Op­ti­mum im­pact for Benz

Heavy hauler adds ma­jor fu­el­sav­ing gear — in the axles

Herald Sun - Motoring - - Working Wheels - JAMES STAN­FORD james.stan­ford@cars­guide.com.au

THE next gen­er­a­tion Ac­tros has been re­leased in Europe but Mercedes-Benz Aus­tralia is still car­ry­ing out changes to the old model.

Given the new truck isn’t due here for at least an­other two years, it makes sense for Mercedes to im­prove its cur­rent heavy hauler.

Mercedes will de­velop new ver­sions of the Ac­tros, de­liv­er­ing fuel sav­ings of 7-10 per cent over the ex­ist­ing model— a huge im­prove­ment. In one of the rare cases where the truck’s name ac­tu­ally makes a lot of sense, it calls th­ese mod­els Op­ti­mised.

The fuel sav­ings come down mostly to new hy­poid axles. Axle talk might make your eyes glaze over but they can make a huge dif­fer­ence in a big truck’s fuel ef­fi­ciency.

Hy­poid axles are not a new in­ven­tion but they are new for the Ac­tros. Most trucks run hub re­duc­tion axles, which means much of the torque mul­ti­pli­ca­tion hap­pens in the hub. In the case of a hy­poid axle, the ef­fect takes place in the dif­fer­en­tial hous­ing, in­board of the hub.

Hy­poid axles are 41kg lighter, in­creas­ing the truck’s pay­load slightly (by 82kg in this con­fig­u­ra­tion) and have su­pe­rior me­chan­i­cal ef­fi­ciency, mean­ing more of the en­ergy makes it all the way through to the wheels.

Mercedes says the change also af­fects the driv­ing dy­nam­ics be­cause of the more di­rect power de­liv­ery— it doesn’t need plan­e­tary gears.

To test the maker’s claim, Work­ing Wheels headed to the Lin­fox-owned test track at An­gle­sea, Vic­to­ria.

Mercedes had pre­pared two prime movers, an Ac­tros 2660 LS 6x4 with reg­u­lar hub re­duc­tion axles and the equiv­a­lent Op­ti­mised model.

We drove each truck with a sin­gle trailer, with a com­bined weight of 40 tonnes, and in a B-dou­ble with 58 tonnes.

There is a sense of deja vu when you jump be­tween the iden­ti­cal cabs— this is no bad thing as the Ac­tros has neat- look­ing cabin, with easy to op­er­ate con­trols all within reach. It doesn’t look any­where near as good or as mod­ern as the next gen­er­a­tion Ac­tros, a moot point for now.

The trucks use the sec­ond­gen­er­a­tion Pow­ershift, an au­to­mated trans­mis­sion with no clutch pedal.

The ex­ist­ing truck ran a 16-speed ver­sion of this trans­mis­sion, which is still used for the heavy haul­ing ver­sion that re­tains hub re­duc­tion axles. The Op­ti­mised Ac­tros mod­els use a 12-speeder.

Mercedes says that while it has fewer ra­tios gears, the trans­mis­sion is well suited to high­way haul­ing, adding that the po­tent V8 sit­ting be­low the driver means it can work well with less.

Our test truck is run­ning the 447kW (600hp) 15.8-litre V8. The Op­ti­mised Ac­tros runs the 11.9-litre V6 with 328kW (440hp) or 357kW (480hp) or V8s pro­duc­ing 380kW (510hp) or 410kW (550hp).

The reg­u­lar and Op­ti­mised Ac­tros get up to speed quickly around the oval test loop and feel very sim­i­lar. I get an in­di­ca­tion the Op­ti­mised mod­els feels slightly more nim­ble and seems to roll eas­ier but I could just be imag­in­ing it.

Our 30-minute back-to-back fuel test is too short to be de­fin­i­tive but it in­di­cates sav­ings of up to 10 per cent for the Op­ti­mised hy­poid axle mod­els.

Mercedes has had Op­ti­mised trucks in test fleets cov­er­ing hun­dreds of thou­sands of kilo­me­tres and show­ing sim­i­lar im­prove­ments. It says that in one op­er­a­tor fleet test held over 280,000km, an Op­ti­mised Ac­tros used $28,140 less fuel than sim­i­lar Amer­i­can trucks do­ing the same job over the same route.

Bet­ter be­lieve the hype: Fit­ted with lighter, more ef­fi­cient hy­poid axles, the Ac­tros makes fuel sav­ings of up to 10 per cent

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