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ROADTEST

21st February 1991
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Page 42, 21st February 1991 — ROADTEST
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Which of the following most accurately describes the problem?

IV-B 1720

Iveco Ford Cargo 1721. That loading tolerance is due to a beefed up front axle. Now plated at 7,100kg, against 6,700kg for the 1617, this allows 600kg of load distribution tolerance against 200kg for the 1617, which should help in multi-drop, diminishing-load use.

The 1720 derives its extra power from charge-cooling the 5.95-litre turbocharged 0M366 engine that was carried over from the 1617.

The result is 155kW (21Ihp) at 2,600rpm and 646Nm (4761bft) of torque developed between 1,400 and 1,500rpm, measured to EEC 88/195. These figures represent 20% more power and 13% more torque than in the 1717.

Among our selected rivals this puts the 1720 at the top of the class for power. With one of the smallest engines, it is no surprise that it loses out to the 8.27-litre Cummins 6CT-powered Cargo 1721 and ERF E8.21 on torque, but these are good figures from 5.95 litres.

Our test vehicle was fitted with Mer cedes' own G4/65-6/9.0 six-speed gearbox. Available options are either a sevenspeed or six-speed splitter box, also from Mercedes.

So what does the extra power and torque mean on the road? As expected, bold acceleration figures: it's notably quicker

than our 1988 test of the 1617. Compared with the more powerful vehicles in our comparison chart it is certainly not the quickest; but neither is it disgraced.

Acceleration and hill-climb times are roughly on a par with the ERF E8.21, but cannot match the Cargo 1721 — admittedly fitted with a full aerodynamic bodykit — or the Volvo FL617 in more conventional trim, Mercedes has upped the gearing in the 1720 with a 4.3:1 fmal-drive ratio, as opposed to 4.75:1 for the 1717.

This, presumably, is designed to give the right mix of performance and economy, which appears to have worked reasonably well. As the sawtooth diagram shows, the six-speed box has a well chosen set of ratios, allowing the 1720 to cope well enough on the hills compared with its eight-speed rivals.

The gearbox has a notchy but comparatively light action. Clutch effort seems on the high side though, with a 32kg shove needed to push the pedal down and 25kg to keep it there.

The 1720 struggled to match its claimed gradeability by restarting on a 25% (1-in4) incline, but it finally made it, with a generous helping of revs.

Our noise meter showed that the 1720 was a bit louder than the 1617, but it is still one of the quieter cabs in our comparison chart. Subjectively noise levels were not obtrusive even at motorway speeds, making the 1720 a relaxing vehicle to drive for long periods.

"Under most operating conditions the 1720 is expected to return over-the-road fuel consumption figures matching the less powerful 1617s." So claims the MercedesBenz press release. Our Welsh test route has a representative mix of motorway, dual carriageway, hills and single carriageway roads to put this claim to the test.

Overall the 1720 returned 24.781it/ 100km (11.40mpg), compared with 22.61it/ 100km (12.5mpg) for the 1617 in 1988. Round one to the 1617.

Compared with the other higher powered 17-tonners in our comparison chart, only the Cargo 1721 is significantly better at 21.66lit/100km (13.04mpg), but it had the advantage of a full aerodynamic body. The FL617 just squeezes ahead with 24.61it/100km (11.50mpg) and the E8.21 falls behind with 25.491it/100km (11.08mpg). Hardly significant differences, of course.

We recorded better fuel consumption on the motorways 23.671it/100km (11.94mpg) than on the A-roads 25.891k/100km (10.90mpg). Normally this situation is reversed. Returning to our listed rivals, the aerodynamic bodied Cargo 1721 is the only other vehicle to achieve this. Since Mercedes is pitching for motorway trunking operators with the 1720, our figures suggest they have got the gearing right for the job.

On the road there was no suggestion that the chassis lacked stiffness, so Mercedes' claims for its slimmed down chassis seem to be reasonable. Our test vehicle was the 1720L, equipped with rear-axle air suspension, which no doubt contributed to the good ride and handling. Suspension movements were firm but well damped. Our test truck was also fitted with the optional ABS and ASR anti-lock brakes and anti-skid systems. The brakes pulled the 1720 up quickly and without drama in our brake tests; its stopping distances bettered only by the Cargo 1721 amongst our selected rivals. There was no trace of locking throughout, but the pedal had a longish movement and felt a bit spongy.

We drove into light snow once we left the M4 in Wales, and around Hereford the roads were damp and muddy. The ASR system uses the ABS circuitry to detect slip at the driving wheels. It will then brake the slipping wheel and also back off the throttle until traction is restored if necessary. If it were activated during our test it passed undetected, but it's a reassuring feature over slippery surfaces.

The handbrake, now operated by a lever to the left of the steering wheel, coped with the 25% (1-in-4) gradient facing up and down hill, so it should not give any cause for concern on hill re-starts.

Drivers familiar with the 1617 will notice some changes inside the cab. The dashboard has been completely redesigned, using the trim fitted in other Mercedes trucks. As mentioned earlier, the handbrake lever has been re-sited to the left of the steering wheel. Heating and ventilation is now controlled by rotary switches.

Unfortunately the 1720 has the single column stalk that afflicts other Mercedes trucks, and the sooner it's dumped the better. We would rather see one stalk for lighting functions and another for washers and wipers. Flashing the headlights when trying to operate the screenwashers earns strange looks from other road users and can be very irritating at times.

Nice touches include standard heated door mirrors which were helpful in the cold, damp weather of our test. Our 1720, was also fitted with the optional electric. passenger side window. Another switch on the dash cancels the ASR system, although having the benefit of ASR it might seem strange not to use it.

It should be possible for drivers of all shapes and sizes to find a comfortable driving position. The standard seat is adjustable for reach, rake and height and the steering column for reach and rake. Air-suspended seats are optional, but the standard seats fitted to our 1720 were still comfortable enough after a day at the wheel.

The M-type sleeper cab provides extra stowage space on the rest bunk; there is a large lockable bin between the seats and another in the overhead console for documents, in addition to large pockets in each door.

Mercedes' network of 86 dealers in the UK means you shouldn't have to travel far to find one. Most routine checks can be made with the front grille raised; with the cab tilted access to the main engine components is good.

As our fuel consumption figures show, the 1720 is most at home on the motorway. Under those conditions, it comes closest to fulfilling Mercedes' claim that its fuel economy is similar to the 1617. On the motorway the 1720 returned 23.671it/ 100km (11.94mpg), compared With 23.541ft/100km (12.0mpg) from the last 1617 we tested. It also compares well with other higher powered 17-tonners.

Against this is its price. At £35,660 (exVAT) for the chassis-cab it is around £1,300 more expensive than its nearest rival, the Cargo 1721. Opting for the 1720 rather than the 1720L and sacrificing the rear air suspension makes it a much more attractive proposition, bringing the price down to £32,960 (ex-VAT). That still makes it the second most expensive truck in the bunch, but by a much reduced margin. The E8.21 costs £32,370 (ex-VAT), while the lower powered Leyland Daf FA60.180 is also the cheapest at £30,920 (ex-VAT).

The eventual success of the 1720 will depend on operators being prepared to pay a premium for a more powerful truck, especially when congestion is quite likely to negate the potential for faster journeys.

Judged on its merits, Merc's latest high-power 17-tonner is a good truck with plenty of driver appeal. The three-pointed star will guarantee that it sells, and resells but we suspect that at a time when everyone is cutting their costs wherever and however they can, its lower powered 1717 stablemate will find greater fleet favour.

Llby John Kendall

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People: John Kendall
Locations: Hereford

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