Trying the PRI00—• Berliet's latest city bus
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by Gibb Grace
THE MAJORITY of the buses running in French cities are Saviems — and Lyon, despite the fact that it is the home of rival Berliet, is no exception. Berliet is naturally. keen to change this pattern and as this city's existing fleet reaches retirement age it is odds on that it will be replaced by Berliet's newest city bus, the PR100.
This model has a structure of a type unknown in Britain but which has been popular on the Continent for some years. The chassis-less structure allows a low floor height but cannot be described as truly integral like that of the Leyland National; the chassis and body are built up from square-section tube and clad with aluminium and glassfibre panels. Visually, the PR100 is attractive despite its almost vertical sides; the front-end styling is unusual because of the deep quarterwindows but ib very functional. A useful cost saving of the design is that the deep, flat screen is used upside-down as the rear window.
Floor level is just 2ft lin. above ground level and flat, apart from front and rear wheel boxes and a raised section over the rear-mounted engine.
The standard engine used is a Berliet-built 6.92-litre V8 diesel which produces 170 bhp at 3000 rpm and 350 lb ft torque at 1700 rpm; the Perkins V8-510 is an option. The drive is taken forward to a Wilson HVD 60 gearbox which is offered in fully automatic or clutchless manual selection form. Gear ratios are 4.74, 2,64, 1.66 and 1.00 to 1 forward and 5.2 to 1 reverse. The Pont a Mousson hub-reduction drive axle is available in three overall ratios of 6.82, 8.20 and 9.33 to 1, giving approximate top speeds of 50, 43 and 37 mph respectively at an engine speed of 3000 rpm.
Proving route To try the PRIO0 in its own environment CM used Berliet's own bus proving route in and around Lyon, in South Eastern France, which has been designed tO test all aspects of the vehicle. Lyon, like so many cities, has grown continuously from small mediaeval beginnings and now has a population approaching two million spread over a very large area.
The first part of the test route, taking us through the old town of Lyon which is built on the side of a steep hill, included one climb that is barred to the current city buses because of its severity. The road climbs the alpine-style hill complete with hairpin bends and crosses and recrosses a sunker with an even steeper gradient whicl straight up the face of the hill — tF were told, was originally used for a c tram track.
Although loaded with 6 tons 12( payload {the equivalent of 100 passe and grossing a little over 15 ton PR100 coped with these hills and corners admirably. Speed was restrici the narrow road and other traffic as as anything, but even so on a 1 in 10 s of hill 20 mph was possible in third gel We had missed the early morning r traffic but the streets in the old town w narrow that even a badly parked van c a jam. We were not making scheduled on the route but over this section at we were compelled to make many st( traffic. An indication of the ti conditions is that we covered only miles in the first hour. Soon after leavil old town we dropped down a steep wi road to the river Soane which we followed out along the wide N43 Neuville, a small town eight miles fro) centre of Lyon.
From Neuville the route took us into Lyon, the relatively wide, quiet ra the way into the city being an ideal pla(
take over the wheel. I was tely impressed by the excellent to the rear, by large external and mirrors to the front, through the p screen and to the kerb through :nger door.
ig the PR100 could not be simpler; a matter of selecting the right gear ring correctly. The only vice I could as a slight jolt as a gear-change was ractice might have cured this but in trying different techniques with the nd amount of throttle, I was unable J. it in the time available.
nsion combination suspension is a very effective rtion of steel spring and air. Coil are used for the independent front on in conjunction with low-mounted es and conventionally mounted leaf at the rear. These steel springs are l to suit the unladen bus while the ings are designed to cater for whatever passenger load is carried. In this way the entry level of the bus and the ride frequency remain the same regardless of how many passengers are carried. The steel springs themselves are soft in order to provide a good ride; to control roll and exaggerated bounce, anti-roll bars and double-acting dampers are fitted to front and rear suspensions.
The ride on smooth asphalt surfaces was as near perfect as I have experienced in a psv; there was neither perceptible roll nor pitch and nothing one could call bounce. On rough asphalt or cobbles there was a certain amount of thud and slap from the wheels but surprisingly little body movement.
By comparison with these excellent standards the noise level was disappointing: the engine was smooth but produced a discernible amount of noise to which the axle and bodywork also contributed. It is fair to point out, however, that the vehicle was largely untrimmed, being a test model for a large Polish, order, and was
considerably modified internally with racking which carried the sandbag payload at the correct height.
Tight bends posed no problems owing to the good between-kerbs turning circle of less than 601t; the steering effort required for the ZF power-steering was low, but unnecessarily low-geared at nearly six turns from lock to lock.
The low gearing, however, did not detract from the straight-ahead steering as there was no free play at the wheel.
Neat and simple On the good near-empty road back into Lyon the PR100 ran at the legal speed limit of 60 kph (37 mph), which was also its own top speed with the 9.33 axle, without fuss. Slowing down in traffic was very smooth, as the initial brake pedal movement automatically brought the Telma retarder into action. If the Telma alone was not sufficient, further movement of the pedal brought in the service brake in the normal way. I have driven several vehicles fitted with a Telma retarder, including coaches, but this is the neatest, simplest application of Telma I have yet come across.
Because of the run out to Neuville and back, we just covered over 22 miles in the second hour's driving and thus increased the overall average speed.
The return route took us mainly through the suburbs and missed the heavier traffic of the city, the average speed for the whole of the 41-mile route working out at 16.7 mph. Fuel consumption for the run worked out at 6.8 mpg. While this fuel consumption would be considered high by British bus operators, I think the Berliet's average speed and certainly the payload, was higher than is common in UK urban running.
On Berliet's test track we checked the acceleration and braking of the fully loaded PR100. Acceleration to 20 and 30 mph took 19.1 and 34.4 seconds respectively, which is adequate rather than startling. Measurements taken on a MotorMeter brake tester showed the stable deceleration to be 0.75g from 20, 30 and 37 mph (maximum speed) which is very good for such a heavy vehicle. The secondary system, which works on the rear axle only, produced 0.27g deceleration, and a Berliet engineer told me this was below par and that 0.30 to 0.35g would be normal on a production vehicle. It was noticeable that even under these maximum deceleration conditions the vehicle showed no tendency to pitch.
To sum up, the PR100, though not as structurally advanced as some, is a very good bus by any standards and has some features such as its ride and driver's visibility that set standards by which the competition may be judged. Important too, I think, is the styling which, thougl unusual is very functional but at distinctive. When Lyon gets i PR100s the passengers will not be doubt about what make of bus is city's roads.