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Britain perms for the 3S•tonner
Page 81
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Graham Montgomerie weighs up the odds
IF BRITAIN ever decides to opt for a higher gross weight limit, what will be the effect on truck and trailer design ? To find out what problems would be involved and how the manufacturers would get round them I spoke to Mr Michael Dunn, chief engineer, heavy truck engineering, Ford of Europe, on the truck side and to Mr John Crane, technical director of Crane Fruehauf, for the trailer viewpoint. As a starting point we assumed an increase in gross weight to 38 tonnes (!). The minimum horsepower requirements would be in the region of I72kW (230bhp) if the existing power-to-weight recommendation of 6bhp/ton continues. Thoughts that this might be raised to 8bhp/ton to fall in line with Germany were quashed when that country reversed its thinking and returned to six earlier this year on grounds of economy. Hard on the heels of this announcement came Italy's decision to go to 8bhp/ ton, possibly because of Fiat's vast capital investment in the new and extremely powerful V8 engine range.
More bhp
Mr Dunn believed the 6bhp/ ton requirement was inadequate for a 32-tonner but could be acceptable for a heavier combination as the power-toweight ratio requirement varied with gross weight. Thus the bigger the vehicle the smaller the ratio could be. For example, a 38-tonner would be quite happy at, say, 7bhp/ton, but a light van operating at the same ratio would be a mobile traffic jam. So far this factor had not been allowed for in legislation.
It would, perhaps, be an idea In the opinion of Ford, five axles is the best bet for running al 38 tonnes gcw. This particulal model is a 6x4 Transcontinenta powe,-ed by a 265kW (355bhp1 Cummins engine.
to compare acceleration figures for vehicles at various gross weights. Feasibility studies would seem to indicate that a power-to-weight ratio of 6.8bhp/ton was the optimurr which on conversion to metric units would give a figure of around 5kW/tonne.
Power outputs will 1:1( adequate from most of thE existing engines, but an in crease in weight will mear that trucks like the Leykuk Buffalo and Volvo F86 wil still be limited to 32 tons.
The heavier trucks in them two manufacturers' range, th* Marathon and the F88 respec tively, have power output well in excess of the minrimun requirements whether the in crease be to 38, 40 or 44 tonnes.
The official Ford viewpoin on gross weight limits wai that an increase was neede< very definitely over the presen 32-ton line and that 38 tonnei