RESULTS
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• Only one litre of fuel after more than 1,600km separated the two leading contenders in our 38-tonne economy run last summer. We expected the results of this 17-tonne exercise to be even closer — and we were not disappointed.
In this case a mere 1.44 litres (only 23' pints!) came between the trucks in first and fourth place, which serves to justify the extreme lengths we went to to ensure accuracy and fairness in all our measurements. It was for this reason that no results for the MAN appear on these pages. A minor navigational error meant that the truck did not cover exactly the same terrain as the other vehicles, and unfortunately this led to the MAN's withdrawal.
This was especially disappointing because the MAN seemed to be well up with the pack, but there was no alternative since we had no way of ensuring the results were comparable.
One of the reasons for encouraging entries in two power categories was to see whether the more powerful engines brought with them a penalty in fuel consumption.
The results show quite clearly that, given an appropriate choice of gearing, that the reverse can be true. The most economical truck, the Volvo FL617, came from the higher power class, while the three vehicles giving the best blend of performance and economy — the Volvo, the Mercedes 1720L and the ERF — all boast lusty charge-cooled engines.
Indeed, what this and our other recent economy events have shown quite clearly, is that the latest charge-cooled engines have no equal when it comes to efficiency.
This argument tends to fall down slightly when it comes to the AWD, but the TL 17-27 was handicapped by gearing which was clearly designed for drawbar operation at 30 tonnes plus. With a higher back axle ratio the AWD might have thrown up some interesting results.
Getting back to the fuel consumption results, the two trucks without charge-cooling were certainly not disgraced: the lower powered FL617 returned superb fuel figures, but at the expense of journey times, and the Mercedes 1717 combined decent speed with a modest thirst.
Our productivity awards are designed to reward not only the driveline's ability to turn in good fuel figures with a decent turn of speed, but also to recognise the benefits of a low chassis weight, with the advantages in payload potential that implies. A net payload of 10 tonnes has always been a benchmark figure for 17-tanners, so it was interesting to see that three trucks exceeded this by a useful margin — the Foden and both Volvos — while the AWD and the ERF came extremely close (for the record, the MAN also just beat it).
This leaves the two Mercedes open to jibes about heavy German chassis, but in truth neither vehicle had been specified with any concession to weight saving, and the inclusion of the air suspension on the 1720 is a prime example of this,
The Volvos in particular demonstrate the opposite philosophy, and the obvious thought given to weight saving on the duo shows what can be achieved with comparatively simple and inexpensive modifications.
Not surprisingly, therefore, their low kerbweights gave the two Swedes a head start in the productivity stakes, and with its event leading economy and acceptable speed it came as no shock when the charge-cooled FL617 also carried off the productivity awards both overall and in its class.
It was pushed hardest by the winner of the lower powered class, the ERF E6.21, which made up for its heavier chassis with its superior pace across the ground.
The lightest truck of the eight, the Foden 2250, was also the fastest, but by pushing on with less attention to the fuel used, its overall productivity figure suffered in comparison with the best of the rest.
Taken in isolation, the average speeds around the route are more a reflection of driving style than available performance. The only noteworthy variations were the less powerful Volvo, which was perhaps struggling against rather high gearing, and the AWD with the ERF which, with nine-speed gearboxes and powerful engines, were usefully quicker over the hilly stuff on the last afternoon.
The other measure of vehicle and driver performance available to us was the number of gearchanges made on the route, and while the figures quoted cannot be considered to be exact, they do give a goad indication of the trends.
Most drivers made around 600 changes on the route, and in general terms the more powerful trucks used slightly fewer shifts, and the less powerful vehicles somewhat more. The main exceptions are the fast moving Foden, which used by far the most shifts in an effort to maintain momentum, and the Mercedes 1717, which combined sensible gearing and steady driving to return by far the lowest total of changes.
0 Our special thanks for making the run possible to: Stan Thomas, TNT, Boalloy, Lucas Kienzle, Mobil, Warwickshire County Trading Standards and Simpsons of Great Yarmouth.