Suspension Animation
Life and Times of a Track Mule: Part 1
Mark Gardiner is preparing a Kawasaki ZX-6RR for an assault on the Northwest 200. The first step was to sort the suspension, with assistance from Race Tech.
Story and Photos by Mark Gardiner

Modern sport bikes handle very well in stock trim. That’s a fact. In recent years, however, sport-bike geometry has pushed the stability envelope—to the point where even some top-level racers started asking for more predictability, whether it came at the expense of flickability or not.

Sport-bike suspension has also recently become stiffer, in order to control brake dive and acceleration squat—fine for a billiard table-smooth race track, but too harsh for real roads, where 90 percent of us do 90 percent of our riding.

In cahoots with Road Racer X and Falkner/Livingston Racing, I’ve taken on a long-term Kawasaki ZX-6RR. Although it will spend most of its life on racetracks, my own long-term plans include a return to the British Isles for some real-roads racing. For max speeds under all conditions, the first step is obvious: Take it to an ace suspension tuner.

After uncrating the RR and giving it a token break-in, I took it out for my traditional baseline ride—over Mount Palomar. Up the technical, seven-mile Palomar South Grade road, it was very stable and predictable. Down the faster and bumpier East Grade, it bounced me around in the saddle, though it kept its line even when those bumps came in mid-corner. The only waggle of the ‘bars came when climbing, accelerating, and turning were all combined with a cattle guard. A perfect challenge for Race Tech (www.racetech.com)—I mean, Paul Thede can obviously make a bad bike handle better, but could he take an already excellent bike and make it handle better?

Surprise #1: the shock itself would be re-valved and re-sprung instead of replaced. “Why throw out the stock shock?” Thede asked, but it was a rhetorical question. “In the old days, sport-bike shocks weren’t rebuildable, so for years the theory was that you’d buy a new bike and immediately spend $1,200 or more on a Penske or Ohlins. The thing is, now we can rebuild them, and the quality of stock components (for 2005, the Kawasaki comes with Showa) is such that as raw material, they’re as good as the aftermarket stuff. The only thing they lack is easy ride-height adjustment, but if you get the initial setup right, you can basically set it and forget it.”

Design Engineer Phong Diep specified a shim stack that should allow for lots of adjustability while still providing more than stock compression damping if I need it. Then, he selected a softer Eibach spring (8 Kg/mm, down from a stock 9 Kg/mm) to suit my weight.

My fork tech was Louie Martinez. “With me, it’s all about being clean,” he told me. While Louie was reassembling my forks, though, Diep second-guessed himself and came into the work area with a subtle change to the bump damping that would give me slightly more stiffness in high-speed compression.

Then, Paul Thede himself came down to the shop and asked what changes were planned for the fork’s rebound damping. The atmosphere in the clean room is pretty laid-back, but it’s still obvious that every employee feels Thede’s the authority. “Uh, we thought the rebound was okay,” Diep said quietly.

In fact, the rebound mechanism didn’t meet Thede’s approval. A midvalve (a second-stage damper that, along with the rebound stack, controls flow from the fork’s upper chamber to the lower one) was removed altogether. “All they do is create cavitation,” the boss said dismissively. Thede’s theory on rebound is pretty simple: He wants the tire in contact with the ground as much as possible. In extensive testing, he’s found that as rebound gets quicker, most riders’ confidence—their feeling of control—peaks before the point of max traction. “What I try and do,” says Thede, “is bring those two points closer together.”

With the suspension back on the bike, it was pushed into the Computrack area for an initial measurement. It was pretty straight, a testament to Kawi’s build quality. Computrack chassis optimization involves adjusting rake, trail, swingarm angles, etc., to a set of trade-secret “sweet numbers.”

To give you an idea of the extent of the recommended changes, the ZX-6RR came in with a rake and trail of 26.5 degrees and 118 mm. “I can’t tell you what I changed them to,” Thede apologized, “or [GMD Computrack boss] Greg MacDonald will kill me.” Still, I could see enough to get a good idea; Thede moved the forks very noticeably in the clamps, and raised the rear end of the bike with two thick spacers on the upper shock mount. Was I pretty sure it would turn on a dime? Absolutely. But what price would I pay in stability?

The final stage of the process was setting suspension sag. Thede targets 30-35 mm of race sag, meaning sag with the weight of the rider in place. He doesn’t worry about the ratio of free sag (sag under the weight of the machine only) to race sag.

By the time I took back possession of the machine, the fork and shock had been re-valved and re-sprung; the chassis had been measured and the geometry optimized. Depending on the exact machine and individual rider’s needs, the total cost of this service would range from $1,250-$1,700, hardly more than the cost of a top-quality aftermarket shock.

I purposely did not fit a steering damper before taking the bike back to my secret Palomar test facility. Turn-in, as expected, was easier. The machine seemed fairly willing to tighten its line, and the front tire felt planted. The suspension felt softer on harsh bumps, without undue brake dive. It hooked up well under acceleration. Despite the nominally more radical geometry, our RR felt, if anything, even more stable.

For all I could determine on public roads (with the stock—excellent—BT014 ‘stones) the revised handling was a win-win-win situation, with more compliance over bumps, easier turn-in, and even more stability—especially getting on the gas. Next steps: sticky buns, and a racetrack....