Daimler Roadliner/Plaxion 50-seal service bus
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EWER since Daimler introduced the Roadliner in 1964 fitted J-Li with the Cummins V6 200 diesel engine for single-decker use, operators wondered what the performance and fuel consumption would be like comparing it with a similar type of vehicle fitted with an in-line engine.
The coach version of the Roadliner was road-tested by COMMERCIAL MOTOR in August 1966 and this very favourable report probably answered any doubts regarding the engine.
Tilt service bus version of the Roadliner was road-tested recently and because the gross weight was 1 ton 3 cwt less than that of the coach, fuel consumption figures were better. Braking was good, even though when the coach was tested the weather was wet which did not do justice to the brake stops. Acceleration figures for through-the-gears at speeds up to 30 m.p.h. were 2 sec. faster on the bus, but for speeds above that figure the extra 57 b.h.p. and higher ratio rear axle of the coach enabled it to reach 40 m.p.h. in 2.5 see, less time than the bus.
The Roadliner used for the test had 9,000 miles on the clock and was one taken off service and loaned for the occasion by Potteries Motor Traction, Co. Ltd. Stoke-on-Trent. Certain changes have been made to the service bus, some of which are manufacturer's changes and some to user's specification. The model tested is one of an order for 24 and instead of air suspension as used on the coach has Metalastik toggle link rubber suspension on the front and rear axles—the first service buses to use this suspension which was developed by PMT in conjunction with Daimler and the Midland Red Bus company.
The radiator is now fitted at the rear beside the engine, dispensing with yards of plumbing previously required, which was a headache if a water leak developed.
The engine has been derated to Daimler's specification of 135 b.h.p. at 2,050 r.p.M. which is in keeping with similar single-decker buses. Instead of the electro-pneumatic gear selection the bus has air assisted selection, this again being the user's choice. The rear axle has a single speed unit fitted, in keeping with service bus practice.
For the test the Roadliner was loaded with sand bags representing passengers' weight which, added to the unladen weight plus that of myself and two observers brought the gross vehicle weight up to 11 tons 13 cwt. Full-pressure brake stops were made and stopping distances of 18 ft. 2 in. from 20 m.p.h. and 44 ft. 10 in. from 30 m.p.h. show that the Roadliner service bus is well within requirements with the air-pressure system having two circuits fed from a reservoir through a dual brake valve. The handbrake is a single-pull type and is air-assisted.
Because of the difficulty of finding a suitable road to carry out the brake tests which are done with the vehicle fully laden, it was decided to carry out these tests at the Motor Industry Research Association test circuit at Lindley, Nuneaton. The very good figures to be seen in the specification panel were obtained on dry tarmac with a good adhesion character. There was little marking of the road and never at any time did the wheels lock.
All brake applications resulted in smooth progressive stops with no wallowing of the body, plus no pull either way. From 20 m.p.h. a handbrake pull returned a Tapley reading of 32 per cent. Probably due to the effective stops made with the footbrake, the time taken to bring the bus to a complete halt with the handbrake applied seemed somewhat long. So it was decided to try another two stops, where again a 32 per cent Tapley reading with no roll-on or bump which could affect the reading confirmed that the stopping distance was acceptable.. Before moving on to the fuel consumption tests, use was made of the test slopes or humps at MIRA to assess handbrake effectiveness and to check gradient ability. The hump has two sides, one having a 1 in 5 and the other a 1 in 6 gradient. Going up the 1 in 5 the Roadliner was stopped in the middle section and the handbrake was applied. This held the vehicle comfortably with a straightforward restart in first gear being made. Travelling over the top and stopping in the centre section of the 1 in 6, a reverse start was made very easily. This procedure was reversed and a stop-and-restart test was made up the 1 in 6.
The fuel consumption runs were made on a route through Meridan on A41, then by A452 to the Stonebridge roundabout which served as a halfway turning point. On the non-stop unladen test where the speed of the Roadliner was kept down to 30 m.p.h.,
18.6 m.p.g. was returned with the same run half-laden producing 14.9 m.p.g. Two stops per mile half-laden and two stops per mile laden over the same route produced fuel consumption figures of 11.6 and 11.5 respectively which shows the economy of the vee engine because although there was a weight difference of I ton 12 cwt. between the laden and unladen stops there was only a drop of 0.1 m.p.g.
Due to traffic congestion it was impossible to carry out the six stops per mile laden test but this was carried out at MIRA. Again the speed of the Roadliner was kept to 30 m.p.h. producing a fuel consumption figure of 8 m.p.g. against a figure of 6.15 m.p.g. for the coach, tested over the same route, which for a vehicle grossing almost 12 tons is good.
Acceleration tests showed the Roadliner to have a road performance equal to if not better than similar single-decker buses tested. The through-the-gears tests were carried out effortlessly due to the excellent gear change. The gear pedestal could have been brought nearer to the driver's left thigh but after inquiries I found the position was specified by PMT.
The bodywork is by Plaxtons and entrance to the 50 seats is provided ahead of the front wheels by means of a 1 ft. 2 in. step with a second step which allows access to a step-free gangway running the full length of the bus. The only criticism which could be made of an otherwise excellent vehicle was that during all the various tests the doors would not stop rattling and on one occasion when I stood by the doors there was a draught which should not have been present. Travelling over uneven surfaces unladen there was a slight shake from the suspension.but in both the unladen and laden condition no bumps whatever were felt.
Slightly irritating was the noise from the demister motor although with the engine and transmission located at the rear, riding at the front is very quiet compared to a front-engined bus, therefore any noise however small it may be sounds extra noisy.
The driving compartment is partly but not completely isolated from the main body of the bus and after spending two six-hour driving spells in the driver's seat, no arm or leg aches were experienced due to the very comfortable driving position—in fact this vehicle appears to be the nearest approach to a p.s.v. with private car handling.
Visibility from the Roadliner's driving compartment is excellent, probably due to the windscreen's bottom edge measuring only 4 ft. 8 in. to ground level. Air is used for many applications on this vehicle and on one occasion it was necessary to use the airoperated windscreen wipers. By slightly turning the switch it was possible to allow a tiny trickle of air to reach the motor because the water content on the screen did not justify the wipers working at full speed, which with certain types of wipers cannot be controlled. Mirrors were well-placed including an interior one which is a useful fitting.