The Wr400 Factor
The WR400 Factor
CW PROJECT
Yamaha’s Wide-Range Thumper
DON CANET
It’S BEEN A LONG TIME SINCE Thumper fans and serious motocross racers have marched to the beat of the same drum. Yamaha’s lightweight, revolu-tionary YZ400F, though, has set a new tempo and changed the way offroad enthusiasts view four-stroke dirtbikes. Already a proven winner in various dirt-racing disciplines, the liquid-cooled, dohc, five-valve MXer has quickly gained a reputation for being a powerful and lightweight two-stroke stomper. When White Brothers R&D head
Gary Jones approached us with the idea of converting one of the YamaThumpers over to dual-purpose duty, we immediately jumped on the bandwagon. With the bike’s off-road prowess already established, we wanted to try something a bit different, though. Perhaps a more street-based package, a bike that could be ridden on roads or trails, yet be competitive at amateur-level flat-track, TT, SuperTT or even Singles-class roadracing.
While our sights were set on YZ400F engine performance, it
made more sense to begin with a WR400F, the YZ’s re-tuned enduro stablemate. Not only is the WR’s wide-ratio gearbox better suited to high-speed operation, but the bike also comes fitted with such streetworthy items as a sidestand, stator, headlight and taillight.
Chassis-wise, the YZ and WR are nearly identical-same frame, same brakes, even the same suspension components, although the WR’s calibration is softer. While purpose-built dirt-trackers sit quite low, such a setup would make our bike too narrowly focused. After all, we weren't attempting to build an all-out XR-750 beater, more a jack-of-all-trades, mas ter of fun...
Iheretore, most ot the WK4UU's suspension travel was retained to pre serve its general trail-riding capabili ty. Internal spacers were installed in the fork and shock, lowering the bike 1 inch at each end. Higher-rate Eibach springs firmed-up the suspension for improved handling and feedback when ridden hard on pavement or graded dirt roads. Valving was left standard since the external suspension adjusters offer a fairly broad range of damnin adjustment
A set of White Brothers wheelscomposed of matching gold-anodized Takasago Excel rims and Talon billetaluminum hubs-completed our bike's aggressive SuperTl stance. Up front, a 2.15 x 19-inch rim replaced the standard 21-incher and a slightly wider 2.5 x 18 brings up the rear. Pirelli MT6O dual-purpose tires were mounted for the first few outings. Fairly road-biased, the MT6Os deliver good grip and predictable slides on asphalt or blue-grooved dirt. With the chassis mods complete, Jones shifted his efforts to boosting the WR's power output. YZ-like perform ance resides within the WR motor; it's simply a matter of retarding the exhaust-cam timing (by one tooth to YZ-spec) and bolting on a free-flow ing WB E-Series exhaust. These changes, along with a WB Powerfilter. netted a 5-horsepower increase across the range between 5000-11 000 rpm. With peak power readings of 45 horse power at 8900 rpm and 29 foot-pounds of torque at 7000, we were revved up and ready to race.
A few cosmetic touches were all that remained in preparing for our first SuperTT event at Willow Springs Raceway. A couple of inches trimmed off the front fender complements the supermotard look, and a White Brothers YZ400 decal kit adds visual impact-WB doesn't offer WR stick ers. With Jones and I sharing the rid ing chores, we won our respective classes: Senior and Middleweight Supermotard. It was apparent that Jones, a four-time AMA National Motocross Champion. was hooked on SuperlT's exciting blend of roadrace and dirt-track-style action. "The com bination of dirt and pavement results in plenty of passing. It's a great equal izer, as the advantage constantly shifts between riders who favor one surface to the other," he said.
Like on many MX bikes, the WR's stock front brake rotor isn't up to the rigors of racing on pavement. By the end of the weekend it had warped into a dish shape. A WB front-brake kit was installed in preparation for the following SuperTT at Buttonwillow Raceway Park. The larger diameter and added thickness of the kit's 320mm floating stainless-steel rotor delivers excellent stopping power and warp resistance. The kit includes a bil let-aluminum hanger to properly locate the stock caliper for use with the larger rotor. A set of Galfer kevlar brake pads proved to he a very good addition to this setup.
Buttonwillow's 100-mph straight called for a 15/41 -tooth sprocket corn bination. This final gearing also served quite well when we ventured out onto the street between race outings. White Brothers sells a dual-sport kit for the WR that comes complete with DOTapproved headlight, taillight and tumsignals-the WR's enduro lighting doesn't meet the vehicle regulations in certain states. Also included are han dlebar switchgear, sealed battery, volt age rectifier/regulator, horn, brakelight switch and a complete wiring harness that plugs into the existing loom. Since our testbike wasn't.. .ahem.. .Iicensed, our actual riding time on public roads was very limited. At least that's our story, and we're stickin' to it!
But what a ride it is! Imagine hunting down the nastiest backroads you can find, with the knowl edge that there isn't a bump, pothole or spiteful set of curves you need fear. Goosing the throttle between a pair of second-gear switchbacks floats the front wheel with ease, while enginebraking, along with a bit of rear brake on downshifts, produces exhil arating, back-'er-in corner entries. Be forewarned, however, enough of these Sunday shenanigans and you may just get the urge to take your act to the track.
Which, as you know, we did. And with a fair degree of success, too. Against a mixed field of 250cc two strokes and 400cc four-strokes, I
snatched top honors in Middleweight Supermotard at Buttonwillow, with a repeat performance at another SuperlT in Portland, Oregon. Our 400 proved fairly competitive in the Open class, as well, particularly when pitted against purpose-built dirt-track bikes on a rough and bumpy track. The short, firmly suspended DT bikes would headshake like mad across the same bumps the WR soaked up with ease.
On the flip side of the same token, the WR feels tall and topheavy when ridden on a groomed dirt oval. It lacks the neutral han dling and forgiving nature of a well-setup dirt-tracker, and can be difficult to save once it slips too far out from under its rider. Fitting a set of gummie Dunlop KiSO dirt-track tires offered im proved grip and handling on a cushion track, but it’s clear that more than tires alone are required to make the WR behave like a real tracker. Such is the trade-off in versatility. Still, while serious flattrackers need not apply, a broadfocused bike makes good sense for the amateur-level racer who’s in it just for fun.
SUPPLIERS
Dunlop Tire Corp Box 1109 Buffalo, NY 14240 716/639-5200 Ki 80F front: $125 (110/90-19) K180 rear: $145 (120/80-18)
Gaiter Brakes USA 5788 Dawson Ave. Goleta, CA 93117 800/685-6633 Front pads: $36
Pirelli Motorcycle Tire 410 Eagleview Blvd., Ste. 106 Exton, PA 19341 610/458-9662 MT6O front: $119 (100/90-19) MT6O rear: $127 (120/80-18)
White Brothers 24845 Corbit Place Yorba Linda, CA 92887 714/692-3404 Pro-Meg silencer: $350 Works headpipe: $130 Powerlilter: $24 Front-wheel assembly: $484 Rear-wheel assembly: $546 Motard front-brake kit: $435 Eibach fork springs: $80 Eibach shock spring: $90 Fork modification: $180 Shock modification: $178 WR400 dual-sport kit: $441 UFO rear fender: $39 UFO handguards: $59 Graphics kit: $50
Roadracing our WR on tighter tracks was a kick in the pants, too. Putting it to the test, I took an Open Singles class win at a CMRRA road-
race at the Streets of Willow Springs. Sure, had there been a skilled rider on, say, a Ducati Supermono or Wood-Rotax roadracer in the field, the results might have been different. But win or lose, the fun factor would’ve been unchanged.
Exploring new ways to have fun on two wheels is the true essence of our Project WR400. Why be confined to a certain niche when you can cross several boundaries on a single machine?
