Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/127291
eTECHNICAL ~ B uilding aFormula DTX racer By Brion eo ..erson he probl em with dirt track racing these days, it would seem , is that there isn 't an easy way to get started. Short of buyin g a quite pricey 500cc or 600cc Wood-Rotax, the neophyte dirt tracker has two avenues open to him - bu ild a bike himself, or scour T the Cycle N ews want ads for a su ita ble used mach ine, hopefully one wh ich was carefu lly assembled by th e previous owner (who obvious ly cho se the first route). T he other prob lem s are logistical be it new or used, you' ll be hardpressed to find a dirt trac ker close to you r home. If you're trul y lu cky, you' ll find one for sale out at the local race track (hopefully also loca ted nearby). If not, you 'll be faced wi th a lon g drive or, worse yet, ha ve to bu y a bi ke sig ht unseen and then deal with a truc king company and/or a frien dly local dealer to arrange for shipment. Ent er For mula DTX, the AMA's answ er 10 the problem of dwindli ng grass rool dirt track pa rticipa tion. Gettin g the green light When it was first suggested tha t Cycle News build a DTX bike, I immed ia tely du cked my head and cowered in fear. I had enough proj ects on my hands - th e last thing I needed was another. It turns out that I didn't really have a choice . It seems I' d once too often mouthed off to Editor J ack Man gu s th at I'd wa nted to try dirt tracking as a yo uth . but that ther e just weren 't any tracks loca ted near my form er home o n Lo ng Island, New Yor k, An d Mangus quickly remi nd ed me of that fact. Whether I like d it or not , I was go ing to be a dirt tracker.. The first th ing we needed was a bike, and a quick look in the han ga r-like expanses of the Cycle Ne ws test pool tu rn ed up a coup le of op tions. Honda CR500? Nah, too fast - it had already broken my wrist and twisted my knee. Kawasaki KX125? Nah , too small a nd too green . Suzuk i RM X250? Nah , it 's an enduro ... well, maybe ... The RMX has a few very desirabl e features for a dirt track machine - a comparatively heavy flywheel, smooth po wer characteristics, a rear disc brak e, even quickchange wheels. Hey, we were ont o somethi ng. J oe Columbero at U.S. Suzuki ga ve us the green light to permanent ly modi fy th e RMX , and we were on our way. O f course, there was lots of work to be do ne. Before we even got in to the serious dirt track modifications, th e bik e had to be made to look right. I mean , thi s th in g had a headlight and tailight , and di rt tra ck racers sim p ly do no t have lights . (Although in view of some of the di ml y lit sho rt trac ks we've seen, it mi gh t not be a bad idea !) The first of what would tu rn ou t to to be countless phone calls to the evereffervescent Robyn Figueroa at U.S. Suzuki resulted in our obtaining a front number plate and rear fender from a n RM250 motocrosser. Although th ese pans didn't simply bolt on , th ere was a minimum of trimming and drilling required to make them fit. Since we wou ld no longer need a fr ont brake, we' went ahead and trimmed th e brak e hose guard off the front number p late, .but we stopped sho rt of grinding th e brake caliper mount off the lower fork leg since we might one day like to try TT racing where a front brak e is necessary. While we were at it we removed the . front fender, th e speedometer/ odometer and its drive unit and cable, the fron t brak e rotor, ca li p er , hose , r eservoir and lever, en g i n e case guards, and probabl y some other useless (for flat tracking) stuff that we're forgetting, Sin ce we'd remo ved the speedo drive . un it, we needed some thing to take up the slack between the hub and the fork leg. Aga in we turn ed to the Suzuki part s bin , rep lacing th e drive u nit with . th e stock spacer from an RM. When we were through, the bike was at least sta rting to loo k like a racer. Next , we'd need to do something abou t the RMX's giraffe-like suspensio n. Wh ile long -trave l su spension wor ks great o n ro ugh tr ail s a n d mo tocross tracks, it's not the hot setup for dirt tracking. Tall, softly-spru ng suspension suc h as th at used by toda y's motocrossers does 'n ot mak e for good slidi ng charac teristics. Instead , longtra vel bikes lik e to compress th eir suspension, then suddenly rebound a n d hi gh -side the ride r into the stratosp here. Do-it-yourself dirt tracker