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This year's Commercial Motor Sleeper Cab Test was more exhaustive (and exhausting) than ever before, covering eight different models and two countries. We took three cabs (ERF, Iveco and Volvo) to the MIRA proving ground as usual, for noise and ride quality tests, and a night's sleep in the bitter cold of February. Then CM was invited to Holland—and even colder weather—for a look at seven top-spec cabs in conjunction with our colleagues at Dutch magazines TTM and Truckstar. The Iveco and Volvo cabs took part in both parts of the test.
The MIRA tests were similar to previous years. We measured and photographed each cab, assessed their heat and noise insulation and measured their ride quality, finishing by spending a night in the bunk.
The Dutch tests were a little different: after taking compre
hensive measurements, including noise intrusion tests, we tried to stow a "shopping list" of articles in the cab the things a driver might take on a two-week trip away from home.
The piece de resistance was the mattress-sniffer: Dick Kroon, product manager of Royal Auping, the Netherlands' biggest bed manufacturer. He took a good look at the seven vehicles in Holland, examining each bunk minutely—and he could tell the type of mattress foam from its smell alone! Kroon was very critical of most trucks' sleeping arrangements, as you'll find out on page 26. We used a diesel compressor as a noise source to test the sound insulation: this unsilenced relic produced an impressive 109dB(A) at a metre. Each tractive unit was backed up to the compressor and then noise measurements were taken inside.
The Dutch tests were similar—though not directly comparable to the UK figures—using a 110d8 generator placed in roughly the same position as a trailermounted fridge unit.
Given that the human ear cannot detect a difference of less than 3dB(A), there is little to choose between the noise intrusion figures—except to note that the Volvo and Scenic were both very well soundproofed. Onroad tests at MIRA showed up more of a difference. The lveco was noticeably noisier than the Volvo, with the ERF between the two.
As usual we assessed the ride over a smooth road and over broken concrete, using MIRAs ride meter, This has accelerometers placed under the driver's feet, on the seat squab and taped to the seat back. The first two measure vertical acceleration, the third the longitudinal (fore-and-aftl forces.
We've also calculated a ride index, giving an overall view of the figures—the lower the number the better the ride.
The Volvo and lveco Ford's figures are practically the some on the smooth road—the ERF's figures are around 20% worse. But the subjective results are altogether different.
While the computer can differentiate between the trucks on the smooth track, drivers will struggle to tell them apart. The only exception was the Volvo's tendency to wallow over longer undulations.
Over broken concrete, the three trucks couldn't be more different. The Volvo's suspension prevented any major jolts getting through as we Passed over potholes, but small bumps caused the cab to jiggle around. The opposite was true in the lveco: it allowed major shocks through, but controlled the smaller bumps extremely well.
The ERF didn't allow potholes or minor road blemishes to shock the driver but it did this by subjecting the driver to slow, large amplitude movements. Over broken concrete, the driver's seat moved so much that it was difficult to hold the accelerator at a constant speed The driver wasn't subjected to violent acceleration—which is why the figures ore close to those of the Volvo and Iveco Ford—but that floating feeling could be disconcerting on smaller roads.
We first took the cab interiors down to more or less ambient temperature (around 5°C at MIRA) by simply opening the windows for a couple of hours Then—with windows, doors and vents firmly shut—the cab heater was switched on at full blast for two hours. We recorded the temperature in the cab at that point, then shut the cab up again and left it empty to see how much heat was lost overnight.
The lveco's complex-looking heating system worked well, though it didn't reach the withering 27`C of the Volvo's unit—it is programmed to peak at 25°C
The ERF's heater had a temporary problem which limited its peak temperature to 21'C, but its insulation performed impressively. In Holland, we did a similar thing with the new Scania cab. Unfortunately, the insulation test was not cornparable, as the overnight temperature dropped to a brass-monkey -.3"C. But the heater recorded a maximum temperature of 28°C from an initial 3'C—a terrific output.