Cycle News - Archive Issues - 1980's

Bias-belted t ire Radial tire Carcass : 65 ° -75° 4: Belt: 18°-22° 4: Carcass : 85° -90° 4: Belt: 0 ° -22° 4: l-< Cl.i ..0 o ... u Where a bias-ply t ire angles the ca rcass cords for sidewall strength. a radial t ire's cords run directly from bead -to-bead, o holds th e 600cc and 750cc Stock Production lap records at Willow Springs and who has won 20 of 23 AFM road races h e's entered thi s year. With th e same FZ750 in stock co nd ition , T o land set the 750 Stock Production class record at II :34.49; during th e 24-h our, with a ra cing slick on th e front wheel, Toland went 1:32.00 o n th e FZ. With Hi -Sports m ounted front (\20/80- 16) a n d rear ( 160/80- 18). T ol and went o u t a lo ne o n th e track a nd turned I:33s o n hi s seventh through 13th laps, the fastest being 1:33.45. The FZ750 was th en fi ued with a new 120/ 80-16 Dunlop 39 1RS front tir e (based on th e 39 1R but with new co mpou n di n g a nd a modified tread design ) a n d a 130/ 80- 18 Dun lop K700R radial rear tir e. The ins ta lled ci rcu m ference o f th e Dunlop wa s 82.25 inc hes. larger th an th e Mich elin 's 81.5 in ch es. Dunlop spokesmen were ca refu l to poi nt o u t th at th e rad ia l felt co mp lerely di fferent th an a bias-belted tire, a nd quot ed race r Kevin Sch wa n tz (w ho rod e o n Dunlop radials for a recent Motorcycl ist maga zin e tire test) as sayi ng tha t. enteri ng a corner, th e rad ial feel s like it will sli de o u t. but if th e rider co nt in ues to push . it doesn 't. With those ca u tiona ry word s. T ol and went ou t o n th e track. starting out slo w ly , working down th rough 1:37s and 1:36s into 1:35s a nd . fin ally, 1:34s: hi s last fo ur of 13 laps were I:34s. th e best being 1:34.31. T oland ca m e in and reported th at th e gea rin g wa s off probably one tooth , that engine speed exi ting co rners was a co u p le of h undred rpm lo wer than w ith th e Michelins. Toland figured that cha nging gearing would be worth a t lea st a co u p le of tenths o f a second in lap times. He also reported that. if n ot for having heard Sch wa nt z's exp la na tio n of how radial s feel , he would have com e in aft er a few laps. The rear tire stepped out entering a corner . T o la nd said. but didn 't continue to slide. a nd once he made h imself deal with the unsettling feeling. he didn 't hav e to back off th e throttle. Wh en th e tire d id slide. it ca me back in smooth ly: aga in, he d idn 't have to ge t o u t o f th e th rottle. H aving said th at . T ol and went o ut for a nothe r sess io n. thi s time with a flock of journalists o u t on the track ridin g th e Californi a Superbike Sch ool's fleet of GPz550 Kawa sakis, all fiued with various Dunlop p rodu ct s. Toland wa s into 1:35s and 1:34s in stantl y. working traffic every other lap. hitting a I:33.92 on hi s sixth o f 13 laps. a 1:33.94 on hi s eig h th an d a I :33.93 on hi s I Oth; hi s other fin al laps were I:34s. It felt like he wa s going arou nd turn two a t Willow Sp ri ngs sligh tly side ways a t th at p ace. Tola nd report ed , but h e co u ld stay o n th e gas as th e bike went around th e co rner. H e left bla ck strea ks slid in g arou nd turn thre a co u p le o f tim es wh en he really e pushed ha rd into th e corner . but th e bike didn 't go into a big side wa ys slide o r cross up. The most difficult cha rac teristic to ge t u sed to with th e radial was the way it felt going into th e co rners: it wa s a case o f having to o verri de tro ubl e-alert se nses and gra b th e th rottle rega rdl ess. On th e o ther hand . th e radia l deli vered a smoothe r ride over th e ripp les enteri ng turn nine - a pl ace whe re th e FZ on Hi -Sports o ften feel s like it's ski tte ring both wheels slig h tly and didn 't cha tte r a t a ll. The K700 radialis closer in performance 10 th e Hi -Sport than a re th e Dunlop K391 R a nd the new K39 1RS bi a s-belted tires. Wi th ou t mak in g gearing cha nges to allow for th e K700's lar ger insta lled circu m ference. T oland o n th e Dunlop-equipped FZ750 was able to co me w ith in half a seco nd of h is best time o f th e da y on th e sa me bike fitt ed with H i-Sports. It 's reasona ble to bel ieve th at. wit h one m ore tooth o n th e rear sprock et. Tola nd and the Dun lops cou ld have co me with in a few ten ths of seco nd of Tola nd and th e l\Iich el in s. Wi th more tra ck t ime to ge t used to dea ling with th e stra nge transiti onal feel o f th e Dun lop ra dia l, it 's p robable th at T oland co u ld ha ve gone as fast on th e Dunlop radial as he d id o n th e HiSport. In strict performance terms. measured by lap times on a ra ce track . th e Dunlop K700 rad ia l ma y have given Dun lop parity with th e Hi -S port. But the K700's unique feel ca n not be overloo ked. To go fast on a K700. a rider must ignore feedback th at wo u ld. o n a bias-pl y tire. be warn in g o f impending trouble. That mak es it harder to go fast o n a K700 th an o n a H i-Sport, and th e K700 is a lso m ore expe nsive tha n a Hi-Sport. It may be th at a radial K700 used on th e street o ffers a better rid e and superior m ileage. although th at ca n 't be determined at a race track. T he K700' s wear after a bo u t 30 laps o f Willow Sprin gs looked to be g rea ter th an th e typ ical wear seen on a H iSport after 30 laps at equivalent speeds. It a lso may be th at future versions o f th e Dunlop K700 will blow a way the Hi -Sports an d allow sign ifica nt ly faster lap tim es. a ll other th in gs being equal. But here a nd now. for race tra ck use. th e radial Dunlop K700 offers no perfo rmance adva n tage over rhe Michelin H i-Sport. feels weird to ride o n. a nd cos ts sign ifica n tly more. Bu ilding ultra -low -profile radi al s for existing stree t motorcycles desig ned to use tires with h igher sidewalls doesn 't make sense: the stock rims would be too narrow for the tires. a nd th e sma ller tire ci rcumference would greatly red uce cornering clearance a nd a Iter geari ng as well. Dunlop has done so methi ng else. Beneath the tread: Dunlop 's K700 Sport Radial has two rad ia l carcass plies, with three belts running the circumference of the ti re. add ing a strip of hard rubber reinforcing in th e sidewa ll o f the K7oo. T h e tr ick . say Dunlop eng in eers. was to get th e compound in g ofthe ru bber in th e strip j us t righ t: th e ru bber had 10 be stiff. yet resilient. flexibl e. yet n OI too flexibl e. The seco nd ca tch is th at radia l tir es are more d iffi cult a n d expe nsive to build. a nd th ere's so me quest ion as to wh eth er or not th e ben efits gai ned with a radial motorcycle tire are wo rt h th e ext ra cost . Wh ich brings us to Dunl op's K700, and why th e ti re was made a t a ll. In a word . th e K700 exists beca use o f th e Mich elin Hi-S port. a biasbelted. DOT-approved street-lega l tire based on th e bias-belt ed Mich elin SFII a nd SG22 raci ng slic ks. built with nylon carcass plies and Kevlar belts. (Miche lin Hi -Sport rear tires a re availa ble in 160/80- 16. 160/60- 17, 130170-18 , 140/70- 18 a nd 160/60-18 sizes with retail prices ranging from S I 17 to $ 137 depend in g upon size). High -performance tires targeted a t produ ction racin g - which requ ires' street-legal tir es - in th e pa st were based o n stree t tires with co mpou nd in g an d m aybe co ns truction chan ges. Dunlo p. Metzeler , a nd Co ntine ntal h ig h- perfor m a nce tires a ll hav e th a t approach in co m m o n. Michelin took a racin g lire a nd mad e cha nges to make it stree t legal : th e co m pany built min im al tread g rooves into th e TFll a n d TG22 tires, u sed th e sa me co m pou n ds as in th e SFII a nd SG22 rac ing tir es. got DOT ap p ro va l. an d sta rte d mark eting th e tires for p roduct ion road racing abou t a year ago , Before Mich el in introduced th e H iSport. Du nl o p 's bias- belted 39 1R Sport Eli te do m in a ted prod uctio n raci ng a nd seized th e lion 's share of t h e high-perfo rmance street t ir e marke t n a tion wi de. with Merze ler doing well in so me regions. BUI the H i-Sport s hooked u p better. a llow a far better drive o u t of corners, a nd have ge nerally-superior tracti on co m pa red to Dunlops a nd Metzeler s, a t th e cos t of some reducti on in co rnering cleara nce ca used by a relativel ylow profi le. Show up a t a race track n ow. a nd Michelin is lik el y to ha ve more tires o n m ore mach in es. a nd more win s a t the en d o f th e day. Fa cti ons inside Dunlo p advocated tr a ns for mi ng Dunlo p 's KI 33 a n d K149 bias-belted (nylon carcass/ Kevlar belts ) racing slicks int o DOT a p proved raci ng tires. BUI. the way insi ders tell it now . th e com pany felt th at tir es like th e Hi-Sport represented th e peak o f bia s-ply development , that th e bia s-pl y tire a s a type wa s at its limit. having reach ed th e end of development on co m pou nd an d tread: mat ch in g th e H i-S port w ith a nother bias-ply tire would on ly be a short-term so lution. Inst ead. th e co m pany looked to G rand Prix road raci ng. where ra dia ls h ave tak en hold in th e 500cc class in response to ra pi d in-race hea t bu ild up a nd loss of tracti on su f£ered by the best bia s-pl y racing slicks . " Ra dia ls .p u t 500 GP racing back on th e m ap ," three-time 500cc World Champion Kenny Roberts tol d the press. "T he radi al is more p red icta ble than th e bia s-pl y tire. Before th e radi al tires. th e 500s weren ' t much fun to rid e. Before. the bia s tires would last a bo u t IO laps. With th e radi al s. you GIn rid e it as h ard o n th e last lap as o n th e first. T he re's a better co nt ac t p at ch . T here 's better traction. In Gra nd Prix raci ng, rad ial s have opened u p a who le new door. If yo u 're gon na go raci ng. you 've got to ha ve a ra dial tir e." • 7

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