Cycle News - Archive Issues - 1980's

~ Radials that work and some that don't . e··· '" J: s w II: :) o o ~ - --1 >- '" o ... o J: 11. Bridgestone's new 1 10/80-18 Cyrox-03 front (left) and 140/70-18 Cyrox-04 radials are standard eq uipment on 1986 GSXR750s im po rt e d into the U.S. By John Ulrich There are a lot of theoretical advantages to radial motorcycle tires, including damping chassis forces before they start a wobble, a sm oo ther ride over bumps, less cha tter, a lack of tire growth a t high speed . in creased load-carry ing ability, cooler running, lo nger mi leage. But the last tim e we tested streetlegal , high -performance radial rno to rcycl e tires a ga i nst the best street- 24 lega l, high-performan ce bias-belted motor cycle tires, th e radia ls were less th an impressive. In that co m p ariso n at Willow Springs In terna tional Raceway lasI O ctober, usi ng a Yama ha FZ750. the Dunlop K700 ra dials offered a bo u t th e sam e traction as Michelin H iSports, bUImade the motorcyc le m ore di ffi cull 10 ri de fas t: the tires had a n uncert ain feeling going into turns, feel ing lik e the y were go ing 10 slide aw a y. T h e feeli ng, if it ha d been experienced on a bias-belled lire. wo ul d mean im pend in g trouble, a nd th e rid er had 10 overcome th e n atu ra l a nd usual reacti on of backing off t he th rottle in order 10 rid e fast. T he radial s were smoother over bu m ps bu t the Hi-Sports fell m ore secure a nd ga ve the rid er more co nfidence, wore less quickl y a nd in ge n era l wo rked better. At th e lim e, it seemed lik e th e radial . which Dunlo p told thepress was th e lire 10 kn ock o ff Mich elin 's dom ina nce in p roductio n -class roa d racing, was a d ifferent, bu t dec ided ly no t superior . approach . To i o p it o ff', lh e rad ia ls COSI mu ch more. Whic h brings us 10 a no ther p lace, an o th er li m e. a nothe r set o f ci rcu mstances. inv olv in g different moto rcycles. The occas ion wa s the th e worldwid e press la u nch of th e 1986 Suzuki GSX R750 a nd GSX R 1100 a t Laguna Seca Raceway, a nd the bikes were filled with ra dia ls. This rirne.jwo co mp anies provid ed th e radial s, which Suzuki engineers were most in terested in due 10 the ir tend en cy 10 prevent wobbles wh en acce lera ti ng hard o ut o f bumpy comers. The GSX R750s were filled wirA Br id g es tone 110/ 80- 18 C yr 6 fc: : 03' (fro m) and 140/70-18 C}Tox-04 (rea r) radials. Suzuki GSX R750s co me with relativel y wide wheels, a 2.50-18 from a nd a 3.50-18 rear; compare tha t 10 th e FZ750's 2.75-16 from wh eel an d 3.00-18 rea r wh eel. O n the firs t of two da ys of rid ing, lh eGSXR l lOOs were filled with Dun lop 110/80- 18 K701 (front) and 150/ 70-18 K700 (rea r) ra dia ls. On th e seco nd day, the GSX Rl lOOs wo re Brid gestone I 10/ 80- 18 Cyrox-03 (fro m) an d 150-70-18 Cyrox-04 (rear ) rad ia ls. GS XRI 100s have even wider wheels th a n GSX R750s. a 2.75-18 Iro n t a nd a 4.00x18 rea r. T he biggest news from the first day of riding a t Laguna Sera was that th e GS XR750s filled wit h the Bridgeslone ra dials displayed no n e of the stra nge feel we experi enced with the FZ750 and Du n lop radi als at Will o w Springs. T he bikes fell norma l goi ng into turns and didn 't wobble like the 1985 GSX R7505filled with bias-belled tires ridde n by th e pr ess in j apan a year ago. The Bridgeston es o ffered reasonable trac tio n but tended 10 slide durin g accel era tio n o ff co rne rs, especia lly o ff slipper y rum nine a t Lagun a Seca. Compa red 10 th e Dunlops we tri ed o n th e FZ750 at Willo w, the Bridgestones were a revela tion . Bridgestone engi neers o n th e scene told members o f th e p ress that th eir radial lire wo rked bett er th an Dun lop's because Bridgestone used KevJar in serts 10 stiffen th e sidewa lls , vs. Dunlop's hard rubber inserts, BUI th a t theory h ad 10 be a ba ndon ed a s soo n as th e Ame rican journali sts a t the la u nch cl im bed o n to GSXR llOOs wi th Dunlop radials; th e Du n lops on th e GSXRI 100s felt as normal as th e Bridgestones o n rhe GSX R750s. a nd slid far less off co rne rs despite the GSX RIIOO's vas t horsepow er advan tag e and heavi er weight . On th e GS XRlIOOs. the Dunlop radial s displa yed no obvio us fau lts and appeared 10 be race worth y, The GSX R 1106 I wilh . Dunl op ' 'rad ia ls ha ndled better th an the GS XR 750s wi th Bridgestone ra dia ls. Looking at the tires after severa l la ps, th e Dunlo ps looked li ke they were worki ng well a nd were sui ta ble for ri di ng o n the race track, T he Bridgestones ha d th e g reasy look of a lire not working right on a given track, the look that sends a racer looking for a d ifferent compound. The biggest demonstration of the difference in performance bel ween the Du n lop and Bridgestone radials ca me on the second da y, wh en the GS XR 1I00s were filled with Bridgestones. Two Am eri can journa lists rep resen ti ng monthl y magazin es cras h - ed and severa l carn e in wit h sto ries of fu ll-loc k slides over the left-h and crest just af ter the SIan/ fin ish lin e. The combina tion of th e h igh-horsepower GS X R I IOOs a n d th e Bridgestone radial s was not a good one. The bottom line is that Dunlop ra dial s wo rk o n motorcycles with sui ta ble rims; bi kes with wide rim s allow radia ls 10 be used withou t a ny handling quirks confounding or u nset tling the rider. The Du nl op radia ls found on the GS XR I I00 are far superior 10 the OEM tires found on any other big japanese street bike. judging by what we lea rn ed rid ing on th e race tra ck in japan , at Willow Th is d iag ram of a Du n lop radial shows the hard- rubber ins e rt (c a lle d the apex) used to stiffen t h e s idewall of the t ire . Th e c o m po u n d of the apex g reatly affects t h e fee l of the t ire as the motorcycle enters a turn . Crown .,....--- Cap Plies ~----Belts Carcass Apex .. __- - Bead I

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