduction allows the front tire to free-wheel until the rear tire spins more than 8 percent, at which point the front drive is engaged. Where the concept is proven off-road, it's mostly a novelty on a 50-bhp roadracer. We detected only a slight difference at deep lean angles, where throttle applications improved steering and stability instead of further overwhelming rear grip. Perhaps we should have run it into a gravel trap?