Tyres!

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The Concorde flight that had to be aborted during take-off due to tyre trouble — and I am sure the split-second reactions of Captain and crew equal those of racing drivers — makes an excuse to write about tyres. Modern F1 cars usually go through a race without tyre problems, apart from those associated with deciding on the correct rubber-mix for the prevailing weather conditions or pace, unless a puncture is incurred from a foreign body on the road or contact with another car. Other than this, a set of tyres, whether by Avon, Goodyear, Michelin or Pirelli, should last the race, and are only changed as a precaution if a pit-stop for other reasons allows.

It was very different in the old days of the epic road races over stupendous distances. Then covers burst frequently and had to be torn off the rim by hand, aided by a very sharp knife, until the advent of the detachable rim that helped Szisz on the Renault to win the Grand Prix in 1906. Curiously, in view of so much tyre failure—and in the motor-racing book he has just compiled for Pirelli, Leonard Setright reminds us that although Lautenschlager drove cautiously to win the 1908 Grand Prix for Mercedes he still had nine stops for tyres and that some competitors stopped as many as 19 times for fresh covers, which were made of “natural rubber of dubious inconsistent quality, reinforced with zinc oxide which gave them their characteristic whiteness, superimposed on a cotton carcass, and anchored by beads in the edges of wheel rims” — Napier was barred from using detachable wheels in this race. Yet at Brooklands a year before, SF Edge had been aided in his ambition to average more than 60 mph for 24 hours on the then-new Brooklands Motor Course on a Napier, by Dunlop-shod Rudge-Whitworth wheels of this kind, of which 24 needed changing in the 1,581 miles covered.

As speeds increased at Brooklands tyre failure was at the back of most drivers’ minds, even when they were using the excellent Palmer Cords. The short life to be expected from pre-WW1 tyres restricted the duration of record bids and caused Hornsted to execute a record skid in the 200 hp Benz. Admittedly Percy Lambert, lapping at around 105 mph in the 25 hp Talbot to set the World’s hour record at more than 100 mph for the first time, had no trouble with the Palmer lyres; but later he was killed in the same car, due to a burst tyre.

After the Armistice the problem remained. Burst tyres, which all too often would leave the wheels, put Harry Hawker through the Brooklands Railway-straight fencing in the 350 hp Sunbeam, shot Chassagne and his riding mechanic over the Byfleet banking in a Talbot-Darracq during the 1922 JCC 200-Mile Race, killed Dario Resta when the 2-litre GP Sunbeam he was driving also went through the corrugated-iron fence on the Railway-straight, and a boy onlooker had been killed when a beaded-edge tyre left one of the wheels of the 350 hp Sunbeam at Fanoe when Malcolm Campbell was driving it.

This caused Dunlop’s to work fast on the new, safer well-base rim. Ironically, when their 28″ x 4″ straight-sided tyres were used by Ettore Bugatti for the advent of his new Type 35 GP cars at the European Grand Prix at Lyons in 1924, he was plagued by incessant tyre troubles. The astonishing thing is that Bugatti then reverted to Michelin 710 x 90 be tyres, a size scarcely adequate for 40 mph light-cars, judging how quickly Dunlops of this size wear out on my admittedly differential-less 8 hp Talbot-Darracq, yet his type 35s had no tyre failures in the San Sebastian race, which seems to endorse both the make of cover and Ettore’s now-famous aluminium wheels. Bugatti had personally tested these tyres by driving from Strasbourg to Paris at an average speed of nearly 62 mph. Even smaller tyres were used on the racing Salmsons that were called upon to cover 200 miles on the now-rough Brooklands surface —I seem to recall that they were on Engleberts. There was as much competition between tyre companies then as there is today to advertise racing successes and I recall a showroom somewhere behind Great Portland Street, in the windows of which were displayed big photographs of these Salmsons on their bicycle-like tyres.

Tyres, indeed, remained the greatest problem-factor for quite a long time, where the faster, heavier cars were concerned, although even the lightweight Aston-Martin “Razorblade” threw off a beaded-edge tyre whenever it was put to attacking the light-car hour record. When Parry Thomas wanted to take the “Double-Twelve” hour record with the Leyland-Thomas, unsuitable tyres curbed his endeavours. He tried flooding part of Brooklands with water supplied by local fire-engines to cool the highly stressed covers, as Edge did in 1907, and later waited for a wet day, but skidding reduced speed. As late as 1924 he contrived to capture the World’s hour record (at 109.9 mph) by having all four tyres changed quickly at half-distance. And in the course of breaking the 12-hour record that year with the Lanchester 40 single-seater, Thomas suffered 16 tyre changes when lapping at just over 100 mph, and when a Renault 45 took the 24 hour record at 108 mph in 1926 its tyres were changed every hour. Yet, by 1926, Thomas was about to raise the hour record to 121.74 with the heavy Leyland-Thomas, the Dunlops lasting the full distance, although one was in a parlous state at the end.

Much later than that I recall the very many tyre changes required in the BRDC 500-Mile Races. So it was a balance of speed, car-weight and distance run that punished pre-war tyres. Yet if tyres had not improved, courageous George Eyston could scarcely have put the hour record with the big Panhard-Levassor to over 133 mph by 1934.

That it was largely speed that crucified covers was evident from sports-car races. Whereas now, and for some long time, the fastest runners in a race like the Le Mans 24-hour marathon get through without a tyre swop, this was so as far back as 1925. For instance, the twin-cam 3-litre Sunbeam that finished second at the Sarthe that year, as I recounted last month, managed this on one set of Rapsons, although the road surface was terrible and towards the end of the Sunbeam’s run its back tyres were rubbing on the body sides. But the average speed was only 56 mph, and top speed only around 90 mph. Incidentally, Rapson was supplying his special, double-treaded tyres only to the Sunbeam, Talbot and Bentley racing teams at the time. It has been said that, durable and puncture-proof as these special covers may have been, they did not enhance comfort for ordinary driving, which may be why their inventor demonstrated them on well-sprung cars, like the Rolls-Royce and Lanchester . .

Testing as high-speed racing and long-distance record-breaking runs by heavy cars were on pre-war tyres, the ultimate test of them was the Land Speed Record. By 1926 Dunlop’s had the monopoly of tyres for cars built to attempt the ultimate speed and when Parry Thomas was trying for 170 mph in “Babs” (which was rather lower than the speed at which the Concorde’s tyres burst, although the weight difference is far greater!) the aforesaid cotton carcasses were still in use, ten-ply in this case, covered by a thin layer of rubber. Dunlop continued to use ten-ply cotton for all the successful record bids up to 1928 with the Napier-Campbell’s 207 mph — that is to say, including Segrave’s 200 mph record with the twin-engined Sunbeam. After that 12-ply cotton was used, and this sufficed for Segrave’s LSR return in the 231 mph Irving-Napier and Kaye Don’s unhappy try with the Sunbeam “Silver Bullet”.

There was then a move to 14-ply tyres, for the uprated Napier-Campbell, and this remained the norm up to 1935, for the many victorious bids by “Bluebird”, ending with over 300 mph from the Rolls-Royce-powered car. However, twin rear wheels had been employed from 1933 onwards and tyre size had increased from Thomas’ 33″ x 5″ Dunlops to the 35″ x 6″ tyres on the front wheels and the twin 7.00-25 tyres that had been used on “Bluebird’s” Dunlop disc rear wheels from 1933. Then, for fitting to Eyston’s fantastic 7-ton twin R-R-engined monster and Cobb’s twin Napier Lion-powered RaiIton, Dunlop’s introduced 10-ply Fortisan. After the war an improved Fortisan II was used for Cobb’s 400 mph car and on Donald Campbell’s ill-fated Bristol-Proteus “Bluebird”, and a Mk III Fortisan was used for the tyres of the 1963 Donald Campbell “Bluebird”, but still with ten plies.

How the difficulties had multiplied can be estimated when I remark that engine power had increased, even before the war, from Thomas’ problematical 500 hp, to Eyston’s 3,600 bhp., the weight of the tyre/wheel assemblies had risen from the 88 lb of those on the 1928 “Bluebird” to 211 lb for those on Eyston’s monster, and that from having to transmit 13 hp per sq in of contact surface when Segrave unleashed the twin-engined Sunbeam at Daytona in 1927, the tyres fitted to Eyston’s “Thunderbird” put down 46 hp per sq in. In addition, tyre rpm had increased by 1,140 from the days of Parry Thomas to John Cobb assaying the LSR, and the index of centrifugal force which the Dunlop technicians worked to had risen from 89 to 282 in those thirteen years. For the 1963 “Bluebird” the Dunlops were tested to 500 mph and the 7.0-41 disc wheels weighing with the tubeless tyres 270 lb (or 170 lb more than the 200 mph Sunbeam’s wire wheels and tyres) turned at 3,200 rpm at 475 mph. It is also significant that back in 1932 Dunlop’s supplied 14-ply cotton tyres for Wizard Smith’s Stewart Special, which were safe for ten miles at 164 mph. on a New Zealand beach.

The later LSR attempts, culminating in Gary Gabbelich’s 622.407 mph, were run on Goodyear tyres, reputed to have cost some £2m to develop, so when planning Project Thrust for Richard Noble’s attempt on the LSR some time this month a conscious design decision was made early on to run on solid wheels, and the suspension of the car has been designed accordingly. For testing purposes, Thrust was run on ex-RAF Lighting Fighter tyres, made by Dunlop, and rated at 260 mph. The 301/2 inch diameter wheels have been forged by High Duty Alloys and machined by Peter Brotherhood of Peterborough. The rear wheels have a circumferential keel cast into them which will dig into the surface of the Bonneville Salt Flats to give the car some lateral stability, while the front wheels have a pattern etched into the surface. The wheels have been tested up to 8,000 rpm and it is envvisaged that they will reach some 7,500 rpm during the record attempt. The wheels run on Timken taper roller bearings, and one unforeseen problem which occurred in testing was that at the high speeds at which the wheels will be turning, it is impossible to retain conventional bearing grease in the hubs. A firm called Kluber came to the rescue, developing a molecular grease specially for Thrust which will withstand the speeds attained — this has considerably expanded the capability of taper roller bearings, and will have a beneficial spin-off for industry.

Who says record breaking is a waste of time and money? We wish Richard Noble luck in his bid to put the LSR at 650 mph. — WB.

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