Cycle News - Archive Issues - 1970's

Gary Bailey's UMOa H ow to win They're Ours Removes MOTOCROSS * ap!sdn lI.10M l,uoM UNLESS .- 6 1/2 LIS. l!') nsp .... u ..0 Wei h Large 130cc Oil Capacity E II) ;> Part four: Setting up your motorcycle for racing, continued $119.50 Pre o Z INSTANT MA I L ORDER PAR TS: MAleo. PENTON . HUSKY. HONDA I da _ ar , Illua South Main St. Piqua, Oh io 45 356 15131 77 3-8034 Par ts a nd a ccessory or ders a dd SI.00 for handling. Ohi o resi dent s add 41 "/2 percent tax. Ban k Arn ertcaru , Master Cha rge, cash or mone y o rder o n ly. Perso nal checks must clear ban k p r i or t o S hipp i ng . Husky~ale 400 SC 450 OM 450 CR 250 WR $1195.00 $1195.00 $1 150.00 $ 1195.00 Large Stock Available '~ ~ ~\ON ~W ~ ~ Bike is just t o uc hing down afte r a lo ng, fast ju m p. Notice rear suspension is fully compressed. If you r bike does t his frequ en t ly a ro u nd the course and bottoms w ith a jo lt , your rear springs may be too weak . 7'ORC'(~\; 8730 Sepu lved a , Sepu lved a . CA (just no rth of Pa rthe n ia ) Spring preload "W e have th e parts " 1974 Montesa VR $1295.00 full price 213-785-4289 MXSALE GTMXB ~1X 175 A Mo"C 250 A MX 360 A S 454 959 1049 $1109 out the door SUNSHINE YAMAHA \V. 1010 Cha pman, Or ange, CA 714-633-0064 125·250·400 MOTO·X CHAMPION MACHINES ~~ ~. SALES·SERVICE·PARTS 10 Iron Horse Cycle 6009 Skyway , Parad ise . CA 959 69 916-877·2374 Spring rate is a m easurement o f how much force it ta kes to co m p ress th e sprin g. On a plain sp ring. if it takes 70 pounds t o co m p ress it o ne in ch then it wiII ta ke 140 pounds to co m p ress it tw o inches a nd so fo rth . Th e sp ring rat e do esn 't change be caus e th e sp ring is part iall y co m p ressed . In th e case a b ove , suppo se th e spring was sitting there co m p ressed iwo inch es. To get one more inc h of co m pression you wo uld ha ve to app ly a n addi tional 70 pounds of load on th e sp ri ng. The point is, u ntil the coils start touching each o ther or the spring closes up. it doesn' t kno w ho w m uch it has already been co m pressed and it co n t inues to wor k at its o wn spring ra te . wha tever th at is. People so me t imes ge L con fuse d b y th e ads o n shoc k abs orbe rs whi ch say th ey are "five·w ay" adjusta ble or so meth ing lik e that. The adjust men t refe rred to is on th e o u ts ide o f th e shock body a nd it is usually so me way to co m press the spring m ore o r less. The rin g th a t holds the bottom end o f th e spring has some notch es in it arra ng ed like sta ir s te ps. These notches fit o ver pins on th e shock body so when you rota t e t he r ing it moves up or d own on th e shock an d therefore co m presses th e spring mo re or less. This kind of co m p ressio n is not d ue to the ride r getting o n board a nd it is put into th e sp ri ng system be fore the spring act ua lly starts to wo rk as a suspension element of the motorcy cle. So th is kind of co m p re ssio n is ca lled spring pr eload. So me fr onL forks have a screwdriver adjustmen t a t the top whi ch turns a ca m on the ins ide of the fork tube. What the ca m d oe s is c ha nge the co m press io n of the fo rk sp rings while Rear Spring Chart Rider's Weight Over 200 po unds 185·200 155·185 130·155 Under 130 Rear Sprin9 Ra t ing 100 Ibs/ineh 90 Ibs. or 70190 dual ..at. 70 lb. or 60/90 dual -rate 55 lb. 45 lb. These are ball-park values that you can st art with to set up your rea r suspen sion. Bikes will vary i n weigh t by as much as 20 pounds or so, and t hat has an in f luen ce on rear spr ing rate s, ju st as the w eight of the r id er does . Also the bra nd of mororcvcle and the br and o f sh ocks w ill ma ke a difference. You h ave t o experimen t, but t he results are worth it. th e bike is just sitting there. an d this is an other form of preload. So wha t does preload do? It adjusts th e height of the moto rcycle with the rid er on bo ard and in some cases a passenger or some luggage. Preload is adj us ta ble for just that reaso n - rid ers don't all weigh the same and so me t im es they take on a passe nger or so me luggage, al though no t often on ra ce bikes . Let's suppose you have so me ni ce soft sp rings on the ba ck of a motorcycle - SO pounds per in ch. Because th er e a re two springs . it takes 100 pounds to co mpress th e rea r springs one in ch . Al so let 's sup po se th e t o ta l tr avel of th e rear sh ock is four inch es and th e mo torc ycle wei ghs exac tly 100 pounds at th e re ar. Now th e wei ght of the m otorcycle itself has co m p ressed the rear springs by one inch and that much travel is t aken o ut of the shoc k. Now you get on th e bike a nd yo u add another 100 pounds a t the rear end. The shock s co m p ress another in ch . You are not even riding yet and hal f of the sho ck travel is used up just to su ppo rt th e weight of bike and rider. It's better to have mos t of the shock travel availa ble for go ing o ver bumps so we will look for so m e wa y to uncompress th e shock. There is no wa y to un compress the sp ri ng its elf be cause it has to co m press that much to support th e weight. What you d o is gra b th e bo tt om of th e sp ri ng an d slide it upward s o n the body of the shock absorber . n tis lift s up th e back o f the m o t o rc ycle an d th e shaft pulls up o u t o f th e damper so th e damper now has m ore travel left for riding. If yo u look a t an y shock with an adjustable ring on the bottom of the spri ng yo u wiII see tha t is what the adjustment -is doing. OK, what do you make the adjustment for? You adjust p reload so when you are sitting on t he bike th e r ear suspcnsio n is j u s t barely co mp ressed . If sone other guy gets on and he is heavier th an you. h e will have to us e more pre load. You do t he sa m e thing at the front with spacers or with an adjustment if th ere is o ne . When you get o n the bike , th e front suspe nsio n sho uld j us t st art to co m p ress - m aybe a h alf inc h or an inc h . Wh en a su spen sion is bottoming out - whi ch means co m p res sin g co m p let ely du e to a bump - yo u ca n so rne rimes '

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