An Investigation into the properties of Pirelli’s Detachable-Tread Tyres
At Oulton Park during a “tyring” test.–The two Morris-Oxford Vs used for an investigation into Pirelli tyres. That on the left of the picture is shod with nylon Extraflex covers, the car on the right has BS3s; in both cases the tyre size is 5.00 x 14 and the pressures used were, respectively, 24/26 and 26/28 lb./sq. in. Note the I.A.M. badge, which was, duty covered over when the “experts” drove!
There is an old proverb which goes, “Give a tyre that won’t stick a bad name,” or words to that effect. Consequently, when a tread-band detached itself from a Pirelli BS3 that was on the back wheel of an Auto-Union 1000 which Motor Sport’s Production Manager was thrashing round the Nurburgring, there was heard gnashing of teeth and wailing in the land. This led to Alfred Woolf, who publicises Pirelli, inviting the P.M., the Editor, and a Pirelli Area Sales Manager to participate in a searching test of these revolutionary new tyres, in order to demonstrate that the tread bands do not normally come unstuck, no matter now high the revolutions achieved by the driver, the wheel, or even the car.
So it came about that one Friday last month the Editor found himself going in the P.M.’s Porsche to Denham to join the test-team. On arrival he was confronted with two almost identical cars which, from a distance, could have been a pair of the latest Peugeots, some sort of Fiat or Lancia. a couple of M.G.s. or Austins or Wolseleys or Rileys, but which turned out to be Morris-Oxfords, one on Pirelli Nylon Extraflex with an unfamiliar tread pattern (used extensively, however, on Fiats), the other BS3-shod. Both cars had full fuel tanks, the depth of their tyre treads had been measured, and the ploy was for the Editor and P.M. to share them alternately on a dash up to Scotland and back, taking in some of the most entertaining roads the Lake District and the Highlands have to offer.
Morris-Oxfords did not seem particularly appropriate to the task in hand, sports cars would certainly have been preferable, but although we have little respect for the body-styling which Farina has sold to so many manufacturers (perhaps because the B.M.C. version is too narrow, its tail fins too obvious) we were soon praising this roomy funnily saloon for its ability to negotiate very heavy traffic to Oxford and beyond at an average speed which would have called for a good sports-car ten years earlier—significant measure of how the performance and controllability of the ordinary cars has improved.
We continued northward, foregoing lunch, on less congested roads to Oulton Park circuit. Here each car put in a number of fast laps, although the one driver who is a member of the I.A.M. refused to go on the circuit, saying he was insufficiently experienced, which probably proves something or other. Of the others, only one of us lapped in under three minutes. but it is significant that each improved his lap times by approx. 5 sec. when using the BS3-shod Oxford. These tyres at first give a feeling of instability, due to their flexible casings, but their superior grip soon becomes evident and corners begin to be taken in impressive drifts. It was particularly noteworthy that whereas the Extraflex screamed loudly as tyres do when tortured in this fashion, the BS3s were uncannily quiet. This silent running is a valuable asset to those who like to hurry round corners and roundabouts without attracting unwelcome attention.
After this Oulton Park interlude all three drivers were firmly convinced of the merit of BS3s over ordinary Pirellis. Every attempt had been made to dislodge the tread-bands but they stayed in place, an ominous tapping noise front the n/s front wheel on one rapid lap proving to be merely a piece of rubber, perhaps eight inches long, which had torn away and was flaying against the wing. Oulton Park is as good a testing ground as it is an excellent circuit, although it was rather surprising to encounter a lady driving her family slowly round in a Zephyr and to have to hoot at some child cyclists, after we had been told the cons:, was clear. . . .
The afternoon was wearing on as the Oxfords pressed off towards Scotland. After some quick motoring over Lakeland back-roads the Border was crossed and late that evening we rolled to a standstill in the congested car park of the vast Peebles Hotel Hydro, where some of the staff obviously do not intend to be overawed by mere visitors.
The self-appointed test-team was off to an early start on the Saturday with an interesting and tyre-punishing route before them, which was to take them across the Firth of Forth on the Queensferry (which will be unnecessary when the new road bridge is completed), up to and round the beautiful and remote loehs of Inverness, crossing Loch Carron in the early evening by the Stromeferry. and ending up at a small but clean hotel in Fort Augustus. Our car had run out of petrol, which merely underlined the hospitality of the natives, the second driver to approach along the lonely moorland road willingly syphoning us a gallon front his Morris into a thermos flask, refusing financial compensation.
Again we had eaten a sandwich lunch while on the move and ended the day ravenously hungry. It is a sad reflection on how Britain neglects her tourist trade that, although hot meals were specified on our schedule sheets, on the two occasions when we arrived at our hotel after 8.30 p.m. they were cold and, on the occasion when we did get to an A.A./R.A.C. recommended house earlier than this, some very active maggots squirmed from the Pirelli rep.’s pheasant as soon as he stuck the cutlery into it….
Sunday saw the cars running south in a howling gale, having crossed Loch Leven by the Ballachulish Ferry. The proposed cross-country journey avoiding Glasgow proved difficult to follow and the Oxfords separated but both crews met again from opposite directions, at precisely the same moment, separated by a just-fallen tree, in Bigger. After refuelling it Was a case of pressing on in torrential rain by a main-road route, although more very interesting motoring of near-rally status was undertaken in making Grassington via the bye-ways of the Yorkshire fells, with some very choice ascents and descents in the region of Wharfdale.
By now we had come to like the ” feel ” of the BS3s which, although they permitted slight wander of the front-end, gripped extremely well on wet roads, even under heavy braking, yet did not delay rear-end breakaway on corners until dangerously late. The steering was a shade heavier when parking but in normal driving there was a distinct reduction in fatigue due to less effort being needed when cornering. Cornering speed was reduced by front tyre scrub when understeering and it was noticeable, particularly on the BS3s, how understeer could be controllably changed to oversteer by lifting off.
On the fourth and last day of the run we were to have been shown how these ingenious Pirelli tyres are made, but heavy traffic in such towns as Keighley, Halifax, Huddersfield and Sheffield made us late at Stoke-on-Trent so, after rapid human refuelling, we pressed on to M.I.R.A. Here both cars were timed round the outer-circuit and immediately afterwards the temperature of the nts tyres was recorded. The Extraflex car lapped at 79 m.p.h., the BS3 car at 80. The respective temperatures were : front, 69″ C.; rear, 70° C. and front, 58″ C.; rear, 55′ C., proving that the BS3s run cooler than Extraflex at speed. On the 75-foot line of ‘the skid-pan, again at almost identical speeds. the 1353-shod Oxford proved far easier to hold on course, although in this ease the temperature situation was reversed, the figures nov being : BS3 front = 82° C., rear = 81° C. Extrallex front = 64’ C., rear = 72 C., clear evidence that the detachable-tread Pirellis had been working more enthusiastically in effectively keeping pace with the driver’s requirements.
All that remained was a fast cruise down M 1, back to our starting place. When fuel consumption was checked the BS3 car was found to have given 30.9 m.p.g., the other car 27.9 m.p.g., corrected for total mileage variation and odometer correction. Wear, measured on the nis front tyres, showed that the 11S3 had lost 1 min, of rubber, the nylon Extraflex 3 mm., equal to a life of approximately 12,000 miles from the BS3 but only 3,000 miles from the Extraflex; for at the start the tread depths had measured 10 mm. and 8. mm., respectively. This must be qualified by emphasising that both cars had been driven unmercifully, the difficult parts Of the route which had been scheduled at 30 m.p.h. being consistently covered at better than 40 m.p.h., while the easier 40 m.p.h. sections were sometimes covered in excess of a 50 m.p.h. average, apart from which much rubber had been sacrificed on the circuits. It is indicative of how identical cars differ that one used 7 pints of Castrol, the other 1 1/2 pints; both were reps’ cars which had each done approx 8,000 miles.
These four crowded days, apart front revealing the foregoing tyre facts, enabled us to assess the modern Farina-styled B.M.C. saloon. The Nuffield Publicity Department has been singularly unable to provide such an opportunity, their excuse being that joarnalists get so excited in these cars that they promptly drive them into solid pieces of scenery, materially reducing the availability of the Press fleet. However, here we were, doing our damnedest in these Morris-Oxfords, which are virtually the same as the Austin A55, Magnette III, Riley 4/68 and Wolseley 15/60. B.M.C. need have no qualms that at last we have come to terms with their product. The Oxfords proved far less flabbily sprung than we had anticipated, the floor gear lever is extremely well placed, and the gear change delightful, the gears and engine notably quiet. The speedometer would go to beyond 60 m.p.h. in third without distressing the rugged engine, the real leather upholstery was appreciated, especially as the Pirelli-made front seat is firm yet comfortable, while although the inner back wheel spins when taking tight corners fiercely the back-axle does not wag the tail of the ox over bad surfaces. The Lockheed brakes proved somewhat heavy but efficient, the cars handled surprisingly well and were obviously improved by BS3 tyres, while details such as the quick-action window winders, tumbler-switch on the facia so placed as to permit headlamps flashing after dark and the accurate clock did not go unnoticed; petrol fumes entered one car, probably from the lockable flap-style filler cap, and the 1/4-lights badly need rain gutters. Safety factors include childproof door locks and door handles that have to be pushed up to open the doors, while the cubby-hole is supplemented by a full-width under-facia shelf and the boot is of very liberal dimensions. The overall opinion of the quartette was that B.M.C. have a very good family saloon in these Italian-styled 1 1/2 litres. —W.B.