CHAIN CHATTER, August 1950

CHAIN CHATTER

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subject under discussion is steering and roadholding rather than how to get, more power from the engine. One of the major items discussed is “forks,” front and rear. For normal motorcycling telescopic forks have been accepted almost without question, although Vincents were not convinced and in consequence evolved their excellent Girdraulics. The racing world, however, was not satisfied to accept telescopic forks as the ultimate answer to front-end stability and even now there is a wide divergency of opinion on the matter. B.M.W. utilised the telescopic fork many years before the war and still adhere to it, as do Nortons and the ” Porcupine ” twin A.J.S.s, but Veloeette and Gilera are not convinced that the telescopic fork is ideal for ultra-high speeds and continues to fit girder forks working on the parallelogram layout, with a central undamped coil spring. The new 51.V.s which appeared for the first time at the Belgian G.P. also fit girder-pattern forks, using diminutive torsion bars as the springing medium. Guzzis felt that neither of the aforementioned forms of fork were ideal and developed the bottom-link layout that has since been adopted by Douglas and which, in basic principle, is akin to the early Castle and Harley forks used by “trough-Superior. While the Guzzi fork has many faults, its good points make it by far the most efficient form of mounting for the front wheel. A study of 0172i, Gilera, Norton and Triumph front wheels over a very fast. section of the Barcelona circuit revealed without question that the bottom-link fork was the most efficient as far as keeping the wheel in contact with the road was concerned, though, of course, this is not all that a front suspension has to do. Purely coincidental, but nevertheless exceedingly interesting, is the fact that

all the machines that ‘finished first in the two recent classics, where England and Italy clashed officially, namely the Belgian and Dutch Growls Prix, were using girder forks with single central eoil-spring—-Velocette in the 350 c.c. doss, Mondial in the 125 c.e. and Gilera Four in the 500 c.c. class, while Eric Oliver still insists on girder-forks on his Norton for winningsidecar events. One cannot take this to mean that girder forks are the best for all classes of road racing, for telescopic forks should have won the Belgian G.P. ;. it was only a faulty rear tyre which stopped Geoff Duke bringing his Norton “Mute first. This sweep by girder forks does, however, indicate that successful racing motorcycles can still get along with the ‘ oldfashioned ‘ type. The Client concern has even gone so far as to state in print that they consider the girder fork essential for good-steering at the speeds their four-cylinder models attain. • At the rear end of the motor-cycle most people are in agreement that the swinging. arm principle is the one to follow, although it was not until this year that Nortons got into line with the rest of the racing world. While the fundamental layout of all the machines is the same the Spring medium and the method Of mounting has Many variations. Norton, A.J.S., Velocette and many privatelybuilt one-off machines use Self-contained telescopic springing units, on each side of the rear wheel, mounted at Varying angles to choice, but in principle working in a vertical plane. The: spring medium used inside the units varies between air and coil-springs, oil damped in one or both directions, and it is on this subject of damping that so many people ore concentrating at the present time. General agreement rates the A.J.S. springing unit one of the most, efficient, while there are many small-productionunits made by various enthusiastic amateurs that receive full marks. The Italian designers have very, different ideas on controlling the movement of the rear swinging arms, Gutzi believing that only one spring unit. is necessary, this being a coil spring in compression unmated horizontally beneath the engine unit and operated by a link -median isin behind the gearbox. Gileras Also believe in horizontal coil springs, but theirs are • Mounted one on each side of the rear wheel parallel wit It the swinging arms and compressed by a similar linkage arrangement to t hat used by Guzzis. Last year Client used a short transverse torsion bar on the four, cylinder bicycles, but this year they have reverted to the coil spring. The new M.V.’ however, has taken up the torsion bar for the rear-swinging arms, but at the moment it is not under control, as anyone who watched Arteskini riding at the Belgian G.P. will have observed. At present this ” trailing link ” method of attaching the rear wheel to t he rest of the, motor-cycle is favourite. but whether it will be superseded in the same way as it has in the automobile world is not known, but there is no reason to suppose that a new form of movement will not be designed eventually:

The recent unfortunate affair at Francorchamps on the second lap, which involved the ” works ” Norton and A.J.S. riders, has brought. home to many people the fact. that a ” works ” rider is no ordinary mortal. When you have in the 500 c.c. class three Nortons, three A.J.S.s, three Gilera Fouts, one MN. and two Velocettes all ridden by firstrate men all eager to get the lead, the racing on the opening laps is obviously going to be very close and the riding on .the cornets has to be of the very highest order. Competition in the 500 co. class is becoming so keen that One views the future with Some apprehension, for next year one can foresee full teams of M.V.s, B.M.W.s and Malls joining in the fray, as well as the new four-cylinder Guzzis. One can discuss the whys and -wherefors Of this difficult situation for ever and still not find a solution ; the fact remains that racing is inherently a dangerous sport and can never be otherwise, but one can diminish the danger factor by ensuring that “works ” nunthines are handled by “works quality ” riders in the bigger events.

So often one hears a well-meaning enthusiast, even riders sometimes, saying “if only I had Duke’s motor-cycle I could go as fast.” Maybe so, in a straight lineand ‘alone, but it is the etirners which count and the first few laps of a Grand Prix that tax a rider’s skill to the limit, while, in addition, four or five riders may engage in a wheel-to-wheel battle for a Whole ram. Unfortunately, due to tradition-ridden belief in the Isle of Man TT., the English enthusiast has never had the opportunity to witness a massstart Classic. If there was a Grand Prix circuit in England where full teams of “works” machines mad do battle with no holds barred, and from a standing start, then we should get a lot less of thiS “me too” attitude, and is top-line ” works ” rider would receive more praise than at present and hats Would be universally doffed to a race of very talented men.