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Whispering Latins on trial

10th December 1976
Page 58
Page 58, 10th December 1976 — Whispering Latins on trial
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AT CM we have carried out full operational trials on both the 0M55 and 75 vehicles from Fiat-the former in integral van form and the latter fitted with an all-steel drops ide body. On both occasions the Commercial Motor Midlands test route was used to evaluate the fuel consumption.

In its integral van form the 55 had a loading volume of 12.3cum (439cuft) and for our test it was loaded to 5.47 tonnes (5 tons 8cwt) gvvv, giving it a test payload of 2.5 tonnes (2 tons 9cwt). The wheelbase was 3.0m (9ft 10in) and the rear axle ratio was 3.545 to 1.

The fuel consumption was found to vary surprisingly little with different road conditions. The best stage figure we recorded was 11.7 lit/100km (24.1mpg) on the A-road section between Minster Lovell and the finish of the test route at Hemel Hempstead, while the worst figure was the motorway result at 12.1 lit/100km (23.3mpg).

When these figures are compared against their individual average speeds of 44.6 and 84.5km/h (27.7 and 52.5mph) respectively, it can be readily appreciated what little difference there was in the fuel consumption even at widely varying road speeds. The overall figure for the 312km (194-mile) test route was 11.9 lit/100km (23.8 mpg).

With this rear axle ratio, the maximum speed of the 55 van was 105km/h (65mph). Acceleration performance is very much dependent on wind direction with this type of body and the Fiat proved no exception. On the horizontal acceleration straights at MIRA the time taken to reach 50mph varied from around 50 seconds with the wind to over 63 seconds against it.

With its engine output of 63kW (85bhp) the 55 pulled well in all the gears even from very low engine speeds. Accelerating from around 10mph in the direct drive top gear was possible even though at this road speed the engine speed is below tickover. It did not feel particularly happy about this until a road speed of around 25mph had been reached, but it proved it was possible.

The vacuum/hydraulic service brakes were consistent on the braking tests with average retardations in the region of 0.75g being recorded at all the test speeds. The required pedal pressure was not excessive and the Fiat pulled up in a straight line on every stop. In fact we recorded a peak efficiency of 0.86g during these tests.

This good performance was repeated with the mechanical park brake, which gave a maximum retardation figure of 41 per cent. On the hills, it held the fully laden vehicle on a 1 in 4 gradient with no difficulty.

A few laps of the MIRA ride and handling course did not disclose any idiosyncrasies as the Fiat rode the camber changes very well with little body roll, even allowing for the low centre of gravity of the test road.

As far as manoeuvrability was concerned we recorded turning circles for this model, between kerbs, of 11.4 and 11.6m (37ft 4in and 38ft Oin) for left and right lock respectively.

At 7.5 tonnes (7.38 tons) gvw the Fiat 0M75 just comes into the nonhgv category as far as drivers' licences are concerned. The major mechanical components are identical to those of the 55, including the engine which gives the heavier machine a power-to-weight ratio of 8.2kW/tonne (11.4bhp/ton) at the full gross weight.

When we tested the 75, the steel drop-side body permitted a maximum payload of 4.37 tonnes (4 tons 6cwt) for a gross weight of 7.49 tonnes (7 tons 7cwt). Over the same Midlands test route, the heavier Fiat achieved an overall fuel consumption of 14.6 lit/100km (19.4mpg). On the middle section of the test between the end of the M45 and Minster Lovell, the 75 achieved the excellent figure of 13.3 lit/100km (21.2mpg).

On the motorway itself the extra weight compared with the 55 made its presence felt with a consumption of 16.7 lit/100km (16.9mpg) for an average speed of 85.9km/h (53.4mph). The rear axle ratio was 4.18 to 1 which gave the truck a top speed of 92km/h (57mph).

Although not achieving the very good braking figures of the 55, its heavier brother nevertheless acquitted itself well in this category by consistently returning a mean retardation in the region of 60 per cent.

On both these Fiat tests, the low in-cab noise level was much appreciated. Even when travelling at near maximum speeds on the motorway, conversation across the cab was easy.

• Graham Montgomerie

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