Cycle News - Archive Issues - 1970's

• I II -= ~ E ~ r--- 0') I""""'t ~ I""""'t l-< IlJ ..c t e now, .. etter I Sl.Clfl 0 ... u 0 The first gas shock in the M k II edition By Joh n Huetter A fter y ears of isolation from the mainstream . of motorsport technology , off-road motorcycle sus. penSIon has s udderily gone in just two racing seasons. Th e racing and rec reational rider have 14 go ne from a n y th in g- better-than-a-bed s p ri ng t o modified h ydr aul iC suspensions with longer stro ke an d travel to gas-damped suspensions in devo uri ng h ast e . The curve of technol o gical ch ange as it af fects o ur riding eq uip me n t and ha bits is still climbi ng. Next ye ar , totally new styles an d geo metries of suspen sio n are likely , Gas-fluid dam pers are no longer news. Improving their fun ction al o peration is. Notice t he use of t he adjective "funct ional " , Your rear units arc in tended to fulfill a function outside of th emselves; b asicall y to co m pe nsa te fo r all the forces acting on a wheel that is driving a bike forward an d bouncing all over the place at the same time. Some cle ver German has figured out that no t only do off-road dampers bounce straight up and down (as they ten d to do in n orm al street driving) but that they're de flected out of a st raig ht line track fro m many differe nt an gles , de pe nding on the attitude of the mo torcycle and the terr ain it is cu rrently traversi ng . There are also secondary forces that are working agai nst a smooth and co n tr o lled ' rid e like swingarm flex, re flected shocks from th e frame, etc. So, lifting the basic de sign from the Porsches, Mercedes, and Alfa Sports that ori ginally called for the dampers, then adding the experience of European rally and American o ff -r o a d which it o pera tes, b ut th at 's ano ther story .), and a pi ston rod guide th at seals th e flu id ch amber an d supports the pist o n rod itself. T hese Bilst eins would easily las t for two 4 5-m inute Gran d Prix mo t o s or more. A Two Days Trial rider logged 10,000 off-road mil es o n his . But they di d have tw o t ypes of failings and a third design omis sio n co m m o n to all motorcycle dampers. . . so far , First, with th e exact time depending entirely on riding co nd iti o ns, the O-ringe d floating seal eventually would wear enough to allow mixture of the n itrogen and fluid. When th is happened, co m pe tru o n, the friendly fo lks th at brough t you the fir st gas damp er in this co un try have come u p wi th a better one . The Bilstein Gasdru ckstossdam per is n ow ava ilab le in what , for co nven ience, we'll cal l th e Mk II form. (The Mk I and Mk II dis ti nc tion s are personal, not o fficial , designati ons. ) A lot o f us are n 't all t hat familiar with th e o riginal Bilstein adapted to mot o cr o s s a nd c ro s s -c oun tr y co m petiti o n, so before we ra mble o n abo ut the new goodies, re me m be r what we were all excited abou t 'wa y b ack about six months ago . Your basi c Bilstein (as th e say in g goe s) is o ne of th e purest ad aptations o f Dr. deCarbon's gas-fluid sep ar ation p at ent, o n which at least half of the current gas shocks are based. There is a sin gle tube (as opposed to the twin-tube con struction of most hydraulica lly-damped shocks) with a pressurized nitro gen cham ber separated from a chamber co mpletely filled wi th fluid. No gas or air bubbles exist or can get to the flu id - whi ch is wh y de Carbo n's basic idea works so we ll. No ca vitation of t he flui d. In s i d e the Bil s t ei n tha t us technological re tar ds in the dirt riding. business got familiar with la st year is a floating O-ri ng seal that sep arates the nitrogen and fluid, a more or less c o n v e n t i o na l damping piston incorporating the orifices that ac tually co n tro l bump and rebound damping (The design of this piece benefits fro m the co nstancy of the medium through The better Bilstein fitted as recommended. Heim joint down. he avy end up. The better the basic geom etry of the motorcycle. the better th e shock responds. a: w ~ w :l :I: Z :I: o , ., >-

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