High limits hit economy
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ONE IN FOUR commercial vehicles sold in Britain falls within the 7.5 tonne category. Compare this to the one in 20 sold 10 years ago, and it is not difficult to see why manufacturers consider this sector so important.
The rise in sales can be traced directly back to the changes in legislation in 1976, which allowed car licence holders to drive goods vehicles up to 7.5 tonnes gvw. Of the 35,000 UK light truck operators most have fleets of five or less, while 70 per cent have only one vehicle. The vehicle hire compa n i es are the biggest operators at 7.5 tonnes.
CM took five vehicles from this important sector around its 210-mile Welsh test route for medium-weight vehicles to find out how they measured up against each other.
In March this year changes in 7.5-tonne gvw speed limits set light lorry manufacturers with a task most would have preferred not to tackle — how to get good fuel economy from faster vehicles. With the maximum motorway speeds raised to 70mph (60mph on dual carriageways), fuel economy has taken a nose dive.
An indication of how much the revised speeds have affected fuel consumption was most clearly shown by the MAN-VW 8.136 we tested. At the old speeds the 136bhp en gined 8.136 returned 14.8Iit/100km (19.05mpg) when we tested it in 1981. That, we said, "put it near the top of the table for 7.5 tonners".
Three years on, running at the higher speeds the 8.136 could manage only 19.31it/100km (14.6mpg) despite being fitted with the same specification engine, gearbox and rear axle.
The right driveline combination, and in particular rear-axle ratios, has become vital to fuel economy at 7.5 tonnes. Engine horsepower, too, remains important, although Ford, which holds a massive 41 per cent share of the 7.5-tonne market, is unconvinced of the need for the 130hp-plus engines offered by manufacturers such as lveco, Mercedes, MAN-VW and Bedford. The results of the 0811 around our test route would seem to back up its argument.
Ford claims that the only operators likely to derive any real benefit from these bigger engines at 7.5 tonnes are those running with high box bodies, and they will only gain in improved vehicle speeds rather than higher fuel economy.
A good example of the correct engine/driveline equation appeared almost by accident during our tests. Although putting in a 135bhp powered 79:14 with a 4.55:1 rear axle as its "official" group test vehicle, lveco also ran a lower powered 79:10 with a 94bhp engine and 4.18:1 axle around with it. While the 79:14 could only manage 15.1mpg, the 79:10, using the same tank top-to-tank top refuelling procedures overseen by CM achieved 17mpg.
Three manufacturers were noticeable by their absence in our group test. Leyland "did not have a Roadrunner available", which considering all the ballyhoo of its launch was something of a surprise. Mercedes-Benz declined to enter (although a full road test on the 7.5-tonne 814 can be found in CM Oct 6 1984). Bedford was simply unlucky. Its TL860 developed engine trouble at the last moment.