OPINIONS FROM OTHERS.
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Editor invites corresponlence on all subjects ;onnected With the use of commercial motors. Letters should be on one of tae paper only and typewritten by preference. The right of abbreviation is reserved, and no responsibility for rzews expressed as accepted.
The side
Damage to Roads.
The Editor, THE COMMERCIAL MOTOR.
[1671] Sir,—Your correspondent "Engineer " is partly answered by the Kent surveyor, Mr. Chapman, in your same number on page 515.
The reason why weakly-constructed roads corrugate or wave under modern high-speed traffic is well known. Naturally, some' of the road engineers wish to throw as much blame on the vehicles as poSsible in order that the vehicle owners may contribute more than they do at present towards the cost of the roads -hence the very varied and interesting opinions put forward in the evidence given before the Local Clovernme ent Board Departmental Committee—but they are beginning to admit the truth that the chief and principal cause is the poor methods of construction of waterbound roads which followed on the introduction of steam rolling. If road stone of very good quality is spread without due care, then covered with small material or road scraping, ealled "hogging" or "blinding," deluged with water, and then rolled to a level surface, the stones are forced apart by the roller and the spaces between them are filled with "hogging," whith afterwards washes out, leaving the stones free to move and respace themselves so as to form waves, the stones being pressed close together at the Oummits and apart at thepoints midway between these wave summits. A really good. roller driver knows how to minimize this and to roll so that the stones knit together and mutually support one another. When this is done, and the surface made waterproof, the crust so formed only needs the protection of the carpet recommended by Mr. Chapman to last for long periods without noticeable corrugation. All vehicles tend to produce waves in the surfaces the wheels pass over ; even on railways and tramways short corrugations are often found. But corrugation in roads can always be kept down by making the road crust fairly strong and rigid, and protecting it by a carpet of elastic bituminous material. Of course, the breaking up of road surfaces for pipe-laying, surface boxes, and similar interruptions to regularity of surface tend to produce waves, and these should no longer be allowed to exist.—Yours faithfully,
ANOTHER ENGINEER.
• Are Radius Rods Necessary ?
The Editor, THE COMMERCIAL MOTOR.
[1672] Sir,—Some interesting and conflicting expresSions of opinion on this question have recently appeared in the columns of THE COMMERCIAL MOTOR. The real question is : can one mechanism successfully perform the functions of suspension, torque and thrust member ? An unqualified affirmative is given by the behaviour in the drastic test of war service of countless lorries employing the three-in-one mechanism. The names of Da-tinier, Thornycroft and A.E.C. occur to one as examples, and in justice to these and other makers the opinions of "Spring Drive ".(" CA.," November 21st) and " Hephaestus " (" CM.," December 5th) cannot go unchallenged.
It has not been found in this test of war service (surely the severest reliability and efficiency test thatcould be imagined) that the lorries embodying the three-in-one system are more prone to the failures scheduled by Spring Drive" than are others with separate suspension, torque and thrust members. Neither is the suspension of the one type noticeably inferior to that of the other. Indeed, it would be hard to detect any difference in actual use under similar conditions. Who could say, for example, that C44
a "J-" type Thorrrycroft is less comfertable to ride in than alteavy subsidy type .Leyland? The writerhas made long journeys inacie and on the driver's seat of both these lorries, and could not say that one rides better than the other.
The opponents of the three-in-one system must be reminded that failures of torque tubes, torque gird,ers, thrust rods; their bearings, brackets and attachments are by no means unknown. An experienced repairer can vouch for the fact that the several' bearings of those parts rarely, if ever, receive constant adequate lubrication. The three-in-one system is so much easier for the driver and maintenance man.
If some -Makers who employ the combined suspension, torque and thrust member would endeavour to improve the means of securing the spring to the axle casing we should find the three-in-one mechanism in even greater favour among users and drivers. Most troubles incidental to the use of springs rigidly fitted to the axle casing are traceable to running with loose holding down bolts: Those bolts are severely stressed and should be des;gued and made accordingly, in addition to which, drivers must pay scrupulous attention to keeping them tight and in good order. If the bolts are allowed to remain loose, the centre pin which registers in the spring seating shears, following which some of the failures mentioned by " Spring Drive" may occur. It may be of interest to record the writer's experience with a small fleet of "J" type Thornycroft lorries on war service in France of the most strenuous kind, during two years. Not one rear spring leaf breakage has occurred ; although the severe conditions have caused several front spring breakages.
The flexible ring universal joints have surprised us by their great durability ; which answers another of "Spring Drive's" points against the three-in-one • system_ Until such time as the suspension of solid-tyred vehicles undergoes some drastie change, the combined spring, torque and thrust member must continue to grow in popularity because of its success under war conditions and its many advantages, including: 1.—Low cost of manufacture.
2.—Substantial saving in weight at the right place ; i.e., on the rear axle.
3.—Elimination of several wearing surfaces. demandMg frequent lubrication or renewal, or both.
4.—Elimination of parts liable to break and cause accidents.
5.—Accessibility for cleaning and inspectiOn. 6.—Silence.—Yours faithfully,
E. MITCHELL, Cpl., R.A.S.C.,
Why Not Dual Ignition Always ?
The Editor, THE COMMERCIAL MOTOR.
[1673) Sir,—For four years I have been driving Army lorries in France. On some of those lorries I had no dual ignition ; on others I had the dual system, which generally worked satisfactorily. Where. I had this. system, I found it had many advantages. For one thing, it enabled she to shut off the engine during stops of short duration, and, for another thing, it was useful—often very useful—in starting up on cold mornings. It seems to use that there is only one. argument against a proper dual-ignition system, viz., extra cost. But what is this cost, after all ? Something leas than 1 per cent. Public opinion among lorry users should be educated to the pitch of expecting dual ignition ai a matter of coilrse.—Yours
faithfully, Tom anee: