From the May 2016 Print Issue Of Roadracing World & Motorcycle Technology. Copyright 2016, Roadracing World Publishing, Inc. used with permission. Visit www.roadracingworld.com to subscribe.
ON THE TRACK
Bridgestone S21 front and rear tires.
Yas Marina Circuit
Abu Dhabi, United Arab Emirates
BUILDING A BETTER BRIDGESTONE
By Chris Ulrich
Bridgestone’s motorcycle tire lineup has to be the best kept secret in the United States. I was impressed after riding on Bridgestone’s Battlax R10 DOT and V02 slick racing tires at the world press launches for the Yamaha YZF-R1 and Kawasaki ZX-10R, yet the brand doesn’t have as strong a presence as its competitors in the high-performance streetbike tire market.
During the YZF-R1 launch at Eastern Creek in Australia early last year, I was able to turn my best lap of the day on a set of Battlax VO2 slick tires with 75 laps on them, with no drama. The Battlax V02 racing slicks are directly descended from Bridgestone’s MotoGP racing program; the front and rear tires both use the GP tire’s triple-belt construction, adding a Kevlar belt to the standard zero-degree steel belt and the standard Kevlar belt. The additional Kevlar belt helps keep the tires from deflecting under heavy load, adding stability. The triple-belt design also allows the Bridgestone slicks to run relatively low tire pressures, increasing the size of the contact patch and adding grip. (Bridgestone’s DOT-labeled Battlax R10 racing tire is also fast and durable with great feel.)
Now that it has ended its run as the exclusive spec tire for MotoGP, Bridgestone is working on applying what it learned and using the advanced technology it developed to improve the performance of the tires it sells to consumers.
Bridgestone chose the Yas Marina Circuit in Abu Dhabi as the venue for introducing its new S21 hypersport tires. Motojournalists and invited retailers rode from dusk to midnight on the F1 racetrack.
The 2016 Bridgestone Battlax S21, which supersedes the S20 EVO, is the latest hypersport-category tire to be introduced by the Japanese tire giant. The S21 has ties to Bridgestone’s MotoGP project as it is the first road-going tire to be developed using the Ultimate Eye, an indoor testing facility that allows engineers to simulate real world riding conditions in a controlled environment. In simple terms, the Ultimate Eye is a dyno for motorcycle tires.
The new S21 front tire features a new profile that is more triangulated and wider at the edges to increase the size of the contact patch at high lean angles, while reducing the size of the contact patch (and friction) when riding in a straight line. The three-layer compound places a durable compound in the center and a softer high-performance compound on the shoulders for better cornering performance. The area around the bead has also been slightly stiffened up to increase stability.
Bridgestone engineers also revised the shape of the rear tire, and moved the tire grooves closer to the center of the tire to increase the contact patch area at full lean without sacrificing wet weather performance. The wider rear tire features a five-layer compound with the harder compound in the center, a slightly softer compound between the center and the shoulders, and a higher performance compound placed at the shoulders to optimize grip when fully leaned over.
Bridgestone engineers claim the changes improve durability and performance over the life of the tire when compared to the S20 EVO. One of the most interesting claims was a two-second reduction in lap time at the Sugo Circuit in Japan. Such a massive improvement in lap time on the racetrack shows Bridgestone’s intentions with the S21, even if it isn’t aimed specifically at the racing or even the track-riding segment of the replacement tire aftermarket.
Introducing a street tire focused and developed on the racetrack carries a risk since riding on the racetrack puts a lot of demands on a tire. But the rationale makes sense: Using the racetrack—instead of the street—provides a safer, more consistent environment to test the performance of the tire. Which is why Bridgestone invited a delegation of motojournalists to the Yas Marina Circuit in Abu Dhabi to sample the new Battlax S21 aboard a variety of motorcycles—including inline four-cylinder sportbikes, streetfighters, and V-Twins.
Ulrich testing the new S21 tires on a BMW S1000RR and Kawasaki ZX-10R on the track located in the United Arab Emirates.
After picking from a selection of the latest and greatest motorcycles on the market, we started lapping the Yas Marina Circuit at dusk and ran deep into the night under the floodlights. The condition of the track didn’t change much, but there is something very cool about ripping around an F1 circuit on a motorcycle at night.
I started the night on a 2016 Kawasaki ZX-10R, then moved to a BMW S1000R, a Honda CBR600RR, a BMW S1000RR, and finished the night on a Honda CBR1000RR SP. There was no time for suspension changes and the electronics settings were completely out of whack most of the time. Bridgestone had brought a bunch of retailers with varying skill levels to ride on the track along with journalists, so the power settings on the 1000s were turned way down. Fortunately I’d been to the press launches and knew how to change the ECU settings on the BMW and Kawasaki to restore full power! It took some fiddling around but I remembered how to change everything back, and got a great refresher course on how to adjust the electronics!
On The Racetrack
Overall performance of the Battlax S21 was impressive on the racetrack. The front tire has great braking stability in a straight line, but lacks some grip on the edge at full lean. This is typical of tires in the street segment—they just don’t adhere to the ground as well as a racing tire and have a tendency to push wide if you really lean on them. I experienced push on all of the 1000cc sportbikes I rode, including the ZX-10R, the S1000RR and the CBR1000RR SP.
The performance of the S21 front tire was a lot better on the lighter and less-powerful Honda CBR600RR. To my surprise, I reached the limit of the suspension settings—bottoming the forks—before reaching the limit of the front tire. Performance of the Battlax S21 front tire was also good
Colors show positioning of different compounds in S21 rear tire tread.
on the BMW S1000R—the less aggressive nature of the bike along with the upright seating position forced me to back the pace off enough that the limiting factor was the motorcycle rather than the front tire.
Which brings us to the Battlax S21 rear tire. As expected—and as is the case with the other tire brands in this segment—the rear tire could fully handle the power of a high-performance 1000cc sportbike for a handful of laps before tire slip increased during hard acceleration. Depending on the pace and the number of fast laps strung together, this point would come at around lap five or six in a run. Endurance may vary depending on the individual racetrack, bike settings and riding style, but this what I experienced at Yas Marina Circuit. The slide characteristics from new to worn are consistent; the S21 has great feel and feedback through the acceleration zone; and the connection between the throttle and rear tire was great no matter what brand or model motorcycle I was riding. The overall performance of the S21 rear tire would gradually drop off as the laps went on, but there wasn’t any sudden or dramatic decrease in performance.
Rear tire performance was significantly better on the Honda CBR600RR. It simply comes down to physics: The bike puts out less power and less force so the tires last longer than they would on a 1000cc motorcycle. It was the same story on the BMW S1000R—the forced reduced pace allowed the tires to deliver their full performance and grip longer.
Bridgestone brought a lot of tires and kept tire-changing machines busy during the nighttime S21 intro event at Yas Marina Circuit, in Abu Dhabi.
Testing the outright performance of street-oriented tires on the racetrack—where bikes are supposed to go fast—is a good thing. If tires can hold up on the racetrack, then they’re more than capable of performing on the street or in the canyons. The new Bridgestone S21 isn’t going to help anybody set new absolute track records, but it’s still capable of turning some very quick laps—and the tire is durable enough to use for most of the day on a 1000cc sportbike. Overall, the S21’s performance matches other tires in the segment, including the Dunlop Q3 and Pirelli Diablo Corsa Rosso. Which makes the Bridgestone Battlax S21 very competitive in the hypersport tire category, and well worth a look.