FLEX­I­BLE GE­NIUS

The magic of Du­cati’s trel­lis frame

Cycle World - - Components - By KEVIN CAMERON / Pho­tog­ra­phy by DREW RUIZ

WWhile talk­ing with former Du­cati en­gi­neer Cor­rado Cecchinelli at La­guna Seca Race­way one year, I asked him what spe­cial prop­erty had made his com­pany’s trel­lis steel-tube chas­sis so ef­fec­tive in rac­ing.

“It is be­cause it was de­signed by a ge­nius,” he replied sim­ply.

That ge­nius was Mas­simo Tam­burini, who was as­so­ci­ated with Du­cati through Ca­giva’s tem­po­rary own­er­ship of that com­pany. But ge­nius is a de­scrip­tion, not an ex­pla­na­tion.

When I ob­served to Colin Edwards that Du­cati Su­per­bikes vis­i­bly wal­lowed in turns, he said: “Yeah, they wal­low. But they dig in and go around the cor­ner.”

An en­gi­neer would call that wal­low by its proper name: weave. Weave is the side-to-side caster os­cil­la­tion of the rear of a mo­tor­cy­cle, at a typ­i­cal fre­quency of two to three cy­cles per sec­ond.

Edwards as rider had just been on point through Honda’s strug­gle to match Du­cati’s cor­ner grip with its RC51 Su­per­bike. Upon buy­ing and test­ing a Du­cati, Honda en­gi­neers dis­cov­ered it was half as stiff as the new Honda. A pro­gram of stiff­ness re­duc­tion was put in place. Each time side-to-side stiff­ness was re­duced a bit, Edwards said, “I could push a lit­tle harder be­fore it would start to chatter.”

Livio Lodi, di­rec­tor of Du­cati’s mu­seum and a bot­tom­less well of lore, tells the Tam­burini story dif­fer­ently. Ac­cord­ing to him, the Tam­burini fam­ily busi­ness was plumb­ing, so when a mo­tor­cy­cle be­long­ing to one of the fam­ily was wrecked, it was re­paired us­ing ma­te­ri­als and tech­niques at hand: pipe.

Du­cati’s trel­lis frame em­ploys steel tubes to join the steer­ing head to four widely sep­a­rated points on the com­pany’s 90-de­gree V-twin en­gine. Two are deep in the V be­tween the two cylin­ders, and the other pair is ei­ther high on the gear­box be­hind the rear cylin­der, or ex­tend­ing down­ward on both sides to grasp the swingarm pivot. Seen from ei­ther side, the trel­lis is strongly tri­an­gu­lated (as is a bridge) against lon­gi­tu­di­nal bend­ing. But seen from above, there is hardly any di­ag­o­nal brac­ing to pre­vent lat­eral—side-to-side—mo­tions of the steer­ing head.

There are two pos­si­ble rea­sons for omit­ting such di­ag­o­nal brac­ing. One is strictly prac­ti­cal: The en­gine’s in­take sys­tem oc­cu­pies

the lower part of this vol­ume, and an air­box of the largest pos­si­ble vol­ume must fill the up­per part, and nei­ther can be pierced by di­ag­o­nal braces. The other rea­son is to in­ten­tion­ally pro­vide lat­eral “give.”

Was the unique abil­ity of the trel­lis frame to hook up in cor­ners just an ac­ci­dent of ne­ces­sity? Or had Tam­burini found through his own ex­per­i­ments that the stiffer the front frame is made, the less feel, or warn­ing of grip loss, the chas­sis can pro­vide? If he did know, he was the only one in the com­pany who did. When in 2009

“Yeah, they wal­low. But they dig in and go around the cor­ner.”

Du­cati’s Mo­togp team re­placed the flexy trel­lis with the ex­treme stiff­ness of a car­bon-fiber front chas­sis, the re­sult was fre­quent loss of the front by 2007 cham­pion Casey Stoner. Filippo Preziosi, then-chief en­gi­neer of Du­cati rac­ing, would not know­ingly have planned such a disas­ter.

An­other fac­tor con­trib­uted to Tam­burini’s re­sult: On most Ja­panese four-strokes, it was tempt­ing to rigidly brace the steer­ing head to the cylin­der head di­rectly un­der it, but in the case of the Du­cati, the al­most-hor­i­zon­tal front cylin­der head was too low to be used that way. Thus, Ja­panese bikes tended to have stiffly mounted steer­ing heads, while Du­cati’s steer­ing heads were lat­er­ally flex­i­ble.

Honda, prov­ing to it­self the value of chas­sis lat­eral flex in the Rc51-ver­sus-du­cati Su­per­bike strug­gle, next ques­tioned the prac­tice of rigidly bolt­ing the for­ward part of their Mo­togp chas­sis to a cylin­der head. In­stead, they ex­tended their for­ward en­gine hang­ers down­ward to cylin­der or crank­case level. The re­sult was a lat­er­ally flex­i­ble steer­ing head like Du­cati’s.

Why was the Tam­burini trel­lis aban­doned in Mo­togp but con­tin­ued on most pro­duc­tion Ducatis? The likely ex­pla­na­tion is that ever-in­creas­ing slick tire grip in Mo­togp had fi­nally over­pow­ered the di­rec­tional sta­bil­ity of the steel-tube frame. As Casey Stoner put it at the time, “On that thing,” point­ing to the trel­lis-framed Mo­togp bike, “you can’t hit the same point two laps run­ning.”

All this tells us is that ac­ci­den­tally or in­ten­tion­ally, Mas­simo Tam­burini trig­gered the modern prac­tice of pro­vid­ing lat­eral chas­sis flex­i­bil­ity to give front-end feel and grip, but it was Honda that un­der­stood its value and sys­tem­atized the prac­tice.

From above, it’s ap­par­ent how lit­tle lat­eral brac­ing Du­cati’s trel­lis frames of­fered. Mas­simo Tam­burini’s de­sign proved that the stiffest frame isn’t al­ways the fastest.

A pipe dream: NCR’S ti­ta­nium trel­lis frames can be tuned to of­fer flex char­ac­ter­is­tics to suit the cus­tomer. De­scribe rid­ing style, skill level, and more, get a per­son­al­ized level of frame per­for­mance.

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