by Kevin Duke

Runnin' With The Devil

Aluminum frames, fuel injection and computer-assisted ECUs have all contributed to making sportbikes the amazing machines they have become. But perhaps the biggest influence in extracting max performance out of a modern sportbike is modern radial rubber.

As sportbikes keep getting more track-oriented, tire companies have been cranking out sticky street-legal buns that offer more grip than a regular sport tire for occasional track days while providing a larger temperature envelope and more durability than pure race rubber. In this class of tire, Dunlop has its D208, Bridgestone its BT010 and BT012, Michelin its Pilot Sport and Metzeler its Sportec M-1.

Each of the above tires have more grip than most riders have skill, and picking the one tire that stands clearly above the others is virtually impossible unless countless back-to-back comparisons are made on several different bikes, accommodating for the slight but significant variances in the sizes of each tire.

In lieu of that, let’s just say that Pirelli’s new Diablo Corsa series stacks up with the best of them, as we found out during a devilish ride on a deserted California backroad and while lapping Buttonwillow Raceway on three different bikes (not at the same time, silly).

In an effort to better understand its American customers, Pirelli has undertaken its first-ever large consumer study in the U.S. The results showed some persistent myths about Pirelli, of which the PR flacks at the Diablo intro were keen to try to dispel.

According to the survey, the perception of the brand’s strengths were passion, performance and cars, while the weaknesses included inconsistency, lack of product range, a lack of innovation, and a perceived high price. The perception of Pirelli’s inconsistency irked the Italian company, and it notes that it averages just one tire returned for every 1,000 it sells. That 0.12% return rate is far lower than the 2.0% industry average of 20 per 1000.

And, although Dunlop dominates the American motorcycle tire market and AMA racing, Pirelli is making huge inroads. Fabien Foret rode Pirellis to the World Supersport championship in 2002, and the Italian rubber was under the podium winners in all six major Isle of Man TT races this year. Pirelli also scored Formula USA championships in Sportbike and Unlimited Superbike this year, as well as the 2001-02 World Motocross championships.

Well-informed readers know that Pirelli and Metzeler joined forces a few years ago, a union that created a crowded tire lineup for the duo. The Diablo has the same mission as Metzeler’s Sportec M-1, but Pirelli was careful not to divulge the differences between it and the Diablo. Pirelli, naturally, said its tire is better than the successful Sportec in certain areas but wouldn’t specify which.

To better differentiate the two brands in the future, we can expect Pirelli to be marketed more toward the sporting side of motorcycle tires, while Metzeler will edge closer to the cruiser and touring riders who love high-mileage tires, according to Pirelli brass.

The Diablo line replaces the long-in-tooth Pirelli MTR21/22 Evo. Key among the Diablo’s design features is Ideal Contour Shaping (ICS) on its mid-crown section, a gradual curved section (rather than multi-radius tires of other brands). Pirelli says this results in more neutral, quicker steering and better side grip on its edges. And, while all tires should be the same brand front to rear, Pirelli says that if the Diablo’s front and rear tires aren’t matched to each other their full benefits won’t be realized.

DOT-approved race rubber, like Pirelli’s excellent Supercorsa we tested at the Ducati 999 press launch, is still the only way to go for competition bikes. But stiff carcasses, a narrower (higher) operating temperature range, and a lack of wet grip make them inadvisable for a street rider. Silica is the latest ingredient to expanding a tire’s temperature envelope, and Pirelli claims that its new silica compound offers “significantly” improved warm-up time. Well, warm-up is a bit of a misnomer, because Pirelli says that it doesn’t simply warm up faster, but rather its temperature envelope has been stretched so that it reaches the operating temperature range earlier.

For wet conditions, the Diablo’s front tire is heavily treaded to disperse standing water. The central area of the rear tire has few treads so the rubber doesn’t deform much under load, but wet-weather riders needn’t worry because Pirelli says the front tire clears the water for the rear.

Pirelli uses its patented 0-degree steel-belt construction in the front and rears. Most other brands use a Kevlar-type aramid fiber to hold the tire together, but Pirelli says its tires don’t weigh more than other brands because the steel belts can be so thin.

Pirelli also uses its patented “PenTec” in its front tire, a fiber made of naphtalate polyethylene (rather than nylon or rayon typically used). Pirelli claims it is 10-times as strong (so the tire can be made lighter) and is much more elastic and flexible. The front Diablo, and indeed all brand’s tires, needs two-plies because its stability is paramount each time the tire is under stress, such as when braking and turning. But because the rear tire has one ply, using PenTec is not that big an improvement for the extra cost to use the material so it is only Pirelli race tires (in which light weight is more critical) that use PenTec in the rear rubber.

Throughout the tech briefing, Pirelli made several mentions about the tire’s forgiving nature and their predictability. “The tire should talk to its rider,” said R&D chief Cagatay Saygili, adding that, “it’s an intense time of development” for Pirelli.

To put these theories to the test, Pirelli sent us off on one of my favorite California roads, Highway 58 headed east out of Santa Maria. This two-laner has a bit of everything, from pastoral rural towns to flat stretches of lightly-patrolled straightaways, which lead to twisty canyons and an awesome roller-coaster section that can induce 100-mph air time.

As fun as 58 is, it’s unwise to completely push a tire’s limits on public highways. Fortunately for us motojournos, Buttonwillow Raceway sits at the end of the road.

Pirelli suggests some surprisingly high pressures to run in the Diablo, even for track-day fun. It recommends 32 psi in the front and 39 in the rear, and Pirelli says extra tire life on the street can be had by running 36 in the front and 42 in the rear.

My mount for the bulk of the day was a Triumph Speed Triple, a streetfighter-styled bike that has a howling midrange and light-effort steering. The Diablos, unlike some race-compound tires, are available in a 190-section rear tire to match the buns fitted at the factory.

Soon after I got accustomed to the east loop circuit, the Diablos gave me the confidence to reach their edges and scuff the relatively high-mounted pegs. The bike exhibited neutral steering characteristics, even with the big 190 on the back rather than a 180 that makes many bikes steer sweeter. And when exiting slow corners, a rider can feel the rear tire dig in under the Triple’s big midrange pull.

The Diablos actually offer more grip than the Speed Triple’s chassis can handle. The tubular alloy frame may look trick, but its steering head can’t handle the combination of sticky tires and aggressive riding, as evidenced by the slow weave that accompanied every lap exiting the left-hander after the hill from around 80 mph to about 120. A mushy-feeling front brake that came back to the bar sealed the deal, and I set off in search of other toys.

Next up was a Kawasaki ZX-6R, a bike more suited to track work. The 2002 ZX has a comfortable riding position for a Supersport bike, a quality that many street riders are going to miss on the ultra-racy 2003 ZX. The old girl is actually fairly competent getting around a racetrack, with a secure feeling chassis that encourages high corner speeds. The Diablos showed excellent stability when really pushed hard, and they transmit clear signals to the rider that made them predictable.

A lonely Honda CBR600F4i sat unwanted in the pits, and the ambient temperature of the rear tire offered the test to see how quickly the Diablos got sticky. I rode the first part of my out-lap gingerly, afraid to commit the dreaded crash-on-cold-tires trick. But even before I got through my out-lap, the tires gave me enough confidence to drag my knee.

The CBR feels much smaller than the ZX, with better brakes, quicker steering and a significant amount of extra power. This excursion reminded me of how good the F4i is on the track, something Honda buyers will want to keep in mind before shelling out the $8,600 for the new RR version; the F4i continues in production with an MSRP of $8,199.

The Diablos continued to impress. Just lay the bike in on its peg feelers and scrape your way around the entire corner. The tires offer loads of grip, enough to ensure metal shrapnel even without the hero blobs. Laps were clicked off in less time and, even at this increased pace, the Diablos proved their excellent stability, especially under braking and in high-speed corners. Tires that are stable run the risk of being constructed too stiff, but the Diablos tracked through bumpy corners without drama.

I stayed on the CBR until the low fuel light began to annoy me, while the Diablos remained consistent and predictable, with almost no drop-off in grip through the 40-minute session.

I logged a few hundred more street miles with the Diablos on the Speed Triple, and I continued to be impressed at how much traction the rear offered under hard acceleration on cold (well, as cold as it gets in SoCal, about 50 degrees) pavement.

The Diablos come in an array of sizes to fit most any sportbike on 17-inch wheels, including a 200-series rear and a 110/70 front. And don’t toss that old CBR900RR, because Pirelli also makes a 130/70-16 to fit the failed Honda experiment that used a 16-inch front wheel. Pirelli says Diablos will be priced within 2-5% of its competitors and should be at dealers early in the new year.

The bottom line: I wouldn’t hesitate to recommend the new Diablo Corsa to any sportbike owner. Metzeler’s Sportec was among our faves among this type of tire, and the new Pirelli is at least its equal.