Tyres and Steering Geometry ECTUR1NG on "Tyres and Steer ing
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Geometry" before the members of the Institute of Road Transport Engineers on November 27, Mr. J. H. Hardman, of the product performance division of the Dunlop Rubber Co., Ltd., said:
When speeds were low there was no need to develop big forces to keep vehicles on their correct paths, or to worry about over-steering and understeering characteristics, as there was time for mental reaction to function and corrective action to be taken.
Broadly speaking, a vehicle is steered by deflecting one or more of its wheels from the original position. Take a normal vehicle: Deflection of the front wheels misaligns the tyres. These produce a transverse force in the direction of the misalignment which causes the vehicle to travel on a curve. As soon as it is on a set curve, it is obvious that a centrifugal force is set up in a direction opposite and equal to the transverse or cornering force. There is also centrifugal force acting at the rear wheels, and they must be misaligned in the same direction as those at the front, their combined cornering forces equalling the centrifugal force. This means that the vehicle must turn about a point ahead of a line running along the back axle, arid the higher the speed for the same radius, the farther ahead must be this point.
"Slip Angle" and Wear
It is this "slip angle" of the wheels which accounts for increased tyre wear on corners, even if the geometry be correct.
A steel tyre has a fairly large cornering force for a very small slip angle, and this builds up to a reasonable maximum with a small increase in the angle. On the other hand, the cornering force for a pneumatic tyre builds up gradually and progressively to a maximum at about 10 degrees.
It is the possibility of altering this force progressively and easily by turning the steering wheel that gives the driver control, even at high speeds.
The tyre manufacturer tries to obtain as high a cornering power, i.e., cornering force per one degree slip angle, as is consistent with comfort, strength, etc.
It is more important that all tyres on a vehicle have the same characteristics than that the cornering power should be particularly high.
Weight transference from one side to the other, as when cornering, does steer the back axle to a small extent. Some under-steer is desirable. It gives directional stability; carried to extremes, it becomes difficult to deflect the vehicle from a straight path. Over-steering results in the vehicle's making a turn of decreasing radius unless prompt correction be applied to the steering wheel.
An aeroplane with a freely castoring nose wheel is an outstanding example of a stable (under-steered) vehicle; one with a freely castoring tail wheel is the reverse. , A good explanation of the terms " under-steered " and " over-steeri.d " is that an over-steered vehicle is one which makes a ,sharper turn without moving the steering wheel as the centrifugal forces increase; an under-steered vehicle is one which does the reverse. • Little of the life of an ordinary vehicle is spent in making sharp turns, and these never at high speed. Thus quite big departures from the Ackerman principle do not appreciably affect tyre performance. A vehicle with rear-wheel steering is quite unsatisfactory at anything but low, speeds.
Castor angle of itself has no effect on tyre wear; neither has king-pin The author dealt with many other points, but restriction on space prevents our referring to them in detail. PARCEL VANS TO REPLACE MESSENGER BOYS
SMALL traders in Aberdeen cannot obtain messenger boys now that the school-leaving age has been raised, Mr. W. Dixon Connochie told the Appeal Tribunal in Edinburgh on November 28. He appeared on behalf of Mr. George J. Laidlaw Wilson, whose application for a B licence to operate a town parcels-delivery service was rejected by the Scottish Licensing Authority.
In granting the appeal and authorizing a B licence for a parcels-delfvery service within a three-mile radius, Mr. Gleeson E. Robinson, chairman, said that the evidence produced was slight, but the Tribunal thought a prima facie case had been established, Mr. Connochie said that his client applied to Operate a collection and delivery service within Aberdeen for small traders. It was common know ledge that, because of rationing and restrictions, tradesmen had to handle smaller parcels than in normal times. That resulted in an increased traffic in smalls. The evidence, he maintained, proved that the present facilities were not sufficient for the small trader.
Commenting on the reference to messenger boys, the chairman remarked that there was not the same competition between tradesmen as in more prosperous days.
ASSOCIATION HELPS SMALL TYRE MEN
At't T the first general meeting of the
National Association of Tyre Specialists, last week, the presiderit, Mr. A. E. Batt, said that some members had been informed by the S.M.M. and T. several months ago that their premises were inadequate and that their names would be removed from the register of tyre tradeKs.
The national council immediately took action direct and through political channels, with the result that "the heat was taken off."
In many cases no proper inspections had been carried out, and some inspections had been made without knowledge or consent of proprietors. GOVERNMENT ROAD POLICY IS INDUSTRIAL SUICIDE
THE road maintenance committee of the British Road Federation believes that "the Government has failed entirely to realize the implications of its 'present highway policy." The Federation urges the Government to reconsider its decision on capital expenditure in the light of new evidence, which shows that the proposed cuts in labour and maintenance will have disastrous effects on agriculture and industry.
"In view of the warnings given by Ministers of a possible railway transport crisis, the roads will have to bear exceptionally heavy traffic, and the evidence collected by the Federation on the state of the roads shows that expert opinion throughout the country is being ignored," says the committee.
These points, embodied in a resolution passed by the road maintenance committee, were put before the Minister for Economic Affairs and the Minister of Transport in a letter sent to them on Tuesday. ,
A copy of the -letter was issued to " The Commercial Motor" at a Press conference in London on Tuesday evening. With it were extracts from letters from highway authorities covering 14 pages of foolscap. These letters comprise the evidence to which the road maintenance committee referred, and they show that a revision of the Government's policy is urgently necessary in the interests of public safety.
ANOTHER BATCH OF APPEALS
rURTHER appeals to be heard at I Halifax House, Strand, London, W.C.2, from December 16-18, were announced by the Appeal Tribunal on Tuesday. The appeal of Swatton Brothers (Upavon), Ltd., against a decision of the Western Licensing Authority will be heard on December 16, and that of William Feathe.r and Sons, Ltd., against a decision of the North-Western Deputy Licensing Authority on December 17.
The appeals of L. C. Prosser and two
others against decisions of the West Midland Deputy Licensing Authority have been postponed from December 9 to December 18.
TWO-WAY RADIO FLEETS
THIS week, London's first hire cars
with two-way radio communication between driver and booking office were put into operation by Cosycars, Ltd., Streatham. At Montrose, Paton's Taxis have fitted similar equipment to their fleet and claim to have been the first hire service in Scotland to adopt it.
FIFTY YEARS OF BEARINGS
Qo January 11 the Hoffman Manufacturing Co., Ltd., Chelmsford, will celebrate its 50th anniversary. From a small beginning, the company has expanded until it now has branches in 10 centres in the United Kingdom, as well as a large works at Chelmsford.
Many of the employees have served the company for long periods.
IN A LINE OR TWO
As from December 15, the Manchester office and warehouse of Gandy, Ltd., will be located at 4, Wood Street.
A new tyre-service depot has been opened by the Marsham Tyre Co., Ltd., at 51/55, Milton Road, Westcliff-onSea, with Mr. H. E. Cadge as manager.
The haulage and coach business of Mr. John Pritchard has been transferred to John Pritchard (Transport), Ltd., Norway Wharf, Commercial Road. London, E.14.
The Midland Centre of the Institute of Road Transport Engineers is to visit the works of the Birmingham Aluminium Castings Co. (1903), Ltd., at 2 p.m., on December 8.
Vehicle electrical systems and equipmeat will be dealt with by Mr. Bevington, of Joseph Lucas, Ltd., at a meeting of the Industrial Transport Association at the Grand Hotel, Bristol, on December 9, at 7 p.m. -N.R.T.F. COMMITTEE DISCUSSES USERS' PROBLEMS AT a recent meeting of the Vehicles Committee of the National Road Transport Federation, the question of the supply of tyres was specially reviewed. Manufacturers had reported a greatly increased output—in some cases higher than pre-war. The real difficulty lies in the low average life lef in tyres now in use, and to improve the average it is necessary to supply more than would normally be required.
The Committee found that the special procedure agreed with the Tyre Manufacturers' Conference was generally producing tyres to operators in difficulty, but it decided to write to the T.M.C., reporting that the situation was still a
great worry to operators. Reference was also made to the considerable shortage of solid tyres It was also arranged to follow up the question of an increase in the speed limit for heavy motorcars, whilst an approach is being made to the S.M.M.T. in respect of the supply and allocation of new vehicles.
NEW COMPANY TO HANDLE LEYLANDS IN NORWAY
A NEW company, known as A/S
Autoindustri, has been formed by A.S. Strommens Verksted, of Oslo, to handle the agency of Leyland Motors, Ltd., in Norway.
A. S. Strommens Verksted, a pioneer in the construction of light-alloy bodies, is at present building for Oslo Municipality 50 buses. with Leyland 125 b.h.p. oil engines. They will be of chassisless construction, with independent frontwheel suspension and aluminium bodies. Many standard Leyland Tiger chassis have been supplied to Norway.
"PLANNED BUNCHING" CUTS QUEUES
rrplairnonned out n hri unsgh:h ooufr vseuhri eg leess,
—usually avoided by operators—has been introduced by London Transport during peak hours at 10 traffic "black spots" north of the Thames
The improvements in tram and trolleybus timetables, which have cut queues by haff, ard in some cases eliminated them, are the result of close study by operating department experts.
REPORTS ON ENEMY INDUSTRY
REPORTS on German and Japanese N. industry are being published at fairly frequent intervals. The latest include: B.I.O.S. I419—German Autobahn Bridges-15s.; F.LA.T. 1168—The "C" Process of Making Moulds and Cores for Foundry Use—Is. 3d.; C.I.O.S. XXXIII-71—Tyre, Tube and Heavy Plant Manufacture—(Appendix No. 14a to C.I.O.S. Report XXXII-119)--9s.; B.I.O.S. 1494—Developments in Aircraft Construction Using Plastic, Paper. Veneer and Thin Metal in Sandwich and Other Formations-6s.: F.I.A.T. 578-Automotive Power Trains, Clutches, Transmissions and Steering Mechanisms
B.I.O.S. Misc. 43—Information on Manufacture of Oil Seal Rings (Simmer Rings)-6d.; B.I.O.S. Misc. 44—Experimental Diesel Engine at Motorenwerke, Mannheim—ls.