Cycle News - Archive Issues - 1980's

dual-compoundtires , ' presid ent o f Moto T ech Intern a tio nal , who introd uced th e tires for Bridgestone. McAndrew p roduced a to uring lire whi ch had su rvived 10,100 street mil es o n a Yamaha Vent u re Roya le ridden by hi s Iather, a n d di spl a yin g w ha t h e ca l le d " u n typi ca l wea r p att ern s for a tou rin g ti re." (His father rid es so me 80 miles eac h way to work, incor-, porati n g th e len g th o f so u the rn Ca liforn ia 's Onega H ig h way, 30odd mil es o f so me o f Ca liforn ia's twi sti est tarm ac). T h is tir e clearl y ex hi bi ted th e differ en ce in co mpo u nds 'a nd th e resulting wear severely feath ered on th e edges, yet with pl enty o f virgin-l ooking tread rema in ing in the midd le. T he o n ly detriment (if it is one), is th e resu lting step from th e harder , and now hi gh er center tread down to th e softer a nd lower sh oulder ar ea . One wo u ld sus pec t that thi s would ca use th e tire to " fa ll into " 'corn ers m ore readi ly. Du al -compound tir es a re n ot a co mp letely new co nce p t, but in th e past, diff erent co m po u n ds were used on th e in sid e a nd o u tside o f th e tread - a softer co m p ou nd was used o n th e in sid e to promot e efficien t hea t transfer. Bridgestone is cu rren tly seeking a U.5 . p at ent on its new extrus io n procedure, whi ch co ns ists of sim u l- Spitfire SE17R sport tire rm ru m urn g roov ing to promote sta bi lity. A double-crowned radius profile is used , which th e mak er claim s pl aces more rubber o n th e gro u nd in th e co ntact a rea . Wh at this means is a slig h tly " trigo n ic." or tri angular, p rofile a t th e edges o f th e tir e to help m ak e th e transiti on to lean angles. a nd a flatter ce n ter ar ea to improve tra ction a nd promote hi gh mi leage. Asp ect ra tio (pe rcentage o f height to width ) acro ss th e ran ge is high a t 90% (tho ugh so me o f th e wider 5 17s a re 80%), which Brid gestone says a llows th e rid er so me warn ing wh en reachin g max imum adhes ion. (Lo wer aspect ratio tires tend not to be as predictab le.) Bridgestone decid ed to design tires spec ifica lly for front a n d rear usage, so eac h m odel is ava ila ble with a n " F" or " R " su ffix. T yp icall y, wh en a tir e is p rod uced. th e tread splice is co n figured so th at acce leration a t the rear whee l and deceleration a t th e front push th e sp lice tog ether , ra ther th an pull it apart. In using the sam e tire design front a n d rear, th e tir es must be reversed, o r mounted back wards, for use a t o p posite ends of th e machine. The manufacturer, th en , is forced to co m p ro m ise o n tr ead d esign for m aximum water di spersion. The 5 17 sport tire, whi ch succee ds th e 5EOI and 5 E02, features " Boo me ra ng" grooves a t fro n t an d a " Diamondback " pattern at rea r to p rom ot e efficie nt wat er rem oval , as well as stab ility a nd tracti on wh en cor- SHOULDER COMPOUND By Brian Catterson MONTEREY , CA, NOV. 18 Bridgestone unveiled a new range of Spi tfire touring, sport-touring and sport tires at a press co n ference and demons tration at Laguna Seca In ternational Raceway. These bias-ply tires introduce a new concept in tire manufacturing . II d d i d . ca e ua trea construc tio n (DTC). 14 Esse n tia lly, DTC co m b ines th e long mil ea ge of a hard-com pound tourin g tire with th e roa d adhesion of a softer-co m pou nd sp ort- rid ing tire, a ll in th e sa me tread ; th rough th e u se of d ifferin g ce nte r and sho u lde r co m pou n ds . T he center co m po und ' is harder for im p ro ved handling stability and wear resist: ~ nce wh ile .th e shou lde r c0!TI po u ~ d IS so fter for in creased cornenng gnp. The " du ro me try" or hardness of th e tire cha nges very littl e from one co m pou nd to th e o ther on a sin gle tir e, but th e re la tive resilien cy of th e two co m poun ds is different. (Brid- , gestone claims a differen ce of 3% in th eir 527 touring tir e, for exam p le.) The d ifference is im percep tab le to th e nak ed eye (a lth ough wiping th e tread with gasoline is sa id to show th e differen ce), so th e co nce p t was best illustrated by Tony McAndrew , Bridgestone's new line of Spitfire tires feature Dual Tread Construction. s concept which ut ilizes two rubber compounds in the same tire tread. ta n eo usl y ex trudin g two different rubber co m po u nds through one di e to produ ce one single .s h ee t o f fini sh ed tread material. T he new line of four-ply Spitfire tir es' is a vaila ble in three designations - 5 17 for sport bikes, 5 II for sport-to urin g , a n d 527 for h eav y tourin g. Ea ch has variabl e-depth . sho u ld er and ce nter ' groov es to provide uniform blo ck stiffne ss, a nd nering. The shoulder ar eas of th e 517 are made o f Bridgestone's sti ckiest, .lea st-resili ent co m p o u n d , whi ch ac h ie ves o pe ra ti n g temperatures . more readil y in n ormal street use. And although it is designated a sport tir e, Brigestone em p h asizes th at the 5 17 is n ot for racing use. The 527 touring tire was designed for high mi leage, and a n independent tire testing com p a ny, Long and

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