Productivity drive08 June 2012

Construction trucks are offering more ways of getting their traction down efficiently these days. Ian Norwell reports from a Barcelona quarry on Renault Trucks' drive options

With the lion's share of heavy construction chassis sales in the UK going to the Swedes, it could be argued that the French are already beneficiaries, through Renault's family connections to Volvo. Same suit, different pockets. But this hasn't stopped Renault from fielding one of the widest ranges of construction chassis – and with some novel engineering.

For construction trucks, the compromise between traction on-site and fuel economy on the highway has never been easy. Double-drive chassis are unquestionably useful when the going gets tough, but all those extra drive shafts sapping energy on the road means wasted fuel.

Renault's solution is a part-time drive called OptiTrack, which provides temporary AWD without the heavy metal. A front axle is driven by a pair of hydraulic motors, supplied by an engine-driven pump. This allows continuous front-wheel drive with none of the transmission breaks that result from a gearbox arrangement. Naturally there is a deal of pipework, a hydraulic pump, oil tank and a cooling radiator, but that's still a 500kg saving when comparing a traditional 6x4 rigid tipper with a 6x2 fitted with OptiTrack.

Also, when switched off, the device uses no fuel so the payback comes with lower consumption and some extra productivity. However, there is a cost: at £15,000, it will take a while to repay the investment, even allowing for the initial lower cost of a 6x2. Nevertheless, Renault Trucks' UK commercial director Nigel Butler believes that as fuyel costs continue to rise, "the payback equation is shifting".

Certainly, a simple demo with a poorly loaded 4x2 tractor and tri-axle trailer is convincing. The combination's inability to get sufficient traction on a moderate quarry incline is immediately overcome with the OptiTrack button.

It's available on most rigid and tractor chassis, with the exception of a 6x2 tractor, but Butler suspects that changing legislation in France – moving 6x2 tractors to 45 tonnes – may stimulate an additional variant that could appeal in the UK. Maybe: but a traditional market that likes the staple 6x4 tipper is a hard one to budge, not least when it comes to resale. However, there are signs that operators with occasional traction and manoeuvrability issues are starting to consider alternatives.

Tridem gets a grip
Another traction option that has started to find favour in the UK is the 8x4 tridem. BOCM Pauls is operating four 8x4 Renault Lander tridems on animal feed deliveries out of its Preston site. The firm sees them as offering the best combination of payload, traction and manoeuvrability.

The arrangement sees a three-axle bogie layout at the rear, with two drive axles on twin tyres and a trailing single on the rearmost steering axle. The maximum bogie capacity allowed on the rear in the UK is 24 tonnes and, coupled with the largest front axle at nine tonnes, that gives a loading capacity of 33 tonnes, leaving one tonne of tolerance compared to a conventional 8x4.

Most apparent, though, is the improved turning circle over a regular 8x4 – so mixer operators working in tight urban locations come to mind. However, with the load capacity apportioned to the rear, the magic eight cubic metres might not be quite attainable. That said, two years ago, demand for the tridem was almost non-existent, but the search for every scrap of productivity is making operators look again at the options.

One that UK operators probably won't be taking, however, is Renault's Kerax Xtrem 8x8. Designed for applications elsewhere around the globe, where a weighbridge and any ministry men are often hundreds of miles away, it has a 50 tonne gvw and is expected to be routinely overloaded. A 32 tonne rear bogie and as much chassis flitching as can be squeezed in puts it firmly in the 'ready for abuse' camp. While not designed for UK customers, rumours suggest one mining operation in South Wales is happy.

Ian Norwell

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