Tyre Conservation and Timely Repair
Page 35
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• A Designer and Inventor With a Long Experience of Road Transport Reviews the Factors Which Lead to "SpottyWear of Tyres and Puts Forward Some Interesting Theories
By
F. W. Baker AIS a trader', interested in tyre and rubber conserVation, am disappointed and surprised that The important Goodyear article in your issue dated July 9 has attracted only a single cohurient.Surely some of the " big. noises " in the motor world ought to sit up and take notice, and let traders hear from them 'as to the import
ance of delving into the why and wherefore of this, to use Mr. Cressalla's apt description, " grave waste of tyre mileage."
These " incidents " do not happen without cause, and . the One and only reasen for the Seridus: damage illustrated Is that something is " out of line," that is to say, in some form 'or other, the laws of nature are being interfered with.
In our student days, when we were taught the theories of forces, we were told—and, as with other laws of nature, this" telling "holds good to-day—that all bodies, moving around, a centre or fixed point have a tendency to fly off in a straight line, This is ternied centrifugal force. It is opposed to centripetal force, Or that power which maintains a body in its curvilineal path, and the damage to the Goodyear fleet, 50 ably illustrated, exposes interference,
mechanical or otherwise, -with these natural laws. • , Effect of Disturbing Laws of Motion
Reverting to the Goodyear report, the mechanical irregularities in hub and axle assemblies would be transferrect to regularitie,r if, for example; a wheel was seriously outof balance, because it would not result in a series of spots, but would show-extra wear at a given, point. These trailer wheels are not therefore necessarily out of balance, but the spots, as Goodyears describe therri, are .obviously caused by disturbing the laws of motion.
Here is an example. The principle of the RudgeWhitworth detachable wheel is that the huh revolves faster than the locknut, and that the two parts are, in. inverse proportion to the relative length of their circumferentes. In other words, when first assembled, they do not move equally or synchronize, as a whole, until, under the laws of motion, the locknut tightens itself by virtue of the frictional contact of the co-acting surfates, and in the event of displacement, brought about by reversing or other cause, the same action restores the assembly to normal on going forward. In other words, the laws of motion support, TecO,VEry, but, under the same laws,. the: faulty bearing, caused by disobedience to the law by stress, strain or defect, has no such means for recovery, and immediately becomes out of rhythm or regularity With the_point of _road contact, and this explains the spotted wear.
The same argument supports, indirectly, the problem of twin :tyres; also that errors in motion or velocity take the path of least resistance. Now the path or line of Connection, leading from the point of road contact to the' point in the bearing, directs or confines itself to one cOunnunicating angle, and at the bearing end of this angle ahe,ininer fault is emphasized until it becomes a major' fault which fractures the bearing. The angle of connection is coupled only with' one tyre, because there is only one track of least • resistance, • and that track cannot synchronize with the point of road contact, because the 'bearing sailers are travelling faster than th.e tyre. This would seem to be an explanation for what Goodyear quotes as the hithertodifficult problem tor which a solution has long been sought.
When, therefore, we seek the cause for the faulty bearing. we can see. daylight. We know that to-day's rollerbearing is as near to perfection as damn-it is to swearit'er, bbt it is not near enough to " argue the point ". with the laiVs of motion, If one or twobearings in a fleet of 500 went groggy " we should probably not be:alarreed,:, but -two bar-reit:Ms of bad-bearings,as• recorded by ":Tfatispbrt Topics,." in.-this fleet of .500, 14.0 wrecked tyres in
consequence, is too much to. ask ns swolloW.
Goodyears tell us that the condition is generally confined to trailers or semi-trailers, but doet not inforin us whether the spots bemore pronounced under load, Now
I know something of these Goodyear tests.. One of their •
:stall, with. whom I rode from Akron to Cleveland, some year ago, in discussing them reminded. me -that it was not a question ot'Akmn to Cleveland, but, sometimes (and this meant many times) loaded Lorries were sent out on fourfigure Mile jburneys over the :Rockies and along menin
• tainous roads, which have no relation to our English roads.
HasWell tells us that " a wheel and axle is -a revolving lever:" Goodyear's tell us that in a fleet of 500 trailers the wheel` doctor found two barrelfuls of bad bearings. Reaction on an unloaded trailer,being driven around hilly and rutty corners' at speed, obviously faster without load than under' load, would invite multiple causes, for spotty wear, because speed is a disturbing factor. The 'centrifugal forces are .proportioual to the square of the velocity, so that at 10 r.p.tn. the force's are four times
greater than at 5 r.p.m: . .
Unloaded. trailer wheels, when the driver wants to set back home, may perform all sorts of monkey tricks without a controlling liad„and, possibly, some of these . damaged bearings are due to centripetal reaction, which,unfortunately, has not,. so far, figured very largely in the minds of wheel engineers and designers, because,. when., years ago, at that stage whenthe trade was changing froin detachable rims to detachable wheels, and road-transport men were having trouble with wheel breakages, the. reaction of manufacturers and wheel designers was to build wheels heavier. In building them heavier, hubs and other structural parts were ordered correspondingly heavier, until to-day's commercial vehicle is a very Weighty job,-.calling
for stronger and heavier tyres. .
By the way. I wonder if our Goodyear friends have given a thought to Wooden wheels for their trailers. I could tell them a stork—and a true one—about proof in the infinitesimal "give " of a wooden wheel under test which they would query, but the reminder may give them something
to think about,
What is Demanded from a Tyre -Mist pi us, in bur ,search for wheel and tyre knowledge, . have Visited one or other of -the Tyre Economy Exhibitions prorhoted by Tyre Control, and many of us practical fellows . have wOndered if they be justified. In this direction I wonder how many of us tyre and wheel " birds l' . realize what we demand from tyres. Until 19 years ago, when I heard a paper read at Cleveland, Ohio, on the advent of the balloon tyre, I did. not. It was given by a Mi.. J. Hale—Jim .Hale to his pals--a,t The Hotel Winton, and he was connected with the Goodyear or` Firestone organization. His subject 'was flexing, when he retninded ii that a Motor tyre, in rendering 15000 miles' service, revolved 10,000,1100 times, during which, each and. every part of the canvas Must flex the .same number of times, Within a yard Di my desk I have a tyre which, on one of my test cars, has covered 75,000 -.miles, and without consulting ,u ready-reckoner or a. text-book, I am taking Jim Hale 's word for it that it has resolved in service 50,000,000 times. JUst think of it, but don't ask me how many times the point of road contact, revolving sloWer than the bearing.roller, would, in the event of a faulty roller or cage;
have "clicked.'' ' • Going back to Haswell, it is only common sense to surmise that; if a wheel and axle be•a revolving lever, and if' the leverage .beedmes -disproportionately actioriable, whether loaded or unloaded, around sharp. bends and rough roadsa the rollers or other parts, however well made, become sub
ject to :more uneven snatches. and s:tresaes. . . There is a remedy, and t am prepared to prove by. road: :tests running into a miieage_of six figere'S, that the probe lem can be dealt with.. Briefly, :it can he" doctored " by lesseningthe peripheral wheel 'weight, and it can be cured by a practical' coromon-sense method of axle cushioning.