4 x 4 Australia - - Contents - FRASER STRONACH

IT IS a read-it-and-weep story if you’re a Holden fan, and it’s called the Chevro­let Col­orado ZR2. It’s a brand new off-road-mod­i­fied Col­orado ute made in the USA, but only for North Amer­i­can mar­kets. Ef­fec­tively it’s show­room and off-road cus­tom all in one.

The core ve­hi­cle is our Col­orado, diesel and all – a new en­gine to the US mar­ket – but it also comes with a petrol V6 teamed to a new eight-speed au­to­matic.

ZR2’S off-road en­hance­ment starts with a 50mm lift, 90mm wider front and rear track, cham­fered front and rear bumpers for bet­ter ap­proach and de­par­ture an­gles, skid plates for the en­gine, gear­box and trans­fer case, tubu­lar rails to pro­tect the rocker pan­els, heavy-duty front sus­pen­sion con­trol arms, and 31-inch ATS on 17s.

But that’s only the start of things. It also gets driver-switch­able front and rear lock­ers, where our Col­orado doesn’t even get a rear locker let alone twin lock­ers.

The ZR2 also gets Dy­namic Sus­pen­sion Spool Valve (DSSV) damper tech­nol­ogy, which only a few years ago was the stuff of For­mula One, specif­i­cally the Red Bull F1 cars that won the driver’s and con­struc­tors’ cham­pi­onships from 2010 to 2013. DSSV is also seen up and down the pit lane at the Le Mans 24 Hour and has been used in high-end sports cars such as the As­ton Martin One-77, the Ford GT and GM’S own Ca­maro Z/28.

The DSSV tech­nol­ogy comes from

Mul­ti­matic, a Cana­dian en­gi­neer­ing com­pany that sup­plies the au­to­mo­tive in­dus­try with spe­cialised parts and ser­vices. DSSV is no­table for many rea­sons, not least for be­ing rel­a­tively sim­ple and very cost ef­fec­tive given the high level of so­phis­ti­ca­tion. The fact that F1 tech­nol­ogy of just a few years back can be made af­ford­able for a pro­duc­tion car tells the story.

The DSSV’S so-called ‘spool’ valves are small metal cylin­ders, roughly half the height of the com­mon C-size bat­tery, that re­place the flex­i­ble shims used in conventional dampers to con­trol the damp­ing force. The cylin­dri­cal spool valves have var­i­ous ports that con­trol the flow of the hy­draulic fluid and there­fore the damp­ing force. More im­por­tantly, the shape and the size of these ports can be var­ied al­most in­fin­itely to pro­duce the re­quired damp­ing force.

The ma­chin­ing of these ports is done us­ing fine-con­trol robotics. Mul­ti­matic has spe­cial soft­ware that al­lows the damp­ing char­ac­ter­is­tics to be de­fined by nu­mer­i­cal val­ues, which are then used to de­ter­mine the sub­se­quent port ma­chin­ing in the spool valve.

The client com­pany, in this case GM, spec­i­fies the sep­a­rate re­bound and com­pres­sion damp­ing curves it wants as a start­ing point for sus­pen­sion tun­ing, and Mul­ti­matic feeds that data into its soft­ware. In the case of the ZR2, Mul­ti­matic ap­par­ently then ran 15,000 sim­u­la­tions be­fore a sin­gle part was ma­chined, thereby re­duc­ing the re­al­world tun­ing and de­vel­op­ment time to a quar­ter of that nor­mally re­quired for a man­u­fac­turer to sign off on a sus­pen­sion tune.

An added ben­e­fit of us­ing these ma­chined spool valves com­pared to flex­i­ble shims is that they are eas­ily pro­duced and have vir­tu­ally no vari­a­tion from part to part, which is a prob­lem with conventional dampers where damp­ing force can vary by up to 10 per cent be­tween two sup­pos­edly iden­ti­cal dampers at mass-pro­duc­tion tol­er­ances. Typ­i­cal DSSV dampers use one spool valve for com­pres­sion damp­ing and a sep­a­rate spool valve for re­bound damp­ing.

The ZR2’S sys­tem builds on this by em­ploy­ing two dif­fer­ent com­pres­sion-damp­ing spool valves, one for nor­mal road use and a sec­ond that au­to­mat­i­cally comes into play for high im­pacts on the front end when land­ing off some­thing like a jump or hit­ting a deep washout at speed. That means the sus­pen­sion can be fine-tuned for both road driv­ing and hard off-road driv­ing with­out one com­pro­mis­ing the other.

In­ter­est­ingly, GM didn’t wish to use its elec­tron­i­cally con­trolled ‘Magneride’ vari­able damp­ing sys­tem (see side­bar) on the ZR2 as it is re­port­edly more heat sen­si­tive and more com­plex than DSSV, which has no elec­tron­ics and is less im­pacted by tem­per­a­ture and damper fluid vis­cos­ity.

Will all this come to a Col­orado near you any­time soon? Prob­a­bly not, un­for­tu­nately. The ZR2 is pro­duced in left-hand drive for the US and Cana­dian mar­kets. Our right-hand drive Col­orado is built in Thai­land. Not that they couldn’t build a ZR2 in Thai­land given most of the parts are add-ons with only the lock­ers re­quir­ing re-en­gi­neer­ing work. Bet­ter go com­plain to your lo­cal Holden dealer.

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