Some notes compiled after a visit to the Avon India Rubber Co., Ltd., at Melksham
IN recent years some important racing successes have been achieved by the Aston Martin team-cars running on Avon racing tyres, and Avon tyres can be said to be in almost universal acclaim amongst the leading exponents of the art of motor-cycle racing.
To the Avon Company there is nothing new in such success in the field of motor racing. As long ago as 1920 the name Avon was respected at Brooklands and many of Kaye Don’s victories with cars such as A.C. and Deemster light cars, the aero-engined Wolseley Viper and the G.P. Sunbeam were achieved with this make of tyre, while, in 1928, the first Ulster T.T. Sports Car Race was won, by Don, at the wheel of an Avon-shod supercharged “Hyper” Lea-Francis. However, by 1932 the business of making car and motorcycle tyres occupied the whole attention of Avon and racing activities were abandoned.
After the war A. F. Walsham, then representing a well-known chain manufacturer in competition circles, was approached by George Brown for advice about tyres for his Vincent-H.R.D. in sprints and Avon were persuaded to make covers for this purpose. This led to the Vincent Company going to Avon for tyres with which to attack World’s motor-cycle speed records. Then Norton, in trouble with racing tyres and losing races, turned to Avon. Avon-shod Nortons ran in the Ulster G.P. in the summer of 1952 and for the Monza race that year T. J. P. Joy, head of the Avon Technical Department, loaded his Jowett Javelin full of racing tyres and drove down to Italy to observe the Nortons in action. By then Walsham had joined Avon as Competition Manager. When Geoff Duke decided to try his hand at sports-car racing with an Aston Martin he exposed a distinct preference for Avon tyres. This led the Aston Martin team to use Avon racing tyres exclusively from 1953. In that season they gained successes at Sebring, in the Mille Miglia, at Silverstone and Charterhall and won the B.E. Trophy Race, the Goodwood Nine-Hour Race and the T.T.
Avon were well-equipped to supply racing tyres for the team Aston Martins, because as soon as possible after the end of the war they had foreseen the need for a scientific approach to tyre testing and had installed at Melksham an unique tyre-testing machine, which, in 1950, was still the only one of its kind in Europe.
This machine is still in use and tests all types of tyres under conditions which simulate road use—the variables being king-pin inclination, steering and camber angles, under different speed and load conditions. This machine, its drum electrically-rotated, is still in use and tests tyres to speeds of up to 120 m.p.h. Another machine has recently been installed, additional to the batteries of routine duration-testing machines, which can run to the equivalent of 210 m.p.h.
The present almost universal use of Avon tyres in motor-cycle racing stemmed from the time when Duke went to Gilera and insisted that Avon went with him. The rest of the Gilera team found increased confidence after trying the Melksham-made tyres and soon all works Gileras were so fitted. After a memorable wet T.T. in the I.O.M., when Avon tyres showed marked superiority, Moto-Guzzi became interested, the late Fergus Anderson demanding Avons for the Belgian G.P., and the 500-c.c. Guzzis going onto Avon for the German G.P. that year. Mondial followed suit from last year and this year Avon can chalk up successes by almost every make of Continental machine.
The car racing tyre, when Aston Martin turned to Avon, was evolved from knowledge gained with motor-cycle racing tyres, but considerable development work was necessary. Indeed, this never ceases, because as tyres improve, so racing cars go faster, constituting the well-known and seemingly inevitable vicious circle.
During our visit to Avon we discussed the subject with D. M. Turner, M.A., the Tyre Development Manager, and D. C. Hartley, M.A., in charge of Car and Motor Cycle Tyre Development. They both emphasised that, although each new stage in racing tyre evolution is first proved on the test rig, there is nothing to beat testing on circuits and in races, and in particular, the opinions of racing drivers, especially the leading drivers with whom Avon are fortunate to be in contact, are of the greatest possible value. In this respect, Surtees and Duke are exceedingly helpful in the motorcycle field and Roy Parnell and Salvadori have assisted with special tests of car racing tyres. “Bob” Walsham is closely in touch with the requirements of the racing teams, Avon’s cheerful Competition Manager not being adverse on one notable occasion, when Sidecar Champion Oliver lacked his usual passenger and was impatient to practise, to donning leathers and occupying the “chair” himself.
There are two other important factors contributing materially to Avon’s success in racing. One is the presence of both Mr. Turner and Mr. Hartley at the leading car and motor-cycle fixtures, so that these technicians see the problems involved and study conditions at first hand. The other factor is that, so far as car racing is concerned, Avon have only Aston Martin to cater for and consequently they can give this team wholehearted support in respect of supplies and fitting-service at the circuits without incurring a too astronomical expenditure over this aspect of tyre research. The only occasion when they departed from this policy was to supply at short notice some Avon tyres for the Formula 1 Connaught.
In racing tyre design such factors as the rubber compound, weight, contours and tread-pattern are of vital importance. After 1955 the speed of the sports-racing Aston Martins rose appreciably, setting fresh problems. These Avon met in three stages—changing to a new zig-zag tread pattern, following, last year, the policy they had introduced in 1955/6 for motor-cycle racing tyres, of using nylon cords, thereby reducing temperatures, enabling a thinner, lighter tyre to be used, and, from 1955, using a new tread compound, which replaced a compound formerly based on that of the normal car tyre, this change producing the greatest benefit of all in respect of improved lap-times, which were reduced by some 3 sec. in the wet and 2 sec. in the dry at Silverstone.
The ideal is a rubber compound soft enough to ensure good roadholding yet sufficiently hard to achieve the required life by resisting abrasion. Generally two types of racing tyre are desirable, one for short races, another with the ability to last as long as possible, at the expense of less satisfactory road holding.
In recent years the phenomena of wave or ripple in the treads of high-speed tyres has been the subject of considerable investigation. This ripple causes a rise in temperature which results in loss of the tyre tread. By experimenting on a testing-rig to discover under what conditions of speed and load severe ripple sets in it is possible to ensure that the critical temperature will not be reached under racing conditions. This is further guarded against by taking tread temperatures during practise before a race, but in this connection tyre technicians are sometimes faced with a driver of the calibre of Moss who will go faster in the race than he has during practise. It is significant that as long ago as 1954 Mr. Turner of Avons, delivered a paper on this subject of ripple in high speed tyres.
Different circuits naturally have varying effects on tyre wear. Goodwood, with its anti-skid surface, is a notorious tyre scruffer, whereas Le Mans nearly approaches the ideal. The Nürburgring is severe, Spa far lighter on tyres. During the development of tyres for Aston Martin Avon discovered that the stiffness of a front antiroll bar could have an unexpected effect on tyre life. Thus at Goodwood, the car with the less stiff anti-roll bar handled better and thus was faster and wore out its near-side rear tyre faster than the same car with a stiffer anti-roll bar but it also showed less wear on the near-side front tyre than the slower car, presumably because greater roll distributed the load more evenly between the front tyres.
On most circuits the order of greatest wear is, first the near-side rear tyre, followed by off-side rear, near-side front and off-side front tyres. As early as 1953 Avon had found that with the Aston Martins, assuming the near-side rear tyre to be 100% worn, the near-side front tyre would be 70% worn at Sebring, 91% in the Mille Miglia, 64% at Le Mans, 92% at Goodwood and 46% at Dundrod. Comparative figures for the off-side front tyre were 78%, 91%, 64%, 56% and 36% and for the off-side rear tyre 96%, 110%, 88%, 76% and 100%. Thus they knew that at the Le Mans and Dundrod the front tyres should last twice as long as the rear tyres, provided the latter were changed just before the rear-side rear tyre had become 100% worn. Conversely, Sebring and Goodwood called for a change of all wheels each time but in the Mille Miglia of those days the Aston Martins didn’t require a wheel change.
Early in 1955 Mr. Hartley and Mr. Turner delivered a paper in Birmingham on Racing Tyre Design before the Midland Section of the Rubber Industry. In this they dealt with handling characteristics, tread wear, power consumption, wave formation and carcass design. The authors emphasised that there is no substitute for track testing of tread compounds and said that the comments of an expert racing driver are very valuable. Under racing conditions the greater the loading of furnace black, within limits, the better the resistance to abrasion but the lower the resilience, so that heat generation becomes greater. It was pointed out that 7% power/weight ratio increase in a racing car can increase lap speed at Le Mans by 1%, so that, if the power consumption of each tyre on a car developing 200 b.h.p. is reduced by about 5% at 120 m.p.h., in a 24-hour race seven miles would be gained, or more than twice the margin by which the Le Mans race of 1954 was won. Tyres of nearly semi-circular cross-section resist centrifugal stresses and offer high circumferential tension. Actually, the section has to be more than semi-circular as there must be a component of the tension in the carcass acting on the beads to keep them against the rim flanges. To give great strength yet keep weight down nylon or terylene is attractive and apparently was used exclusively for Indianapolis tyres from 1954. There are substantial reasons for racing tyres having tread patterns consisting of solid studs or prominent ribs. On making contact with the ground, if the tread elements are independent they are initially undistorted and the distance taken for sheer strain to build up to its critical value is a little longer than usual. If in addition, there are various-sized elements in the pattern, there will be some spread in this “build-up” distance, which in turn should induce a gradual breakaway as the slip angle increases.
From these and subsequent findings the present Avon racing tyre has evolved. This has a casing composed of six plies of nylon cord, and is of a squat shape, the cords crossing over the crown at an angle of 25-30 deg. to the circumference. The tread pattern consists of a beefed based rib with interconnected triangular studs, the tread contour being almost flat to place the maximum area of rubber on the road surface. This design of racing tyre has already given the Aston Martin team wins in the British Empire Trophy Race at OuIton Park and in the 1,000 km. Sports Car Race at Nürburg. Readers may recall the picture MOTOR SPORT published in July, showing how the Moss/Brabham Aston Martin won the latter race because only the rear tyres required changing at a time when Hawthorn’s Ferrari required four new wheels. It is interesting that whereas in 1957 Aston Martin won this race with only one change of rear wheels, this year all four wheels of the DBR1/300 had been changed during a previous pit-stop, evidence of how tyre wear is accelerated by a comparatively small increase (1.87 m.p.h.) in race speed.
From these tyres Avon developed the Turbospeed tyre for high-speed road driving. The racing tyre was the starting point but in the Turbospeed a greater weight of tread is permissible to improve mileage and for quieter running and grip on a wider variety of surfaces than are met on race circuits a well-slotted continuous rib tread pattern was evolved which preserves the basic pattern and flat tread contour of the Avon racing tyre (see illustration). When the tyre is under load, the ribs touch and support each other at intervals, so improving the stability of the tread and damping out excessive squeal noise. The length of the features in the tread pattern is varied round the circumference of the tyre in accordance with the principles of frequency modulation in order to break up into a less recognisable noise any single whine note due to the regular impact of the pattern.
The tread rubber is the same compound as that developed for the racing tyres. The casing is composed of high-strength cords which have excellent low-growth properties and high resistance to fatigue. Due to the need for a compromise between comfort and high performance the cord crown angle is slightly higher at 32-35 deg., i.e., halfway between racing tyres and normal road tyres. Success in racing leads to benefits in production components, and the Avon Turbospeed tyre, with its racing ancestry, is a valuable contribution to better roadholding and greater safety in high-performance cars.
Motor-cycle tyres are the primary concern of the expanding Avon factory at Melksham and consequently their splendid near-monopoly of motor-cycle racing means much to them. On the car side, however, Aston Martin undoubtedly benefit from having a monopoly of Avon racing tyres, and we find production Aston Martin, Peerless, Rover, Vauxhall and other cars supplied with the appropriate Avon tyres as standard equipment.
The Avon technicians, competitions staff and workers are one happy family and in this much of the Company’s strength lies. A test fleet is maintained which includes Ford, Vauxhall (this make is used by Waltham for his long-distance Continental duty-tours) and 3.-litre Jaguar. Mr. Turner uses a Ford but has an Austin-Healey Sprite on order.
Avon-equipped Aston Martins will compete in this year’s T.T. This looks like being a hard-fought race, particularly gruelling on tyres, and it will be interesting to see whether this year’s T.T. on September 13th at Goodwood will be won on Avon, as was the first Ulster T.T race thirty years ago.—W. B.
Land’s End to John o’Groats at nearly 50 m.p.g.
On August 5th/6th a privately-owned Goggomobil coupé 300, driven by T. Gosnell and J. Fry, completed the journey from Land’s End to John o’Groats in 22 hr. 43 min. The distance of 8731 miles was thus covered at an average speed of 38.43 m.p.h.; petrol consumption was 49.17 m.p.g. The Goggomobil weighed over 14 cwt. with passengers and luggage, some 1 1/4 cwt. over the maximum “permissible weight” laid down by the makers. Esso petrol and two-stroke oil were used, and the car was originally supplied and regularly serviced by Connaught Engineering, of Send, Surrey.