[ The wheelie is the enemy! A long wheelbase helped keep the front end of the Attack Performance MotoGP entry down at Indy. ]
The MotoGP CRT entry built by Attack Performance and ridden by Steve Rapp failed to qualify for the Red Bull U.S. Grand Prix at Mazda Raceway Laguna Seca this past July. But the team impressed many by not only qualifying but finishing 14th three weeks later at Indianapolis Motor Speedway.
Attack Performance’s Richard Stanboli said later that he had underestimated the difficulty for a rider in adapting quickly, not only to MotoGP’s Bridgestone tires and carbon brakes, but also to the lightness and higher performance of the Attack chassis and heavily modified, higher-revving Kawasaki ZX-10R engine. We can hope to see this team compete in MotoGP at least once more this season.
Two tests took place between the two races—one at California Speedway, the other at Indianapolis—allowing more basic parameters to be moved toward their optima. One was wheelbase. On the Indianapolis track, with its twisting infield, a long wheelbase proved best. Another was fork spring rate, which started out at .85 kilograms per millimeter but moved up to .95, indicating Rapp was getting to terms with the extra power of carbon brakes. The harder you brake, the more support the bike needs from the fork. Another change, coming later, was raising of the swingarm pivot to its highest position, increasing rear anti-squat and boosting mechanical grip. Changes eat time.
After about 10 laps of Friday morning practice, with the engine using a World Superbike-like redline of 15,000 rpm, a rod bearing gave up. The only cause that could be found was that the revs were too high for the hardness of the bearing material, which had been squeezed out the sides of the rod.
[ The Kawasaki engine came out after Friday practice to replace a damaged connecting-rod bearing. ]
Rapp said, “The bike started slowing down into Turn 1, and then the engine locked up.”
Although a lesser-spec AMA SuperBike engine was ready in the truck, Rapp asked that the damaged engine be rebuilt to keep the extra performance built into its better cylinder head. The team worked late, having the titanium rods resized at a local race-engine shop, then building the engine back up with a heavier stock crank and replacing it in the chassis. With rev limiter reset to 14,500, the engine ran faultlessly through practice and race. The work was done, and it was good work.
Did the heavier crank slow the bike down? No, in fact, Rapp said, it “mellowed everything out.”
This time, qualifying was no problem, showing that speed had been gained. In the race, Rapp ran mostly 1:43s to leader Pedrosa’s 1:39s. This was a four-percent difference, considerably smaller than the 107 percent of pole required to qualify. The highest-finishing CRT bike was the Kawasaki-powered Avintia Blusens BQR of Yonny Hernandez in ninth, lapping at 1:41s and 1:42s and timed at a best of 195 mph. Veteran Colin Edwards, one place ahead of Rapp on a BMW/Suter CRT, ran laps that were about two-thirds 1:42s and one-third 1:43s.
Rapp, who says this is “the best bike I’ve ever ridden,” has not come as far as he can in adapting to the Attack Performance machine. If I were him, I’d be wondering where I’d be now had I been active in the series since the season began.
[ Steve Rapp at speed on the Attack Peformance CRT entry. ]
