A NEW MARK V MODEL FOR POST-WAR PRODUCTION. INDEPENDENT FRONT SUSPENSION
[We have decided for once to depart from the usual methods in announcing this new car, and the article which follows was written, at our invitation, by Mr. W. A. Rowbotham, of Rolls Royce Ltd. themselves. He tells very modestly how this fine car was evolved and of the many ways in which it improves on the former 4¼-litre.—Ed.]
SINCE Rolls Royce Ltd. took over the Bentley Company the evolution of the Bentley chassis has proceeded on well-defined lines.
The object of the Development Staff has been to produce a completely reliable automobile from which the driver can extract the maximum performance with the minimum amount of fatigue.
There are cars which can put up astonishing averages over certain roads when handled by expert drivers. Performance only interests the Bentley engineers if it can be used by the average driver under average road and weather conditions, seven days in the week. It will not be so used unless the driver is, and feels, safe and also suffers from the minimum amount of fatigue travelling over a given distance. It is not difficult to understand why the above formula fails to produce an exciting car. In point of fact, it can be said that, since its inception, the Rolls Bentley has become less and less exciting to drive at any given speeds. The late 3½ litres were less noisy than their predecessors. The immediate impression was that the car had less performance and therefore was not so thrilling. Ride control improved the high speed stability; a stable car minimises the impression of speed. Big tyres increase the comfort of the suspension; if you are thrown about sufficiently, it is not difficult to believe a fast speedometer, but if you ride smoothly at 90 m.p.h., the impression of speed is diminished.
So the Bentley was evolved, and in spite of its first cost, has always been an economical car to run. To drive as fast as conditions will permit means an average of between 50/55 m.p.h. on most of the English main roads, and yet, even in the hands of a hard driver, it is seldom that the consumption is worse than 17½ miles to the gallon, whilst to require brakes relined at under 50,000 miles is the exception rather than the rule. An enthusiastic owner, Mr. E. R. Hall, one of whose hobbies was motor-racing, was so impressed by the sheer performance of his Bentley, quite apart from its good manners and economy, that he managed to persuade the company to let him run as a private entry in the T.T. over the Ards circuit. To run one single car in any race is tempting providence since a single minor defect or even a puncture may cause defeat. However, having bought the car, it was his to race if he wished. Three years in succession he ran in the T.T., on every occasion against teams of cars having larger engines, and on each occasion he put up the fastest time for the course, though beaten for first place by a small car, on handicap. His average speeds were:—
1934 …. …. …_ 78.4 m.p.h.
1935 (record for any car, supercharged or un-supercharged) . 80.80 m.p.h.
1936 …. …. …_ 80.81 m.p.h.
If anyone has a car which he thinks is fast let him get up early one morning, take it on to the fastest section of the Great North Road, and try to cover 65 miles in one hour. Compare such a stretch with the tortuous Ards circuit, add a tyre change, and Hall’s figures speak for themselves. And so to 1939 and the outbreak of war. At this date a new Bentley, known as the B5, was just starting in production and the first half-dozen had been completed. But instead of gracing the stand at Earls Court, they went into service on war work. They have covered many tens of thousands of miles and now, having become almost veterans, are being lent to the Technical Press, so that the Bentley Public will have something of additional interest to look forward to when Peace comes. The Mark V Bentley, as it is now called, has independent front suspension, a new frame, and more body room, whilst actually being built on a shorter wheelbase. It is an improvement in every respect over its predecessors. It is a little quieter over the speed range, the brakes are slightly more powerful and progressive, the clutch and steering are lighter and the lock is better. The engine is smoother, it pulls better at slow speeds and is less obtrusive when idling. Probably the most noticeable difference between this car and its predecessors is its road-holding, directional stability, and suspension. A description of this sort of improvement can convey little. The narration of an incident during the chassis evolution may be more illuminating :—
Two testers were doing an oil consumption run, comparing the old with the new type Bentley. To get accurate results. one car had to be driven immediately behind the other. The new model was leading. At the conclusion of the run, the driver of the second car walked up to his colleague and said ‘What the dickens were you in such a hurry for? I could hardly keep up with you.’ The reply was. ‘I didn’t drive any harder than usual.’
This is the best description of the new Bentley Mark V. You do not drive any harder, but you put up a much higher average speed without realising it. The Rolls Royce engineers have decided that they must endeavour to produce this sort of result, without sacrificing economy or durability, every time they alter the specification of the Bentley chassis..
The points where we consider that the Mark V has been improved in comparison with its predecessors may be divided up into five sections.
The general silence level of the vehicle has been raised, the engine smoothness has been improved, the ride is better. With regard to the body, access to front and rear seats has been improved, and there is more elbow room and increased luggage accommodation.
The brakes are more powerful; the directional stability of the car has been improved.
The road holding and cornering abilities of the new model are very much better than was achieved on previous Bentleys. This enables a high average speed to be maintained over any stretch of road.
Section 4—Ease of Handling
The starting is now fully automatic, i.e., there is no longer any necessity to adjust the mixture strength. The engine pulls better at low speeds, which means that it is unnecessary to change gear as often as previously. The clutch operation is lighter, the steering is lighter and the lock is better.
At many points durability has been improved by increasing bearing sizes. In particular, the dimensions of the crankshaft have been increased. The rear axle has been modified to give greater ability to withstand abuse. The basic object in redesigning the Bentley has been to enable higher average speeds to be maintained without the driver suffering from increased fatigue. Running through the modifications made to the various units of the chassis compared with the last series, we have the following :—
Independent Front Suspension
Independent suspension is now fitted to the front of the car. This results in three basic advantages:—
Better steering stability at high speeds;
Better cornering ability, and
The suspension also is arranged so that it is completely insulated from the rest of the chassis with rubber. This eliminates the tyre and road noise which is often accentuated by other independently sprung systems.
Crankshaft journal sizes have been increased to improve durability and smoothness. A completely new engine mounting has been evolved, which permits the engine to be driven at full throttle at low speeds, without torque reaction being felt.
A raised crown piston has been standardised, which reduces detonation to the minimum.
A semi-centrifugal clutch is now fitted. This reduces the pedal pressure and gives a smoother take up.
This has been lightened without materially lowering the overall ratio, while the lock has been improved.
This has been enormously increased in stiffness, which, besides increasing the durability of the body, contributes towards the better suspension and roadholding.
This has been completely re-designed to produce simplification and reduce weight.
The opportunity has been taken to strengthen up the rear axle, so that it will stand more abuse than previously.
Owing to the fact that the front suspension parts are more rigid than the conventional front axle and leaf springs, it has been found possible to increase the proportion of front braking without causing the car to deviate from a straight course when a violent stop is made. The Bentley Mark V with standardised body has a top speed which is the same as previous Bentleys, i.e., under favourable road conditions between 95 and 100 m.p.h.
Since, however, immediately prior to the outbreak of war there were a number of Continental roads where a speed in excess of 100 m.p.h. could be utilised, a special model has been developed to cater for these conditions, and this is known as the “Corniche.” The “Corniche” body contributes towards the increase in maximum speed, owing to a scientific reduction in windage, but little room has been sacrificed; in fact, the car is actually wider, though it has slightly less head room. The luggage accommodation is less than the standard car, as the spare wheel is stowed at the back. It is, however, at least 10 m.p.h. faster than the standard model, though obviously, owing to its very high gear ratio and higher compression engine, it is not so tractable in top gear. There is no doubt that the Standard model will prove fast enough for more than 90 per cent. of customers, who habitually use their cars in England. Extensive tests have been carried out on both models on the Continent, and various production models of the Standard Mark V have now covered over a quarter of a million miles in the company’s service. The durability has proved to be better than that of any Bentley which has previously been produced. There is no doubt that the new car will put up a higher average, for the same amount of driving effort, than its predecessors.
[Qualifying the above, the Mark V has independent front suspension using unenclosed coil springs; synchromesh on second gear as well as on the third and top ratios; more conveniently placed gear and brake levers; a new top opening bonnet; and the engine set further forward. Nor did Mr. Rowbotham, in his modest, announcement, mention the comprehensive interior heating system in conjunction with the engine cooling water. The hand ignition control and the radiator shutters have gone.
The over-drive top gear is retained, having a ratio of 3.64 to 1; likewise the famous over-ride suspension control. The wheelbase has been reduced by 2″ to 10′ 4″, the front track is 4′ 8¼” and the rear track 4′ 10″, while smaller tyres, of 6.50″ x16″, are now used. Brakes are now by Girling, tyres by Avon. We publish full test impressions of this historic high performance car on another page in this issue.—Ed.]