Slip & Slop

PowerTorque - by Allan Whiting

PowerTorque
Issue 44

One of the classic situations on many Aussie construction sites is the bogged small tipper or tradie's ute. The vehicle gets in there okay, but then can't get out, and many's the vehicle that's been damaged by over-zealous attempts to extract it. Enter the Isuzu NLS 200, which is an all-wheel drive version of the NLR range and comes as a cab/chassis, crew-cab/chassis and a short-cab tipper.

Because Isuzu already has a high-ground-clearance, low-range-geared truck range with its NPS models there's been no attempt to make the NLS a go-anywhere machine. Rather, it's an NLR with additional traction capabilities, for when the terrain becomes loose or slippery.

This derivative of the NLR family employs Isuzu's narrow cab, atop a three-litre, four-cylinder engine and five-speed manual box, driving to a dual-tyred rear axle, but there the similarities end. The NLS has a unique front suspension that's independently sprung, like the NLR's, but with forged upper and lower arms. The springs are torsion bars that run aft to the lower control arms from front cross member anchors. This suspension design provides plenty of free space for front drive half-shafts to connect to freewheeling hubs.

Drive to the front chassis-mounted differential comes from a single-speed transfer case with viscous coupling unit. Front axle drive in the NLS is activated by a simple push button dashboard switch and verified by a light in the instrument panel. (The more off-road-oriented NPS model has two-speed transfer case and mechanical front axle engagement.)

At the rear end, the NLR's drive axle is retained, but it's slung under the leaf spring pack to improve the truck's belly clearance. Also retained is a transmission parking brake.

With 110 kW and 375 Nm pushing it along, the fully loaded NLS 200 Tipper had a handy turn of speed and easily kept up with Melbourne's traffic. Peak torque, on paper, isn't all that flash, but there's ample lift-off grunt from idle, making progressive speed build-up effortless. The synchro' box combined with a light clutch that had good friction-point feel to make town driving a breeze.

Isuzu sought very flexible constant velocity joints for the front drive-steer arrangement, giving an excellent 35-degree wheel cut angle on the inside wheel at full lock, so manoeuvrability wasn't compromised.

Handling on smooth surfaces was flat and predictable, and ride quality on broken-up secondary bitumen was excellent. ABS-controlled, disc/drum braking was powerful and stable on slick surfaces. At this point in our evaluation, the NLS 200 Tipper felt the same as a 4x2 model.

We ventured onto wet, corrugated dirt, en-route to our off-road test course at Rob Emmins' Melbourne 4WD Proving Ground, and, as expected, the truck moved around through the effects of bump steer and tyre-grip reduction. Time to check out the 4x4 system.

Isuzu has fitted free-wheeling hubs to the front axle, so that the front differential can be isolated when not required. We locked the front hubs and, once under way again, pressed the dashboard 4x4 control button. Directional stability was immediately improved and the steering had much more feel. There was no noticeable noise increase and no vibration.

Although this is a part-time 4x4 system, there's a viscous coupling in the front axle transfer case, so the NLS 200 can be driven with 4x4 engaged on all surfaces and at all speeds. Drive an NPS like that and you'll experience 'wind-up' in the driveline and also risk transmission and axle damage. The only penalty from full-time 4x4 operation, in the case of the NLS, is a slight increase in fuel consumption.

At the Proving Ground there was typical construction site mud that made access by 4x2 vehicles quite impossible - an ideal test situation for the NLS 200 Tipper. We appreciated four-wheel-drive traction on the slippery downhill slope to the site area, as the truck adopted a slight sideways attitude. Thankfully, the exhaust brake combined with 25:1 gear reduction in first cog to control our descent without the need to touch the wheel brakes. In similar circumstances, a 4x2 NLR would have been extremely difficult to control, because exhaust brake engagement may well have locked up the rear wheels, and touching the wheel brakes could have locked up the steer axle.

We ventured onto the muddy flats with some trepidation, knowing how slippery this black soil venue can get, but we were surprised at the ease with which the NLS ploughed through this goo. The mud was thick enough to clog the gaps in the rear duals, squeezing out the hand-holes in the wheels like sausage mince! We made a series of tight turns, trying to catch out the 4x4 system, but the viscous coupling kept torque flowing without any trace of binding. Impressive!

The only downside we could discern was the woeful seating the NLS shares with its NLR cousins: shapeless, thin chairs that have progressed only a short way from the average park bench. You could live with them for metro stop-start work, but not for any rough-road or long-distance driving.

Given that you could slot in a pair of decent individual seats in place of the three-occupant compromise seating that comes standard, the NLS 200 looks like a vehicle that should have appeal to plenty of Aussie operators. Priced right, it could extend Isuzu's market dominance even further, but therein lies the 'rub'. The NLS 200 cab/chassis has a RRP of over 63 grand, which is almost $14,000 more than the 4x2 model. Our guess is that they'd move much more quickly out the dealership doors with an ask of around $55,000 - the price of a top-shelf crew-cab 4x4 ute these days.

Our conclusion is that the NLS 200 is an excellent 'traction truck' offering significant benefits to those who venture off the black top and onto gravel roads and rough sites. It's not intended to have the off-road ability of the 83-grand NPS, but has much more tractive grip than any 4x2 vehicle.