THE TESTS
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Our testing procedure is little changed from previous years. First, we looked at the driving environment in each vehicle, followed by a brief test drive to gain subjective impressions. More scientific tests were then carried out to assess noise levels and ride quality.
A noise meter is part of our standard roadtest kit and we assessed each vehicle as we would in a normal roadtest with in-cab noise readings at tickover, 80km/h (50mph) and 96ktn/h (60mph) to represent trunking and motorway running. We also tested each cab for noise penetration. If you can hear every time a sparrow coughs outside, the chances are you won't get much sleep in a busy truckstop.
For this test, we used a noisy diesel compressor, placed a set distance from each cab. We took noise readings outside at windscreen level, then inside the cab to see how much of the racket got through to the interior.
To support our subjective impressions of ride quality, we needed to assess how much cab movement is transmitted to the driver. The Motor Industry Research Association has developed its own equipment for this purpose and we applied the 909-1 Ridemeter to each cab in turn. Sensors are attached to the cab floor, seat squab and backrest, which measure the acceleration forces acting on them. This indicates vertical movement of the cab and vertical movement of the driver's seat to see how much cab movement is transmitted to the driver. The sensor in the seat back measures the fore-and-aft pitching motion of the seat — a good measure of how much cab nod gets through to the driver.
To obtain easily measurable results, each truck was driven at a constant 32Ian/ h round a section of track at MIRA which has a broken concrete surface. A total of three runs were made in each vehicle and the average reading calculated from the results. The lower the figures, the better the ride.
The only way to assess a cab's sleeper appeal is to sleep in it. Armed with maximum and minimum thermometers, we set out for Crickstop truckstop on the A5 and parked up for the night to assess comfort, space, insulation and heater capability.
Before turning in we fired up the cab heaters to measure how quickly each cab reached 21°C (70°F). Then the heaters were switched off and the minimum overnight temperature was recorded.