Thundercross!
THUNDER CROSS!
Austrian, British and Swedish Thumpers tackle America's tour-strokes-only Sound of Thunder motocross series
JIMMY LEWIS
I LIVE FOR RACING, ESPECIALLY WHEN IT involves roost-churning, flame-throwing fourstrokes. So when the opportunity presented itself to evaluate the latest batch of factory Thumpers from Husaberg, CCM and KTM in the AMA’s Sound of Thunder motocross series, I already had my gearbag packed. Three bar-banging weekends with a bunch of the fastest four-stroke motorcycles and riders in the U.S.? I wouldn’t miss it for the world.
First up was the $7445 Husaberg FC501. Even in showroom-stock form, the Swedish Single is pure racebike. Still, set-up plays an important role. The most exotic bike that I raced, my Husaberg differed from factory rider Mike Young’s machine only by virtue of his bike’s special FMF exhaust pipe and titanium-nitride-coated WP fork. My bike’s liquid-cooled engine was stock, save for some mild porting and valve lapping. A nickel-plated FMF pipe shifted power up higher in the rpm range for additional over-rev, and the clutch was modified for a lighter pull at the lever.
FMF also re-valved the suspension. The fork was slightly stiffer, compliments of .46kg springs (stock is .44kg), while the rear shock used the standard 5.3kg spring. Other changes include a Renthal handlebar, grips and sprockets. A Guts seat cover replaced the stocker. There was plenty of titanium, including a hand-fabricated subframe that offered a 2-pound savings. The rear axle and many fasteners were Ti, too. Pirelli tires were mounted front and rear; an MT32A up front and an MT32 out back.
At Southern California’s Glen Helen Raceway for the White Bros. Four-Stroke World Championships, my borrowed Husaberg was the fastest bike on the track. Despite a lOOcc displacement deficit to most of the competition, I was second into the first tum in both motos. (The leader also was Husaberg-mounted.) Power was phenomenal. The engine pulled from near zero to valve-float with arm-jerking torque. Revs built quickly, too-not quite as rapidly as a two-stroke but much better than any four-stroke I’d ever ridden. It was a terrific combination: all the hooked-up acceleration of a Thumper with the snappy response of a two-stroke. Call it a “three-stroke.”
The Husaberg chassis felt totally at home on a motocross track. With its sharp steering and rigid frame, the FC would quickly cut an inside line or skim across the tops of bumps. Suspension settings, however, were a bit tricky. On the fast, relatively smooth track, there was a bit of mid-stroke harshness both front and rear. Overall, though, the bike was set-up so well that it often conned me into riding faster than I was prepared to.
Like any Thumper that is ridden past the edge of control, the 501 quickly reminded me that it is not a lightweight 250cc MXer. Indeed, there was little chance of saving a big mistake-don’t ask me how I know. Despite the crash, my results at Glen Helen were pretty decent-fifth place overall despite not-so-good moto placings. It’s good to see that consistency still plays a big role in fourstroke motocross.
At Hangtown for the 125/250 National, the Thumpers were squeezed into the program as a support class. My ride, CCM’s C-25, was completely stock. Stock? Yep, that’s how the late Donny Schmit raced the bike to the series championship last year. As for me, a larger pilot jet to handle air conditions, stiffer fork springs and a new set of Dunlops brought the bike up to snuff. At $7230, the CCM is closer to start-line readiness than one might imagine.
Despite its heavy Rotax powerplant, the 604cc CCM felt amazingly light. Credit a simple design. The bike has no shock linkage, and cylinder fins handle cooling chores. Although it felt down on power compared to the Husaberg, the engine worked best when the five-speed wide-ratio transmission was short-shifted. The lack of rpm made the bike feel slow, but the engine’s big power pulses went a long way. Starts on the loamy uphill straight were mid-pack, but once the competition thinned-out, there was plenty of
power to get the job done. The track was super rough, so choosing suspension settings was difficult. There were tons of small braking bumps and huge jumps with flat landings, so settings that delivered low-speed suppleness allowed the bike to bottom on big landings.
No matter how hard it bottomed, though, the CCM always tracked straight. Turning was basically pointand-shoot. Confidence came easily. I could move all over the bike-forward in the turns and absolutely anywhere in the air. Complaints? The footpegs were too low, and toward the end of each 30-minute moto, the reservoir-equipped shock began to fade. Still, I nabbed fifth place overall (again), the highestplacing CCM rider.
Back to Glen Helen for round four of the Sound of Thunder series and a swing at KTM’s 620SX. The track was all-new, as was the $6478 Katoom. The 612cc liquid-cooled motor was basically stock, but with the micro oil filter removed and oil lines from an ’89 LC4 fitted in the interest of shaving off every ounce of weight. For crisper throttle response, a modified Dell’Orto flat-slide carburetor was fitted, along with an FMF pipe. The airbox was opened up a bit, too, improving flow.
Up front, the stock triple-clamps were replaced with machined-from-billet pieces from KTM’s 250SX, which offer additional clamping surface and less fork offset. KTM revalved the stock rear shock for more progressive action, while the WP fork went untouched, save for 15-weight oil. Looks-wise, the K-style graphics kit and seat cover matched Lance Smail’s factory racebike. Finishing touches included a Renthal handlebar, a purple EK O-ring chain and Sunstar sprockets.
During the first practice, 1 was fighting the KTM. But a gearing change and a more triangularly knobbed Dunlop K755 front tire fixed everything. Although the engine revved slower than the Husaberg’s, power was never a problem. The SX was, however, slower to the first turn; blame it on an extra shift.
The KTM’s suspension was the best of the three bikes I raced. Damping rates were spot-on, though the fork bottomed a little too often. And even though the bike felt heavier than the others, it soaked up anything I tossed its way. Even “Animal Leap,” a two-story, downhill double-jump, presented no problems. With its roomy layout, the KTM, like the CCM, has a very “four-stroke” feel to it; compression braking aids comer set-up, slides are ultra-predictable, and fast laps require high
cornering speeds and smooth lines. The consistent nature of the competition resulted in a seventh overall, moving me into the top 10 in points despite missing the first round of the series.
Just a few years ago, converting a four-stroke trail or enduro bike into a competitive motocrosser would have cost plenty, both in time and money. Now, Thumpers are highly competitive, reliable and readily available at your local motorcycle dealer. As the Sound of Thunder series has proven, four-stroke motocross series are gaining momentum, providing exposure for some of motorcycling’s less-prominent manufacturers. With three rounds remaining and an East/West shootout still to come, I only have one problem: I need four more testbikes. Any takers? □
THUMPER PHOTO GALLERY
Sound of Thunder outtakes (clockwise from top): Where is 1986 125cc National Motocross Champion Mickey Dymond (181) these days? When the free spirit isn’t writing poetry, he’s racing a Husaberg Thumper. Kawasaki’s off-road ace Ty Davis (26) made the Hangtown round on a Stroker Kawasaki KLX340. His
motocross roots are still with him as he took a solid third-place finish. Is the racing close? CCM’s hired gun,
Billy Liles (117) demonstrates that racing Thumpers isn’t a walk in the park—it’s a bar-banging, knock-down race to the checkers. Husaberg’s Mike Young (273) is in the Sound of Thunder driver’s seat, leading the series with three rounds remaining. A year in Europe competing on a Vertimati in the 500cc MXGPs has taught the sometimes CW test rider to match consistency with speed. Spud Walters (64) has been putting in impressive finishes on the ultratrick White Bros. Honda XR400. Walters’ hard riding more than makes up for the Honda’s smaller displacement and lack of power
compared to the big bikes. KTM’s Lance Smail (79) is the fastest guy on the track—when he’s not picking himself off the ground, that is.
Trying too hard and the resulting crashes has cost Smail the series points lead.
