Road Temr
Page 32
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Forty mph equals an engine speed of 1,200 rmp, at which point maximum torque occurs, but it proved willing to pull down to 1,100 rmp and less. Apart from the fuel stop on the M6, I changed down using the split on 8th gear just three times. The first time at Keel where we were baulked by slower traffic, and then not again until Brough and Shap. At 60 mph the engine turns over at a sedate 1,800 rpm.
Weather conditions on the first day, wet with strong winds, were far from conducive to economical fuel returns, and, on comparison, it did not do so well over this stage where the air flow equipment might have been expected to show its worth. It was over the slower and sometimes hillier parts of the route that it consistently returned better fuel consumption figures than earlier vehicles tested at this weight. Only the ERF, powered by a Rolls-Royce 290L engine, gave a better fuel performance over the undulating Al, out of the remaining sections. Perhaps the most exceptional performance for the Mecedes 1638 was between Rochester and Nevilles Cross, over the hilly A68, where a fuel consumption of 48.5 lit/100km (5.8mpg) was recorded. Hill climbing is certainly no obstacle to this vehicle as times for the recorded climbs reveal.
The steepest gradient at Consett was instrumental in showing the shortcomings of this ZF gearbox. Fast downchanges through the detent from high to low range are just not possible. Slow to learn and perhaps unused to my right hand changing gears in this left hooker, I managed to beat the system on at least two occasions, and without trying finished up without any drive in the selected gear.
All the controls are extremely light, which I welcome with the foot pedal, but I found it unnerving being able to steer with just my little finger on the steering wheel.
The double H gate may be too wide for some but I liked it, along with the bias towards 1st and 2nd or 3rd and 4th slots.
Engine speed is governed electronically by 300 rpm in the top half of the gearbox to just under 2,000 rpm. When maximum revs are reached, a further rise is prevented by the injection pump governor. If traffic conditions require extra speed in one of the ratios between 5th and 8th (it is difficult to imagine just when this might be), the driver can override the limiter by kicking down on the accelerator.
Soft springing gives a smooth ride, and for the driver an automatic air suspension removes any of the few road shocks remaining.
The exhaust brake working on both manifolds seemed to work well, but on the slower, steeper hill descents, liberal use of the foot brake was needed. Just b fore Shortley bridge, I notice that the comparatively Ian trailer brakes were smoking.
The cab is fitted with plain ru, ber mats in the foot wells; t1' remainder of the trim is lush. sunshade over the windscreE protects the driver's eyes. Ai gled lamps in the roof give goc illumination to where neede, Storage areas include cubb, holes over the screen, an exte nal equipment locker and an ii ternal wardrobe. Additioni storage space is availabl beneath the twin bunks locke behind the seats.
Steering wheel and drivin seat are adjustable to suit th dimensions of all manner ( driver shapes and sizes. The pa: senger side window and bo1 external mirrors are ontrolle electronically from a centr control within the cab.
The cab roof on the asseng( side is raised slightly to give little more freedom en dre: sing or preparing for a night sleep. No measurem nt of i, cab noise levels was recorde but it may be suffici nt to sk that, with effective ins lation 131 tween the driver and e gine, it very quiet. With the cab tiltE forward to give 70 degree access is provided to he pow unit and reveals the elescop gearlinkage, avoiding holes the floor pan, and the i tercooli located well forward.
Two large front f aps gir access to daily service joints.