Cycle News - Archive Issues - 1990's

WORKBENCH GOLD CUP CLASSES 1. 50 ex: By Bri an Catterson s with many th in gs in life, th e sim pler a su bject appears on th e su rface, th e more co m p lex it actually is. So it is with suspen sion spri ngs. For the past two weeks we 've been discussing sp rings and sprin g rates, and it seems that th e deeper we get, th e mor e th ere is to discu ss. T h is week, we' ll ex plai n th e facto rs invo lved in deter,m in ing sp ring rates. . Accord ing to G il Vaillanco urt of Works Performance, th e formula for determining sp ring rat es is: Force at th e whee l x levera ge ratio t. To calcu la j~ th is, you need to kn ow three thin gs: The bike's purpose, the tot a l weig h t of th e bike with rider, and th e wheel travel. . For th e sak e of arg u ment, let's say that we've got a sma ll stree t bike with a total bike/rider weight of 500 lbs. and a single sho ck (for sim p licity's sake) mounted at th e rearward en d of the swingarm yieldi n g five inc hes of rea r whe el travel. Posit ioning th e shoc k in this manner makes for a I: I leverage 'ra tio , meanin g that o ne inch of shock absorber travel yields one inc h of actual wh eel travel. - In th is case, you' d want th e sus pe n sion to bottom with the force of th e tota l 500 lb . weight: 500 lbs. divided by five in ches of travel is 100 Ibs. per inch. .Since a spri ng is rat ed by th e force required to compress it one in ch, you 'd need to use a 100 lb. spring. A " . . . the formula for determining spring rates is: Force at the wheel x leverage ratio2. " 'J Now, if we were to retain our five inches of travel but positioned the shock's lower mounting point halfway up the swingarm, we'd effectively double the swingarm's leverage ratio to 2:1. So we'd need a 200 lb . spring to do th e sa me job, right? . Wrong. We'd need a 400 lb. spring. Sin ce we doubled the levera ge ratio , we'd now be using a shorter shock absorber with half as much travel to achieve th e sam e wheel travel. Thus that inch of wh eel travel now comes in a ha lf-inch of shock tra vel. So yo u' d need a 400 lb. sprin g. In th e case of dirt bikes, Vaillancourt says to use a factor of one-an da-half times th e total weight. Na tu ra ll y, things get twi ce a s comp licated wh en you 're talki ng dual shocks, and even more so in th e case of single shocks with linkages. But th e principles ar e th e sam e. Spea king of lin kages, the y're used ' to alter th e sp ring rate, wh ich makes th e suspension mov ement more or less progressive (rising rate or falling rate ), and to so me extent to allow motorcycle manufacturers to use a low er-quality shock, yet still obtain sat isfactory results. Work ben ch is a weekl y colu mn dealing with motorcycle mainten ance, performance and equipmen t. Have so m eth ing tha t Wo rkben ch ca n address? Drop a line to Workbench, Cycle News, P.O. Box 498, Long Beach, CA 90801·0498. 13 Plus25 . (Automatic Stock Only) 14 Plus30 . Springing to conclusions '3'·I-fi.,.• ==t.1.~ id l .@ G# !i*, ~ ~ ~ 6:30 AM 7:00AM 8:00AM 10:00 AM GATES OPEN REGISTRATION PRACTICE RACES 1990 2. 55 ex: 7-11 15. Plus35 16 Plus40 . 3. 85cc 7-11 4.85 cc 12·13 17. Women 5. 85 cc 14-15 18. Be ginner 6. 125 Youth 12-1 5 125cc & up 7.125 C 19 Quad B . 8.125 B 20. Quad A 21 . Open Novice 9. 125A 10. 250 C 11 . 250 B 100% PRO PURSEPAYBACK 12. 25OI5OO A GATE FEES $8.00 $4.00 ADULTIRIDERS CHILD (10 & under) ENTRY FEES AMATEUR CLASSES EXPERT CLASSES $12.00 $1 5.00 NO PRE-ENTRY_.ENTER AT THE TRACK! WORLD SPORTS AND AMA MEMBERSHIP REQUIRED (available at track). SCHEDULE DA TE LOCA TION DA TE LOCA TION G A T O R B A C K G Ai ORBACk :'. DADE CITY .DADE CITY MARION COUNTY (REDDICK) •. MARION COUNTY (REDDICK) COCOA .. .. . . . . ' COCOA « · .:·j ·· ··· ..:', '.' • · ·NoY.11 :..• . . .. · SEBRING . Oct . 7 S E B RING OVER $25,000 IN CONTINGENCIES AWARDED! TROPHIES AWARDED 10 PLACES BACK! TRACK DIRECTIONS: Galgrb ack' Exrt 1 at SR ·75 ·26In Gainesville. GoWest onSR -268 milesto NW 202, goNorth onNW 202 to CR-36. Gatorbackis onleft Hotel: Days Inn-I-75/S R-26Exrt #76. 904·332-303 3 Qualrty InnAlachua: 1 -751Hwy 44 Exrt#78. 1 904-462-2244 .QlllOlil: N. of Bee Une Expy inCocoa off USHwy 1. Look Dade City· Exrt 1 ·75at Hwy 50, Go east onHwy 50, follow Dade Crty Signs. Ho Da tel: ysInn- d #58. 813-973-0155 E MarigoCo unty (Red dick)' 8 miles No.of Ocala 20miles So. of Gainesville. TakeHwy441 to316. East 1/2mileon 316to first paved road on right. Hotel: Western Motel·904·732·6940 forsigns atCanaveral Groves. Hotel: Econolodge-305-632-4561 ~ Hwy 60East to lake Wales. South on27to Sebring. East onHwy 98. Hotel: Holiday Inn-813 -395-4500 P.O. Box 13246, St. Petersburg, FL, 33733 Call: (81 3) 822-8929 FOR FURTHER INFO CONTACT WORLD SPORTS FEVER RACERS WANTED • 20% Off Parts • Teet Support • Lowest Prices Right on. 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