Team Cycle World Attack Performance spent two days last week at Buttonwillow Raceway testing its 2011 Kawasaki ZX-10R AMA Pro American SuperBike and ZX-6R Daytona SportBike. Veteran racer Eric Bostrom and team newcomer JD Beach each completed more than 100 laps around the bumpy, 2.7-mile Central California racetrack.
This was the third time Bostrom had ridden the all-new 10R that he will debut at the AMA season opener at Daytona next month. Bostrom participated in the Dunlop tire test at the recently repaved Florida track in mid-January and later that same month signed up for three classes—A Superbike Expert, Formula 1 Expert and Heavyweight Solo 20 Expert—at a WERA West race weekend at Las Vegas Motor Speedway. Beach had ridden the ZX-6R just once before—at Daytona during the aforementioned tire test.
Bostrom struggled to breathe freely on the first day of the Buttonwillow test. He’d crashed his motocross bike one week earlier, and his ribs were still sore from the resulting impact. Despite being in obvious pain, Bostrom was typically upbeat. “I’m so mad at that dirtbike,” he joked. “How many days do we get a racetrack all to ourselves?”
Due to the last-minute nature of the program, the ZX-10R’s engine was still stock, though MoTeC electronics and a World Superbike-spec 4-into-1 titanium LeoVince exhaust were in place. Crew chief Richard Stanboli explained that the chassis and, to a lesser degree, electronics, were the focus of the test. Chassis imbalance stemming from soft rear suspension had given Bostrom fits at both Daytona and Las Vegas.
Bostrom hadn’t seen Buttonwillow for 10 years. After a few sighting laps, he pulled into the pit. Even using Daytona gearing, Bostrom wasn’t able to get out of third gear. “It looks like a full-size racetrack,” he said. “But on the ZX-10R, it feels like a go-kart track. Can’t let the big dog eat!”
Öhlins Road Race Manager Mike Fitzgerald flew to California from the Swedish suspension company’s North Carolina U.S. headquarters to provide additional support for the team. “Streetbikes are so safe and stable,” he said, “you could trim your nails in the middle of a corner. We need to raise this bike to give it more agility, to make it more edgy.”
Fitzgerald began by adding several shims to the frame clevis, increasing rear ride height significantly. Bostrom liked the change. “Big, big difference,” he said. “The bike is much less prone to wheelie. The front end was a ghost before; now, it’s more planted. But we’re lacking accuracy. We have lots of weight transfer—way too much suspension movement. It’s like a rocking chair that’s always in constant movement.”
Fitzgerald then installed firmer springs and increased compression damping at both ends of the motorcycle. A series of bumps at the exit of Turn 2 had sent the bike into what Bostrom later described as an “instant tank-slapper.” He returned to pit lane with wide eyes. “It’s a freakin’ handful,” he told Beach.
Fork offset was reduced from 28mm to 25, and Bostrom immediately dropped 2 seconds per lap. “I can’t believe how much stability we gained,” he exclaimed. With renewed confidence in the bike, he was able to add mid-corner speed and explore edge grip. “The faster I go, the better it is,” he said.
Stanboli and Fitzgerald continued to chip away at a base setup. “We’re going to end up where I would have liked to have left the shop,” said Fitzgerald, “but Eric probably wouldn’t have been ready for that.”
Stanboli had installed an upgraded MoTeC dash, which looks very similar to the unit that the team used last year on its Suzuki GSX-R1000 but has more functions, downloads faster and has advanced-math capability. Stanboli also hired Sander Donkers, previously with American Honda and Pat Clark Motorsports, to help with electronics, which are unrestricted in the American SuperBike class.
Donkers acknowledged that the ZX-10R’s stock wheelie control performs well. At Buttonwillow, the MoTeC version required fine-tuning. In the morning, we watched as Bostrom, the toe of his right boot planted firmly on the rear brake pedal, wheelied off the final corner of the track. Partway down the front straight, the front end of the bike was still “porpoising” up and down. “The bike knows that it’s wheelying,” said Donkers. “It just doesn’t know how much it is wheelying.” By the afternoon, more control was in place. For the most part, the front tire just skimmed the pavement as the bike accelerated past the team’s pit located midway down the front straight.
Fitzgerald continued to experiment throughout the afternoon. He and Stanboli eventually concluded that the rear suspension linkage appears to be a critical aspect of the ZX-10R, whose shock is almost horizontal, allegedly, to help keep it cool. Later that night, Stanboli received an e-mail from Kawasaki’s World Superbike team that included dimensions for a new linkage. Ironically, one of the goals was to increase weight transfer. “We’ve got plenty of transfer,” laughed Stanboli.
With progress stalled at the rear, the team turned its focus to the front of the motorcycle. By mid-morning, Bostrom was lapping 1.5 seconds quicker than he had the previous afternoon. “I’m having trouble keeping the front end planted through the bumps and dips,” he said.
Fitzgerald methodically tried one option after another—springs, damping, preload. At 4 p.m., Bostrom pulled in and flipped up his faceshield. “That’s a really good front-end setting,” he said. “It’s firmer, with more feedback and control. I can ride with more aggression. I think we’re at a wrap point.”
Tire wear was remarkably good throughout the test. Stanboli brought a load of American SuperBike-spec 17-inch Dunlop slicks, but mechanics Jim Matter and Todd Fenton only changed tires once—and Bostrom had begun the test on scuffs from the Las Vegas race weekend! By end of the second day of testing, Bostrom had completed 58 laps on the front and 54 laps on the rear.
With so much attention focused on Bostrom, Beach quietly pounded out laps. The Washington State native had never ridden at Buttonwillow, but he quickly posted competitive times. Kawasaki’s Joey Lombardo had worked with Beach at both Daytona and Buttonwillow. “He’s intelligent and communicates well,” said Lombardo.
At the tail end of the test, Bostrom made a few laps on Beach’s 600. The 2001 AMA Supersport champion will also ride a ZX-6R in the Daytona 200. As Bostrom roared away, Beach turned his gaze to Bostrom’s SuperBike.
“No,” said Stanboli. “After Daytona. Maybe.”
“I’m going to hold you to that,” smiled Beach.
I asked Stanboli how he felt the test went for the team. “It was a good test,” he replied. “We learned a lot about the character of the motorcycle and tried a lot of different things. Now, we know what our plan will be going into the next test.
“We made quite a few damping changes trying to control weight transfer and the geometry of the motorcycle in stock form. We’ll have one, maybe two, new linkages for the next test. I’m fairly certain we’ll have a built engine, as well. We learned a lot. And so did the rider.”
The next test is scheduled for February 21-22 at Chuckwalla Raceway near Palm Springs, California.