The Latest in Tyres
Time was when the ordinary motorist specified only the make and model of his car when ordering tyres. He cared little for their type and his only requirement was that they should be of the correct size. Happily, today’s motorist is much more discerning, particularly the enthusiast, who has virtually accepted the radial-ply, braced-tread tyre as his kind of car footwear. This article is aimed at explaining the latest additions to tyres for the enthusiastic motorist. Well-known tyres such as the Michelin “X,” Pirelli Cinturato and Dunlop SP.41, have been omitted since they are so familiar as to need no explanation. We do not intend this to be a competitive comparison, and the alphabetical list of makers does not necessarily represent an order of merit.
Before going on, a word on radial-ply tyres. These are made with the ply cords running at right angles from bead to bead, whilst cross-ply cords run diagonally. This produces a sidewall which is far more supple than that of a cross-ply tyre, so a device has to be incorporated to stabilise the tread without detracting from the flexibility of the sidewall. Such a means is the tread bracing, or “breaker strip,” of several layers of fabric cords (steel wires in the cases of the Michelin “X,” Avon Radial, and Goodyear G.200) which run around the circumference of the tyre just beneath the tread.
The retention of sidewall flexibility gives rise to a flatter profile when inflated and produces an increased tyre/road surface contact area. In some cases, this also produces a slightly smaller rolling radius and, in the case of cars which are not fitted with radial-ply tyres as original equipment, will result in over-modest speedometer readings.
On no account should radial-ply tyres be fitted at the front unless they are also at the rear. This applies whether the car has front or rear wheel drive, and whether the engine is rear or front mounted. Cross and radial-ply tyres should not be mixed on the same axle, since this produces peculiar handling characteristics and causes the car to behave differently on right and left-hand bends. It is, however, acceptable to have cross-ply tyres on the front wheels and radials at the rear, though for really high-speed driving mixing of any kind is to be avoided. If radial-ply tyres are fitted to f.w.d. cars then they should be on all four wheels. If two textile-braced, radial-ply tyres are used in conjunction with two steel-braced radials, the latter should be fitted at the rear.
Ply rating is a term which has fallen into disuse as far as car tyres are concerned. Rather than an indication of the number of plies it is now an index of tyre strength, identifying the use to which a tyre can be put, and is more appropriately used in the cases of commercials and earthmovers.
A feature on many modern tyres is the large number of rib stabilisers, small rubber protrusions inside the tread openings to prevent complete closure during travel, thus allowing the tread edges to remain capable of squeezing away as much moisture as possible. Closed sipes, or angled knife-cuts, are also present in varying numbers in many tyres. These prevent “chunk out” at speed.
In the notes which follow we have selected two popular sizes, those which fit the B.M.C. Mini and the E-Type Jaguar. Prices are all retail and are those operative at the time of going to press. Prices of tubed tyres do not include the tube, which can be expected to cost about £1. Similarly, prices of tubeless tyres do not include the cost of a valve. Radial tyres have a size structure different from that of cross-ply tyres, and the sizes quoted are correct for that type of tyre.
Avon Radial
The Avon Tyre and Rubber Company, Melksham, Wilts.
This has fabric plies with two layers of steel wire bracing beneath the tread, the wires of one layer being at right angles to that of the other. It is important that it should be fitted with the side-wall lettering facing outwards. It’s dimensions are slightly different of those of other makes and should therefore only be mated on the same axle with another Avon Radial. Production is limited at present, the makers only meeting demands as they occur.
145-10 : Tubed, £5 16s. 0d. Tubeless, £6 13s. 6d. 185-15 : Not yet available in this size.
Dunlop SP.41HR.
Dunlop Rubber Co. Ltd., Fort Dunlop, Erdington, Birmingham, 24.
This is a high-speed version of the popular SP.41 radial-ply tyre, incorporating a textile tread bracing, and is recommended for cars with a top speed in excess of 125 m.p.h. These tyres should always be fitted in complete sets. The size range is limited and no 145-10 size is presently being made.
185-15 : £10 8s. 0d., tubed only.
Dunlop SP.3.
A radial-ply tyre with a tread rather “chunkier” than that of the SP.41. It is available in a limited range of sizes and quantities, though it is expected that this will be extended.
145-10 : Tubed, £5 16s. 0d. Tubeless, £6 13s. 6d.
185-15 ; Not available in this size.
Firestone F.100.
Firestone Tyre and Rubber Co. Ltd., Brentford, Middlesex
A round-shouldered radial-ply tyre with four layers of fabric tread bracing. It is not recommended for sustained speeds over 100 m.p.h., but, under certain conditions of loading and pressure may be taken up to 125 m.p.h. It is available in tubeless form only and in a limited number of sizes, the largest being 205-14 :equivalent to 2.50-14.
145-10 £6 13s. 6d.
Firestone Sports 130. This is a cross-ply tyre which embodies nylon cords and racing compounds. It is recommended for speeds up to 130 m.p.h.
5.20-10 : Tubed, £5 9s. 6d. Tubeless, £6 7s. 0d.
6.40-15 : Tubed, £9 1s. 0d. No tubeless.
Goodyear G.800.
Goodyear Tyre and Rubber Co.(Britain) Ltd., Wolverhampton.
A radial-ply tyre with a fabric bracing belt. It has a profile considerably squatter than the equivalent tyre of a year ago.
145-10 : Tubed, £5 16s. 0d. Tubeless, £6 13s. 6d.
185-15 : Tubed, £8 5s. 6d. Tubeless, £9 3s. 0d.
Goodyear G.200. This has the same tread pattern and the same radial construction as the G.800, but the tread bracing belt is of metallic wire. It is made in a limited number of sizes, the smallest being 155-13.
185-15 : Tubed, £8 1s. 6d. Tubeless, £8 19s. 0d.
India Autoband.
India Tyres Ltd., Inchinnan, Renfrewshire.
A radial-ply tyre with four layers of textile bracing. Recommended for 100 m.p.h. at normal pressures and up to 125 m.p.h. with a 12 lb./sq. in. increase.
145-10 : Tubed, £5 16s. 0d. Tubeless, £6 13s. 6d.
185-15 : Tubed, £9 12s. 6d. No tubeless.
Michelin XAS and XA2.
Michelin Tyre Co. Ltd., Stoke-on-Trent, Staffs.
These are extensions of the familiar Michelin “X,” of which over 60 million have been produced since they first appeared in 1948: Both embody the radial construction and steel tread bracing of the “X,” but with variations. Whilst the “X” is a symmetrical tyre, the “XA” is internally asymmetrical and the “XA2” both internally and tread-wise. Consequently, there is only one correct way to fit them to wheels. the instruction appearing on the sidewall. The reason for this lack of symmetry is given as a realisation that tread edges and tyre sidewall will act differently according to whether they face the inside or outside of the car. These asymmetric tyres are being used on the big Citroens and were in evidence at the recent Motor Shows. They are, as yet, available only in France, and no sizes or prices can be quoted here.
Uniroyal Texsteel
North British Rubber Co. Ltd., 62-64, Horseferry Road, London.
This is a radial-ply tyre with fabric carcass and rayon (not steel, as the name implies) tread bracing. This tyre will not become available until summer, 1966, consequently sizes and prices are not yet available.
Yokahama
Honshu Rubber Co. Ltd. 9 Seymour St. London W1.
These Japanese tyres have only recently made their appearance in Britain, and so far are only being used on long-term test on certain taxis. The extent of tacit range is not yet clear, but many types are said to be on their way very soon, among them both radial and cross-ply varieties. The makers are even prepared to specially manufacture to satisfy a demand. A feature of these tyres is their 50% natural rubber content—a much greater proportion than on most tyres today. As natural rubber does not generate heat as rapidly as synthetic. Yokohama tyres should be less prone to overheating, but their rate of wear may well be higher, though we must wait and see before pronouncing judgement. Tubed and tubeless versions will be available, and we hear that a racing tyre is also being developed.–G.P.