MD Product Evaluation: Pirelli Diablo Rosso

By Willy Ivins
Photos by Kevin Wing and Andrea Wilson

Santa Paula, California, the site of Pirelli's unveiling of its latest update to its staple product, the Diablo is a quiet town just about 17 miles southeast of Ojai. It is 1 ½ hour ride from the fastest road in the west, Willow Springs Raceway, where I spent the day getting reacquainted with my 125 GP bike.

Sore and tired (but smiling), I bring my street bike to a stop in the back parking lot of the quaint Inn that Pirelli has arranged for the invited press to stay at, where a waiting Pirelli crew whisks away my bike to install its new shoes, the new Diablo Rosso. Some liquids, a shower and I am refreshed in time for the tech briefing of the tire I'll be riding tomorrow.

From a sales and marketing perspective, the Rosso is a very important product for Pirelli. Aimed at no particular segment, it is designed with supersport (e.g., 600s and 1000s), sport-touring, UJM (think Suzuki Bandit), and supermoto bikes in mind. That said, the supersport class carries significant sales weight in the overall design/development picture. Pirelli has enjoyed double-digit sales improvement in previous years and claims an 87% increase in 2007 alone, so the importance of this tire becomes quite clear.

A 5-year development cycle has brought the Rosso to fruition, with careful attention being paid to the evolution of the bikes we ride. Greater power and torque, lighter weight (up until last year) coupled with more rigid chassis and slipper clutches had placed different and unique demands on a tire.

To tell us about their new pride and joy, Pirelli had not only their North American contingent, but also the Italian engineers who are responsible for the Rosso's performance. They are a passionate bunch who cover the miles and drag their knees through the corners just as we do.

The foundation of Pirelli's development of the Rosso is a trio of acronyms, including Enhanced Patch Technology (EPT), coordinated with Functional Groove Design (FGD), and Ideal Contour Shaping (ICS), the latter being developed for the original Diablo that uses both computer simulations and test rider feedback.

What's different? Plenty. Let's start with the tread pattern. Markedly different in appearance to the Diablo, the pattern is a result of what Pirelli calls "Functional Groove Design", which puts grooves where they'd be most useful in the rain - for the all-weather riders out there, and fewer where the tire can deliver maximum traction when the roads are dry. The front tire has the duty of clearing a dry(ish) line in the wet, and so has more grooves overall, which reach the edge for the wet stuff. Looking at the back tire, the land/sea ratio is noticeably higher with a solid rubber edge telling the observer that Pirelli is looking to get as much rubber to the road when it counts most - when you're on the edge.

Under that tread pattern is a zero-degree steel belt to help maintain proper profile shape, elasticity for progressive feedback and stability under hard braking. The tire structure is also designed to ensure that the front and rear tires work together in a balanced manner.

Rubber compounds are new, and unique in regards to front and rear applications. The rear tire has a balance of rigidity and hysteresis - the flex of the rubber that allows it to conform to the texture of the pavement - for both high and low temperatures for a fast warmup and a linear grip response. Silica black, carbon and high mechanical resistance chemicals combine to create a tire that has strong traction, even wear and exceptional traction in the wet. The front tire has higher hysteresis materials with a high energy dissipation factor (good bump absorption) for more grip and high braking stability. Silica and carbon black make their appearance here as well for wet weather grip.

Another issue concerning wear rates was addressed by the Rosso design team. Typically, a front tire will handily outlast the rear tire, forcing the rider into a dilemma of whether to fit a new rear tire with a partially worn front, or spring for a new front tire to replace it as well. Pirelli says that the front and rear Rossos should wear relatively evenly. Does this mean the front wears more quickly? Actually, no. The rear tire is intended to last more like the front tire, which is good news.

After the technical presentation, we were whisked off to Ventura for a tasty dinner. During the 30 minute ride, it became known to me that we were accompanied by Steve Rapp, 2007 Daytona 200 winner (on Pirelli, naturally), his crew chief and Attack Kawasaki team owner Richard Stanboli, Chris Kilmore, the DJ (or turntablelist) of Incubus and Chris Heese, the drummer of Hoobastank. Pirelli has a marquee following, or the lure of free food, tires and a track day was too much for them (Steve Rapp excluded) to resist! Okay, I admit, I went for the tires and track day………

Since the Diablo Rosso is intended to be a high performance street tire, part of our day testing them would be spent navigating the local canyons leading out to the Streets of Willow Springs. Highways 150, 33, Lockwood Valley Route 138 and a gnarly, narrow, dirty stretch of pavement with plenty of blind, decreasing radius corners with not so much as a centerline painted on it were on the morning ride menu. Just to prove their point about the tires working on a multitude of different bikes, there were also a number of alternate motorcycles available for our use, such as the Ducati Hypermotard, Triumph 675, GSX-R1000, Buell and BMW Boxer, etc. Because I am testing tires and familiar with my own motorcycle and its setup, I did not partake in the other bikes available to make sure I did not muddy the feedback with the feel of an unfamiliar motorcycle. I sure was tempted to grab the Hypermotard, though! So, what are the tires like? Very, very good. They're another step toward the ideal sport tire.

The weather could not have been better. Dry, cool (60s) with a slight breeze in the morning, with temps rising to 70 or so in the afternoon, without the dreaded wind tunnel treatment the Willow Springs Raceway complex usually features. Road conditions were similarly favorable, but street riding always has a level of unpredictability with its gravel, water crossings, patches of sand, etc. In other words, it is a perfect venue in which to test the claims of the Pirelli Rosso. Although temps were mild, The Rabbits of the group (I tagged along with them) wasted no time testing the quick warmup (unscrubbed as well) portion of the claims and found they indeed performed well while coming up to temperature. Tire pressures were set at 32 front, 36 rear for all motorcycles. The aforementioned highways and roads provided all the expected challenges with a couple water crossings thrown in for good measure.

The unnamed, gnarly little road that provided a welcome roller coaster sidebar from route 138 perfectly showcased the front Rosso's capabilities. Elevation changes followed by downhill, decreasing radius, blind corners (did I mention the patches of sand?) placed a premium on steering quickness, braking stability and neutral behavior on the brakes if I was to stay in tow of The Rabbits. Need to scrub speed into the decreasing radius turn? No problem, just give the lever a light pull. Is there sand on your chosen line? Line changes are part of the Rosso's game. I don't remember a truly straight stretch of pavement on this portion of the ride and yet any difficulty in changing direction never registered in my data banks. One item that did register with me was the word confidence. The front tire always felt planted and gave great feedback, so I did not feel nervous or tenuous while following The Rabbits. What about the rear tire? It performed well, but it was not challenged like the front tire was. Its time would come at The Streets of Willow Springs.

After arriving at The Streets, we all ate lunch, and then started our sessions on the 1.8 mile course, and The Rabbits became Cheetahs. Again, warmup presented no problems and we could very quickly get down to business. OE suspension was considered during development of the Rosso, but full aftermarket suspension on our bike meant we could not assess their claim. Nonetheless, this track provided a severe test of the tires' ability to deal with the heavy braking, cornering and acceleration loads (that should be) only experienced on the track.

Turns two and three challenge the front tire with heavy braking loads on corner entry and the Rosso never flinched. The bowl turn at the back end of the course is significantly banked and provides an opportunity to heavily load the suspension and tires with a double whammy of corner speed and hard acceleration. After the back straight, a short, bumpy, 'S' complex sees the rider carry fairly high speed through it while on the brakes over a slight rise. The front behaved here as it did on the street - that is it gave me confidence and great feedback. The myriad of other bumps and pavement changes were handled with equal aplomb.

Our GSX-R750's relatively modest power (compared to the GSX-R1000s in attendance) output did not start to overcome the back tire until the fourth session. This was not due so much to a deterioration of the tire performance as it was my continuing to push harder to find the limit. A small slide here and there let me know I was toeing the line. My pace was a front running 'A' group rider at a track day, but not race pace. Keep in mind that tire pressures were never lowered. The Cheetahs on the 1000s experienced this problem to a much greater degree, and while the issue was alleviated somewhat by lowering the rear pressure to 31 psi, the problem never went completely away. I may not have had the occasional slide with slightly lower rear tire pressure.

While our bike is well suspended, the footpegs are set in the lower, forward position. Lean angles were enough to scrape the shift lever and in the last session, bend back the brake pedal. That speaks well of the Rossos.

I overheard some grumblings about the pavement condition, i.e. bumpy, inconsistent, etc. While I admit that The Streets is far from being a Barber Motorsports Park, I feel it did provide a relevant test of the Rossos. Not many public streets out there have the surface quality of the Alabama track. I wondered out loud about how the Rosso would do on the big track and was answered by Salvo Pennisi, the Pirelli testing department manager. He said that the big track, despite its higher speeds does not as severely test a tire because the turns are more open and flowing, which does not place a premium on acceleration, turning and braking loads, whereas the Streets' turns are the opposite characteristic.

The Rosso is going to replace the current Diablo, and it definitely raises the bar. Although marketed as a street tire, it acquitted itself well on the track.

Pirelli is definitely on a roll after stepping up to be the sole supplier for the World Superbike series in 2004. A spec tire class was supposed to spell the end of tire development, according to the naysayers. Quite the opposite has happened. Pirelli has gone full speed to constantly develop products that surpass whatever came before it and then made it available to anyone. As of this writing Pirelli has been named as supplier of the ultra competitive British Superbike Series.