08/31/2020
Technical Data Episode 3: PirelliMoto Diablo NEW WSBK Slicks 125/70-17 and 200/65-17 compared to Diablo SBK Slicks 120/70-17 and 200/60-17
Test Rig: 2017 Suzuki GSXR-1000R , Öhlins USA FGRT forks, TTX GP rear shock, Steering Damper, Dymag Performance Wheels Carbon Wheels, Brembo Billet Master Cylinder, T-drive Rotors, GP4RX Calipers, Z04 pads, Attack Performance Zero offset clip-ons, rearsets, Yoshimura Research & Development of America, Inc. Full Ti race system, Case covers, Lightech Racing frame sliders, axles sliders, and chain adjuster, Drive Systems USA Inc. gearing, Chicken Hawk Racing Tire Warmers Professional Warmers, Pit Bull stands, Rieger-Rennsport Paddock Wizard.
Last year Pirelli introduced a now WSBK tire, the Diablo Superbike 125/70-17 and 200/65-17 slicks. This year it became available in NA to club racers and track enthusiasts. We spent a lot of time dissecting and comparing these tires to the previous 120/70-17 and 200/60-17 tires, which are still current and available. We hoped to bring you this data sooner this year but due to Covid, our testing plans were delayed. As with any testing, there is subjectivity and as an Engineer, we know to eliminate as many variables as possible. The actual hard measurements are not subjective, the numbers don’t lie. Note that these are ACTUAL mounted measurements we took, NOT from some datasheet or internet site. The rider’s opinion is a little more difficult to eliminate subjectivity. For our rider test, we conducted it in a single day at the same track with 2 sets of identical Dymag carbon wheels mounted up with the different rubber all baking at the same temps before we dropped them onto the test rig. We conducted the rider portion at a FastrackRiders Riders Event at Autoclub Speedway in Fontana, CA over the course of 1 day on 8/22/20.
The Numbers:
120/70-17 front slick Dia = 604mm , weighs 9lbs 7ozs, mounted horizontal width = 118mm, tread profile circumference from edge of sidewall to edge of sidewall = 72mm, sidewall height = 19mm
125/70-17 front slick Dia = 610mm, weighs 9lbs 11ozs, mounted horizontal width = 124mm, tread profile circumference from edge of sidewall to edge of sidewall = 70mm, sidewall height = 24.5mm
200/60-17 Rear slick Dia = 662mm, weighs 14lbs 15ozs, mounted horizontal width = 200mm, tread profile circumference from edge of sidewall to edge of sidewall = 254mm
200/65-17 Rear slice Dia = 673mm, weighs 15lbs 6ozs, mounted horizontal width = 200mm, tread profile circumference from edge of sidewall to edge of sidewall = 260mm
As you can see from the numbers, the new tires are simply taller, wider in the front with a major jump in sidewall height and different profile shape, and a little bit heavier (about 2.3% gain in weight, but still significantly lighter than the other Major US brand).
We did our ride test by just dropping the preheated tires onto the test rig with NO suspension mods. Same hot PSI between the tires. (in a future test, we will make suspension changes and conduct this test again). We did this to be able to answer the #1 question most riders will ask which is: “do I need to change my setup”. Just dropping the tires onto the bike, it will raise the bike from the axle to the ground 3mm in the front, and 5.5mm in the rear. This raises the CG overall, and pitches the rear up higher by 2.5mm relative to the front, decreasing rake and trail slightly.
Sitting on the bike in back to back sessions with the different tires mounted, you can feel the height difference immediately. The answer to the #1 question is in my opinion NO, you do NOT “need” to make setup changes and CAN just drop these tires on in “most” cases. If you are a racer, you will of course want to make changes as you are always chasing that elusive optimal setup, chasing those tenths 😉.
Rider impression of differences was surprisingly minimal. I expected the bike to steer a little quicker with the changed geometry, but it did not. I suspect the different profile of the front tire combined with the slight weight difference countered what would have been a slightly quicker steer geometry if you made those geometry changes on the same tires. The front tire did have a slightly different “feel” to it. A little hard to describe but I will make an analogy to the front feeling “softer” like as if you lowered the PSI or the carcass was more compliant while leaned over. It gave the rider a feeling of the front being more planted under trail braking but NOT over flexing/folding like with an under inflated tire would. I suspect the much taller sidewall (25% taller) of the 125 tire attributes to this feeling as sidewall flex/bump compliance would be increased with a taller sidewall, especially at high lean angles.
We did push the pace and noticed a few minor negative side effects. Under extreme hard braking from the high speeds down the back straight into T12, the rear end did get lighter and was a little less stable. This is expected as the increased height/CG and higher rear end bias vs front would have the bike unweight the rear end a little more and rotate more weight to the front under braking. This can be corrected by lowering the bike and changing the weight bias. The other thing we noticed was that the bike would run slightly wider under acceleration past the apex. We suspect this may be due to the front profile shape being not as “peaked”. We will discuss this in more detail in the next Tech writeup after we conduct this test again with suspension changes for each tire.
It is difficult to measure performance differences via lap times during a Track day due to traffic during the sessions as a variable that we cannot control so we have not compared/discussed those. In the next Tech writeup, we may compare those if we are confident we have unhindered laps.
At Friction Racing Products, we ride what we sell, and only sell what we ride and believe in. We provide our customers with data to make informed decisions and extract the optimal performance from your equipment.
