Comfort at Low All Round Cost
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By Laurence J. Cotton,
M.I.R.T.E.
TESTING the Seddon underfloor-engined passenger vehicle was far from being an arduous day's work, because, in addition to the luxury of the Plaxton Venturer body, the coach was notable for its silence and exceptionally smooth and
efficient suspension. Although the Plaxton body gives all the comfort of the " heavy " luxurious models, the low weight of the Seddon chassis promotes economy and with a 5klitre oil engine of high output, hillclimbing and acceleration make little difference to fuel consumption. Furthermore, the initial cost of the complete vehicle is under £4,000.
Ample Tyre Capacity
The Seddon passenger chassis, With: Perkins R-type engine mounted vertically amidships, provides a sound basis for a coach or bus. body. It his adequate power and, because of its reduced weight, is amply shod with 9.00-in. 10-ply-rating tyres without overloading at the front. This, in turn, is reflected in light control.
The engine, clutch and gearbox are conventionally mounted, a"sing Metalastik sandwich-type units at the front and Metacone bushes at the rear. As the R type is a relatively short-stroke engine, in comparison with the P-type unit formerly used, it projects only slightly above frame level and leaves working space at the sides.
A squat radiator, with a casing at the rear to form a cowl and carrying a spider for the fan bearing, is installed behind the front axle and a header tank is provided above the level of the engine. There is direct drive between the crankshaft and
B6
fan, and for operation in warm climates a step-up drive is available to increase the fan speed.
Drive from the gearbox is taken through a single propeller shaft having a Layrub joint with sliding splines, to an Eaton 16,500 two
speed axle. Fixed-ratio and twospeed axles are available, but the test vehicle offered ratios of 6.8 and 4.89 to 1, the higher ratio yielding a maximum speed of over 60 m.p.h.
To stop a 91-ton mass from that speed requires good braking, which is attained by employing components
similar to those used in the Seddon 8-ton overseas goods chassis. Pedal effort is lightened by a Clayton Dewandre 6.87-in, vacuum servo operating through Girling hydraulic equipment to two-leading-shoe units.
The frame is level from front to rear and is full-width to provide working space near the engine, but tapers towards the front to give clearance for a 62-ft. to 63-ft. turning circle. The suspension is soft but well controlled, the 43-in, front and 58-in, rear springs being helped by Girting shock absorbers.
In the Seddon-bodied bus the floor is ramped from the .front entrance and over the engine, the gangway height thus being comparable with that of other underfloor-engined models.
Fun Passenger Comfort
Seating in the Plaxton coach body is luxurious and interior trimming is well modulated. Side panels are of Formica and the roof lining is of Bryfex. There is no obstruction by wheel-arches and the near-side seat close to the central entrance has an overhanging platform to provide adequate foot" space.
Full-length tubular racks are provided for parcels, but the bulk of the luggage is carried in a 97-cu.-ft. rear locker, the door of which has a telescopic spring support. The test coach carried 10 cwt. in the locker to represent the baggage of 41 passengers, and the remainder of the load was distributed correctly on the floor.
As a complete vehicle, the Seddon coach is about 11-li tons lighter than its big-engined contemporaries equipped with a similar body, and on power-to-weight ratio, having an engine rated at 108 b.h.p. at 2300 r.p.m., it stands on an equal footing. The performance potential would, however, be misrepresented if the output of the 5i-1itre engine was regarded as nearly equal to that of a 9-10-litre unit, which, although governed to below 2,000 r.p.m. and rated only 20 per cent. higher in horse power output, would develop about 80 per cent. greater torque.
Obviously, the Seddon must be slower on hills, although a four-speed gearbox coupled with a two-speed axle effectively reduces the difference. The high-ratio two-speed axle put the fully laden coach at a disadvantage in the first section of the trials when negotiating a long gradient over the Pennines.
A short detour was made from the works at Oldham before starting hill climbing and I soon noticed the light steering effort, with only 3 tons 12 cwt. imposed on the front axle. What might have been difficult manceuvring with a heavy coach was accomplished without exceptional physical force when shunting and turning on the weighbridge, and although the chassis was new, the gear lever and other controls were free from stiffness.
Static brake tests had been made after an axle change on the eve of the test, but the coach had not been tried on the road. Final adjustments were made after the morning's work over the hills. • As a passenger I noticed the unusually good suspension, which provided smooth travel under all road conditions, and the general quietness inside the body. At the front, near the driver, the fan whine is noticeable to the practised ear; amidships there is a distant "rumble ",from the engine and the silencer note is more pronounced towards the rear of the coach. In general, none of these is harsh or likely to make conversation difficult.
When, with a day temperature of 74° F., the radiator header-tank water reached 190° F. after a fair amount of stop-start traffic driving, I visualized early boiling on the hills, but subsequent steady pulling in the lower gears caused the temperature to drop. I made frequent checks throughout the day and, finding 180195° F. to be the normal temperature,
concluded that the Seddon has an optimum-sized cooling system to obtain maximum efficiency from the fuel. A maximum oil temperature of 150° F. showed adequate air flow around the engine.
As I have previously mentioned, the axle ratio was high and it was not surprising that low-second gear w`as mainly required when climbing Buckstones Road from Oldham towards Delph. Observation of the water temperature showed a drop to 185° F. within a minute of engaging a low ratio with the engine turning at nearly governed speed, and there was only 2-3° F. variation in any of the climbs.
A 1-in-7 incline was just outside the range for starting from rest in high-first gear, but there was plenty of power in hand with the lowest ratio in use.
In its braking, the vehicle tested would satisfy any Ministry of Transport examiner, because the hand brake, in addition to holding the vehicle with full load on sharp hills, gave Tapley readings of 20 per cent. on the level. With modern .hraice:
as friction material it takes probably two to three weeks' hard work to reach full efficiency, and even better results might be expected after a little service.
Likewise, the foot brake, although about average in retardation, can be relied upon for its consistency, as I found after descending one of the longer Pennine gradients, using solely the brakes to check the speed. There was no harshness when the brakes were heavily applied and the Tapley meter registered 65 per cent. against the actual measured stopping distance, 30 ft. from 20 m.p.h. At 30 m.p.h. the coach was stopped in 60 ft.
Using all four gears and low axle ratio, acceleration to 30 m.p.h. took longer than with the higher ratio, when only two gear changes were required. The fastest time recorded in the tests was 28.8 sec., but an average of all the trials from 0-30 m.p.h. in high ratio, using indirect gears, produced a return of 33.9 sec.
Attempts to simulate coach seri/ice were marred by traffic and stops at crossroad. when travelling on a circuit between Oldham and Manchester. Nevertheless, by skilful handling, the works tester completed the course at 28 m.p.h. average speed. The Seddon yielded 18.12 m.p.g., which could probably be improved to over 20 m.p.g. in actual service.
A second test, followed by a repeat run because I could not credit the result, was made with one stop per mile, which was asking a lot, having regard to the high load for bus operation and the axle ratios. Using the gearbox and axle ratios as a " five-speed " unit, the first trial yielded 14.5 m.p.g. and the repeat 14.22 m.p.g., giving an average of 14.36 m.p.g. for inter-urban service. Take a ton from the vehicle, as tested, to represent a lighter bus body without luggage, and the result would be nearer 16 m.p.g.
I was fully satisfied with the performance of the coach as a 16-ft.
6-in.-wheelbase model. There are alternatives, including .a 13-ft. 11-in.wheelbase chassis with Perkins R6,. or P6 engine, but the model tested, will provide interesting competition. with higher-priced luxury models: