Cycle News - Archive Issues - 1970's

Part I .. Track testing at Willow Springs W~~~~~~~ ~~Wl~GJ~~~~~ By Bob Crossman The motorcycles The everpresent Kawasaki Z·I was chosen first for the ease of obtaining one (a phone call to Kawasaki Motors PR department snagged one for th e duration of the comparison) , and second for the availabilit y of aftermarket cast wheels. Preparation for the comparison included: slightly lower handlebars, Koni shocks for the rear, SAE 30 Torco fork oil for the forks , a new Subaki self-Iubing chain, and Lester cast wheels. As a back up bike, we brought along Mike Kilgore's Box Stock Production racer Kawasaki. Mike 's Z-I is set up almost exactly like the loaner from Kawasaki Motor Corporation . NOTE: We chose the Subaki Self-lubing chain and the Lester cast wheels for a combination of easy maintenance, and for consistency among all of the tires compared. Both Denny Berg and I agreed that the Lester wheels really made a major difference in how each set of tires felt. More road feel is transmitted through the cast wheels. This allow s the riders to get a better idea of th e plus and minuses of each of the 19 different tires compared. The tires Yokohama 's newest offering in the high performance field are the Roadflash 988 and 989 tires. Both tires carry a V speed rating. While .the 400VI8 rear tire is a patterned nre, the 325 VI9 front tire is novel in that it carries a rib design in the center and a pattern tread on the outside edges..On both the front and the rear ures, Yokohama has incorporated design features that are supposed to keep chain and /or motor oil off the tread face . Continental supplied us with what they refer to as the "Conti twins ." The K1I2 is a 510HI8 patterned type rear tire." The sales brochure that accompanied the tires indicated that the rear should be used with a 300D rim. The 325HI9 RB2 front tire is similar in design features to the « , The comparison - a rationale T his super tire comparison consists' of three separate test phases . The first phase is racetrack analysis ; the second is wet /dry skidpad testing and braking comparisons ; and the third is mileage potential and general!overall conclusions, Rather than a giant collection of super technical facts and figures, I opted for information that "everyman" can hopefully relate . to his particular brand of motorcycle and riding. I hav e tried to boil down the data collected into figures that will make the comparison easier to follow. In the first part of the comparison . Denny Berg (Co-owner o~ Rickey R,!c~r) and I took the Rickey Racer Van . two motorcycles , 19 tires and vanous test eqUIpment out to Willow Springs Raceway in Rosemond , California . For those of you not familiar with Willow, the track includes an almost constant radius uphill turn , a couple of up and down hill medium speed turns, and for good measure a couple of very fast and very bumpy corners. John McLaughlin calls Willow Springs the most abrasive roadrace track he has ever ridden on. We spent two days gathering and comparing data on the tire wear, hardness, and comparative lap times of the 19 different tires . It turned out to be a form of sensory overload. Intia l riders' impressions varied, but the back-to-hack lap times for both the riders and the tires really told a story. Learning to relate the way a tire felt out on the track to the way the rubber was flaking , smearing or peeling proved to be a slow process. Even harder to understand was the correlation between the way a tire felt and the kind of lap times the tire was consistently capable of turning. Some tires just felt fast , others really were fast. Other tires got so much traction that they put a tremendous strain on the motorcycle chassis, In some cases , the true potential of the tires could never be explored because of the chassis limits. Each pair (front and rear) of tires were measured for tread depth , pressure and hardness before the three lap break-in runs. Aft er the initial break-in period. the tires were run for five timed laps by each rider. Before and after each of the five-lap timed runs, the tires wer e again measured for tir e pressure, hardness , and tread ~r. Yokohama 988. The center of the tire is made up of four ribs , with the sides Of edges of the tire having two separate block patterns. Continental has gone to a great deal of trouble on the 510HI8 K1l2 rear tire to make sure that each of the individual tread blocks are braced against tread squirm. France was represented by the Mich elin M45 H & V rated tires. The 425VI8 rear tire has the stiffest carcass of all of the tires that we compared. That stiffness made the tire harder to install on the rim , but it also makes the tire more secure in the event of a sudden loss of air. The 350HI9 front tire has the same block tread design as ~ the rear , but the biggest difference between the two is the speed rating and the number of plies used in the construction of the tires. The A von Roadrunner tires that we used were a 470HI8, a 425HI8 and a 410HI9 , We opted ' to test two different rear tires from Avon because both are readily available in this country , and potentially the size difference would offer (or should offer ) some noticeable handling differences. The Avon Roadrunner tires arc s1m ila r in tread design to the ever -popular Dun lop K81, but arc more V·shaped than V-shaped. The Goody ear HP and GT tires are at first glance very similar. Closer inspection reveals that th e ML90 -19 front GT has both a rib and a patterned type of tread while the ML85 ·19 HP front has a slightly d ifferent aspect ratio and a pattern tread . The MR85·18 (4 75· 18) HP and MN90 ·18 (425 -18) GT vary both in the aspect ratio and the basi c size of the tires. Goodyear advertises the HPs as having a "Parabolic Tread Contour. " Both the GT and the HP series tires (rear) share a common pattern for the tread design . From Italy we tested the Pirelli Supersport MT18 . Both are V shaped and carry the same basic tread pattern on the 470H 18 and the 325H 19 size tires. The 470HI8 rear tire has been available on the American market for the past couple of years. The matching 325H 19 front tire has just recently found its way to American shores. The Dunlop K91 series tires are England's latest in the high performance field . Dunlop promotes the fact that these tires are direct descendants of the KR91 endurance racing tires. The 425VBI8 rear and the 41OV19 front tires are a prelly radical departure from Dunlop's accepted "t rigonic" design tires . Neither of these tires has the traditional V shape. Nor do these tires hav'e any major amount of shoulder where the tread ends and the sidewall begins. Last but far from least , we included the Dunlop K81 TTJOO in 425 /85H18 rear and 410H 19 front sizes. Dunlop refers to the K81 as a triangular low profile. 'The familiar V-sha pe and tread pattern have become a standard for production racers and racer-road types nationwide. Front t ire tread center wear Michelin M45 . . 5%, Dunlo p KS1 ~ 7% Yokoha m a S·% Goodyear GT - HP 10% Avon 18% Du nloo K91 22% , Pire lli M T1S 23% Contine ntal • 27%_ Dunlo p K91 5% Rear tire tread center wear Goodyear HP 7% Goodyea rGT 10% Avon 425 12% Avon 470 1S% Pi.elli M T18 19% Mich eli n M45 19% Continental 19% Yokohama 21% Dun lop KS1 25%_ 40

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