Development Work on an Individualistic British Car with Twin O.H.C. Six-Cylinder Engine and Independent Rear Suspension.
The Lagonda is a make of car which has always been held in high esteem by enthusiasts. After an early venture in the light-car field, with the 11.1 and 11.9-h.p. models which are now collector’s pieces in vintage circles, came the clever, complicated 2-litre, followed by the “16/80” and 3-litre Models and then the classic 4½-litre. Shortly before the war Lagonda, Ltd., still in the works by Staines Bridge nowadays occupied by Petters, Ltd., called in the services of W. O. Bentley and the 4½-litre was endowed with i.f.s. and the V12 made its debut, a dignified fast car which needed frequent use of the lower gears to get the best from it.
During the war “W.O.” began work on the present 2½-litre “six,” having as his objective a really high-performance car of compact engine size, and providing a ride of exceptional comfort for all occupants. Just before the old company got into difficulties and sold out to David Brown, Ltd., I was able to persuade W. O. Bentley to submit to an interview, quite a scoop in itself, and productive of some exceedingly interesting information about this outstanding new Lagonda. Unfortunately, David Brown had to somewhat modify the design during the subsequent two years, before the car went into production, and as they had just taken over when I was ready to publish the story, it was deemed inadvisable to withhold it. Last month I went to Feltham, where David Brown make the Lagonda bodywork and assemble the 2½-litre from engine, gearbox and chassis components made at Huddersfield, to talk to John Stirling about the development work of the past two years.
Mr. Stirling was emphatic that “W.O.’s” excellent design has not had to be changed to any appreciable extent. The items that have been altered were mainly modified to facilitate production—and today twenty Lagondas come out of Feltham every month.
The chassis frame as originally designed was magnificently rigid torsionally, but lacked local stiffness to the extent of discarding shock-absorber brackets and similar subsidiary attachments. The same “X” frame was retained, but its girders are now boxed-in to secure complete rigidity. Incidentally, no drilling of the frame members is permissible when special bodies are being fitted, as this might destroy the strength of the new exceedingly strong structure. This very wonderful example of modern chassis is made for David Brown by Rubery Owen. Another modification was that of increasing the front track by 2 in., in order to get the front brake drums out into the airstream, cool brakes being a vital feature of a 90-m.p.h. car.
The engine was practically unchanged, except for a new distributor, devised jointly by Lagonda and Lucas, which materially improved bottom-end acceleration, and eliminated the former rather chronic pinking. The total weight of the saloon model was also reduced from rather more than 31 cwt. to approximately 29 cwt., the 0-50-m.p.h. acceleration figure being unproved by nearly three seconds in consequence.
W. O. Bentley had installed the delightful Cotal gearbox, ingeniously reducing its length, and thereby its weight, by using it separate reverse-gear box on the final-drive unit, selected by a pull-out dash-board control. At one time David Brown contemplated manufacturing Cotal gearboxes, but the project was dropped when it was found that a less expensive, lighter and closer-ratio box of normal synchromesh pattern could be manufactured.
This is controlled by a steering-column lever, and obviously eliminates the rather tricky remote-control necessitated for the aforementioned separate reverse-box. The David Brown box weighs 83 lb., a saving of approximately 40 lb. over the Cotal box and separate reverse-unit. Its ratios are 1.1, 1.33, 1.98 and 2.92-to-1, as against the Cotal ratios of 1.1, 1.385, 2.143 and 2.968-to-1.
When David Brown took over the Lagonda Company they acquired two complete prototype cars fairly near to the proposed specification for the production model. These were subjected to extensive testing on the Continent, on three occasions by drivers independent of the company. As a result, further small modifications were made, notably to the rubber bushes at various moving parts about the car. But, fundamentally, the design of “W.O.’s” masterpiece is unchanged, as details in the accompanying panel indicate.
One of the Lagonda’s most outstanding features is its suspension—independent at the front by specially-shaped wish-bone links and coil springs, at the rear independent also, by triangular links and torsion bars, as a compromise between the swing axle and the parallel-lever systems. The front suspension unit ensures a virtually constant steering castor-angle as the front wheels-rise and fall. Unsprung weight is very low and the wheels pivot on two balls in sockets on the ends of the wishbone links. These pivots are lubricated automatically from little half-pint reservoirs, from which oil reaches them by gravity as a ball-valve is motivated by movements of the chassis—clever and effective. For the benefit of the technically-minded, the coil springs have a wire diameter of 0.58 in., the mean diameter of the coils is 4.5 in., the number of effective coils 9½, the normal load 1,225 lb., the deflection to normal position 6½ lb., the bump-load 1,050 lb., the total deflection to bump 8.9 in., deflection normal to bump 2.4 in., the spring-rate 189 lb., the stress at full bump 99,000 lb./sq. in., ditto, corrected, 117,000 lb./sq. in., the stress at normal position 72,000 lb./sq. in. and ditto, corrected, 85,000 lb./sq. in.
The layout of the independent rear suspension deserves careful study. The tubular arms locating the axle stubs pivot on the frame in ball joints in rubber mountings. The wheels tilt only slightly as they rise and fall. The torsion bars run parallel with the frame side-members and are carried on rubber bearings. The torsion-bars are 54 in. long, of which the effective length is 49½ in. The length of the serrated portions is 2.025 in., the diameter 0.8995 in., and the rate is 250 lb. in./degree, the mean stress 122,380 lb./sq. in., the normal stress 81,700 lb./sq. in., the angle of deflection from free to maximum rise is 68 deg., the angle of deflection, free to normal, 45 deg., and the angle of deflection, normal to maximum rise, 23 deg. The torsion bars have a permanent “set” of 15 deg. Note that, in the modern manner, the front suspension is softer than that at the rear. Incidentally, the sound deadening effect of the bonded rubber mounting for the bevel-box, etc., as devised by W. O. Bentley, is, I am told, completely effective and has not been altered.
Whether, in this chauffeur-less age, independent suspension at the back of the car is worth the complication and expense is an intriguing subject for debate. Perhaps for the tender-hearted, who wish to ensure a ride for their offspring, nannies and in-laws as comfortable as that they themselves enjoy, it is. And I believe the rear-seat ride of the 2½-litre Lagonda is a new experience in motoring—I have never been able to find out for myself, because the only demonstrator has always been out demonstrating in the hands of a Lagonda distributor or has been away on further testing whenever I have been at Feltham. Comfort apart, it may be said that i.r.s. provides improved braking and lack of wheelspin under acceleration, but it remains a fact that it has not been deemed necessary to employ it for the faster Aston-Martin. Possibly a de Dion back axle is the ultimate in modern rear suspension, and it may be whispered that such a layout has been tried out by David Brown, Ltd., on an Aston-Martin chassis. Further tests are pending to see what will be the effect of top-hamper represented by closed bodywork.
Reverting to Lagonda, the weight distribution of one of the first coupé 2½-litres, with full petrol tank, was 15.2 cwt. on the front wheels, 17.3 cwt. on the rear, and this remains about the same for the present, lighter cars.
I recall raising with “W.O.” the matter of his preference for bolt-on, as distinct from centre-lock, wire wheels, He advanced the usual arguments of lower cost and weight and I was interested to learn front Mr. Stirling that the pendulum lets now swung this way to such in extent that some clients object to wire wheels on the Aston-Martin, presumably finding discs easier on the eye and the chamois leather.
The reborn Lagonda should have a big future—in this country, in America particularly, and elsewhere. It is inexpensive as cars of real quality go and it has distinct character and individuality in an age of increasing standardisation. The engine is designed to remain happy without serious attention for at least 50,000 miles and it is likely to run 100,000 miles without general overhaul in the hands of private owners. To facilitate body-building a new saw-mill has been put in at Feltham, and as the old Aston-Martin shops were inadequate for chassis manufacture, this aspect of production is looked after in the North.
The car has been adapted for commercial production and its present sponsor, David Brown, who frequently flies down from Huddersfield to Feltham in his Beechcraft, is so enthusiastic and such an idealist that he has sometimes to be reminded that Lagonda, Ltd. exist to make motor cars seriously and not as one-off models for enthusiasts! With so keen a managing director, this long-established make is assured of being kept well abreast of the times. The 2½-litre engine will be raced this year in Aston-Martin aerodynamic coupés at Le Mans and elsewhere. It will be recalled that last year one of these Lagonda engines did extremely well in this capacity at Le Mans until its plumbing arrangements let it down. Feltham may be said to be facing the future with confidence.—W. B.
Specification of the 2½-Litre Lagonda
Engine: Six cylinders, 78 by 90 mm., 2,580 c.c. Inclined o.h.v., operated by two o.h. camshafts. Compression-ratio 6.5-to-1. Two horizontal S.U. carburetters. Coil ignition. Pump and fan cooling. Sump capacity, two gallons. Autoklean full-flow oil filter. 105 b.h.p. at 5,000 r.p.m.
Gearbox: David Brown synchro-mesh, with column shift. Ratios: 4.56, 6.20, 9.15 and 13.6-to-1.
Transmission: Open shaft to hypoid bevel final drive on chassis frame.
Suspension: Coil-spring i.f.s. Swing axle, torsion-bar i.r.s. Armstrong shock-absorbers.
Tyres: 6.00-16 on bolt-on disc wheels.
Brakes: Lockheed hydraulic.
Chassis details: Rack-and-pinion steering. Wheelbase, 9 ft. 5½ in. Track: front, 4 ft. 8 3/8 in.; rear, 4 ft. 8¾ in. Ground clearance, 7 in. Tank capacity, 19 gallons. Dry weight: 31 cwt.
Prices (basic): Saloon, £1,750; coupé, £1,798.
Makers: David Brown, Ltd., Feltham, Middlesex.