UNSPRUNG WEIGHT.
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"The Engineer" Follows Up His Recent Arguments on the Absorption the Tyres, and Replies to Comments They Have Evoked. of Shocks by
THE INTERESTING articles on the above subjectwhich have appeared in The Commercial Motor must have a far-reaching effect in throwing pevs light on the solution of the big problem of how to reduce to a minimum unsprung weight in every type of heavy chassis. In my article on the above subject which appeared in The Commercial Motor of December 12th, I drew attention to two important facts, namely, "'Fact 1 " and "Fact 2," and in The Commercial Motor of December 26th there appeared this editorial comment upon them:— " We entirely agree with ' Engineer' in his 'Fact No. I,' under which heading he points out that the matter is largely governed. by cost of running. We think there are no public companies sufficiently broadminded to sacrifice profits to any great extent to save municipal authorities' expenditure on road maintenance, although they may, in every reasonable way, wish to meet them."
I note that the chassis manufacturers are not blamed, as they are assumed to have very little coatrol over the matter. In fact it is editorially stated that the customer who buys the vehicle alone can settle what tyres he shall employ. I admit that, if one refers to solid rubber band tyres, this is quite true, because of to-day's narrow standard wheels. I also admit that the chassis manufacturer is quite justified in having his wheels as narrow as possible when using solid rubber band tyres, because by doing so he reduces the unsprung parts of his vehicle. In other words, a back driving wheel which is 8 ins. wide when fitted with solid rubber band tyres has lessunsprung weight than a wheel which is 9-1 ins. wide and which is shod with solid rubber band tyres of larger section, although it is well known that the wider wheel with the wider section tyres will run longer mileages. I would like, however, to draw special attention to the ail-important fact that, if B28
all unsprung parts in any chassis are to be eliminated in the future, the present narrow types of wheels must be increased in width in order to enable the wheels to be shod with good shock-absorbing tyres which " give " in road contact at least half an inch under minimum load and from three-quarters of an inch up to an inch as and when required under maximum load or shock, and that, by doing so, every unsprung part in all existing types of heavy chassis is automatically turned into a well-sprung part. In other words, by increasing the width and actual weight of existing chassis wheel and shoeing them with good shock-absorbing tyres, as already referred to, the chassis manufacturer is able to eliminate from his chassis all unsprung or badly sprung parts.
The Objections to Widening of Wheels.
I can well understand any chassis manufacturer objecting to widen his wheels in order to take wider solid rubber band tyres, because by doing so he increases the unsprung weight in his chassis, but I cannot believe any chassis owner will object to the widening of his wheels in order to eliminate by one bold stroke every unsprung part in his chassis.
I admit that the chassis manufacturer of to-day has great difficulty in widening his, wheels, because of the abnormal number of standard narrow wheels which are running in this country, and because of his forward contracts for narrow wheels, but surely the advantages of wiping out all unsprung parts by widening his wheels and using good shock-absorbing tyres, as referred to in my article on "Unsprung Weight" in The Commercial Motor of December 12th, is sufficient reward for the trouble entailed in increasing the width of his wheels. Also, surely thi fact that millions of money can be saved yearly in road and chassis upkeep, and that the speed and range of chassis movement per day can be increased, is sufficient inducement for our chassis manufac
turcrs to increase the width of the wheels as soon ss possible!
In addition to the " Facts 1 and 2," I would like to add the following, in order that the readers of The Commercial Motor may understand exactly what can and cannot be done to eradicate the unsprung parts of a chassis.
Fact No. -3.—Every unsprung part in every type of heavy chassis can be turned into,a, well-sprung part by shoeing the chassis with good shockabsorbing tyres which " give" in road contact under minimum load at least half an inch, and under maximum load from three-quarters of an inch up to an inch, as and when required.
Fact No. 4.—Shock-absorbing tyres, as referred to in Fact No. 3, cannot be manufactured to run abnormal mileages unless the base parts of the tyres are manufactured 20 mm. wider than existing solids to carry similar loads, when used on front steering wheels, and 40 mm. wider than existing solids when used on rear driving wheels.
Wider Flanges and Bigger Solid Tyres.
Fact No. 5.—If wheels are manufactured with wider flanges, to enable wide-base shock-absorbing tyres, as referred to in Fact No.4, to be fitted airtightly and efficiently to suitable wide wheels, every part of the chassis becomes automatically a wellsprung part under both minimum and maximum loads, and the speed or range of movement of the chassis per day is abnormally increased.
Fact No. 6.—To enable ideal shock-absorbing tyres, as referred to above, to be manufactured for every type of heavy chassis, the centre line of the tyremust be free to move to enable the rubber (which is practically incompressible), on and about the tyre's centre line, to flex abnormally under light load, and a suitable cushion of confined air must be formed on and about the tyre's centre line to enable the incompressible rubber (which is not free to be displaced in existing types of solid rubber band tyres) to be easily displaced into the confined air chamber prepared for its reception. The above facts, 3, 4, 5, and 6, have been proved during the last 18 months, and it may interest you to know that, when the shock-absorbing tyres referred to above were manufactured the same width as existing solid rubber band tyres, and interchanged. with said tyres to carry similar loads, the mileage they ran was under 10,000 miles, but, when similar tyres were manufactured on exactly the same principle, but having a wider base foundation, these tyres ran over 30,000 miles. Also, these shockabsorbing tyres, when running under minimum load, had always a " give " in road contact of at least half an inch under minimum load and from threequarters of an inch up to an inch under maximum load.
Springing the "Unsprung Parts."
In other words, every unsprung part of a chassis when shod with such tyres automatically becomes a well-sprung part, even -under minimum load.
It takes a long time to prove the commercial value of any chassis part, particularly if the part referred to is a tyre, because thousands of miles must be run off on different types of chassis at many speeds, on various roads and in all weathers, before it is proved in practice on the road that a new theory (particularly in tyres) is not only correct, but is also of great commercial value.
In the valuable article on this subject, the opinion is editorially expressed that " Engineer" is a little too sanguine and has written as if this big problem of eliminating all the unsprung weight of a heavy chassis, by means of a good shock-absorbing tyre, had been solved up to the hilt, and in reply I beg to say that in the article which appeared in The Commercial Motor of November 28th, in the last paragraph the following is stated:— " We shall be glad to hear any practical sugges tions from Engineer,' or anyone else, provided that some real remedy is suggested, because road wear and vibration from passing vehiclesare constant sources of complaint-, and their reduction is ever being sought," and in my article which appeared in The Commercial Motor of December 12th, I consplied with your request, but I did not state that the problem had been solved 11D to the hilt, because such a problem cannot be solved tip to the hilt until a big demand has been created and the good shockabsorbing tyres referred to herein are fitted to every type of heavy commercial vehicle. In the article in The Commercial Motor of December 26th, it is said that the customer controls tyre sizes, but I think it will be admitted that a customer cannot control tyre -widths if the chassis manufacturer controls, standardizes, and limits the width of his wheels.
With regard to inflated tyres, it is now admitted by our British tyre manufacturers that, the canvas foundation tyre of yesterday is a very poor substitide for the shock-absorbing cord foundation tyres of to-day (which also save petrol), but, unfortunately, our British-tyre manufacturers did not at first agree that there was any practical advantage in running inflated tyres with low air pressures and thereby springing efficiently the unsprung or badly sprung parts of the pleasure chassis when running under minimum loads, with the result that the foreign tyre manufacturer stepped in and supplied this country with the inflated type of good shockabsorbing cord foundation tyres so badly wanted by every private chassis owner, and I am afraid that, if our British chassis manufacturers do not supply as wide wheels as are being used abroad, the foreigner, with his wider standardized wheels, will again step in and secure the greater part of the commercial tyre trade of this country.
Freeing the Centre Line of a Tyre.
I admit that the tyre manufacturers did-not (or could, not), in the past, produce the ideal shockabsorbing heavy commercial tyre so badly wanted for heavy chassisI also admit that the tyre manufacturers have, in the past, made many attempts to manufacture the right type of shock-absorbing noninflated tyre so badly wanted everywhere by every heavy chassis owner, and have utterly failed to do so, because of the fact that they did not realize the abnormal importance of freeing efficiently the tyre's centre line to enable the tyre, when in road contact, to flex efficiently under minimum load, in combination with the use of confined air at low pressures, in order to obtain abnormal shock-absorbing qualities and increased speed, unobtainable in existing types of road-destroying solid rubber band tyres. Referring to a letter signed " -which appeared in the correspondence columns of The Commercial Motor of December 26th, on " Unsprung Weight," I beg to point out to the writer that -Fig. 2 does not show an inflated tyre running flat, or nearly so as suggested in his letter, but shows an
inflated so, (having cord foundations and a tread which automatically narrows or widens in effect, according to the load carried or shock received) passing over a pot-hole or backing against a kerbstone, or absorbing an abnormal road obstruction, when, for a moment of time, it is capable of flexing up to 1 inches without injuring the tyre.
" C.M.L." states that, in his opinion, it has yet to be proved that any form of inflated tyre can run satisfactorily unless fairly fully inflated. How can he make such a statement, considering that there are running in this country many thousands of foreignmanufactured inflated tyres with 45 lb. to 50 lb. pressure, whilst a British tyre manufacturer guarantees his tyres for a minimum of 5,000 miles and advises his tyre users to keep the air pressure down to 45 lb.' in order to obtain abnormal luxury and comfort by means of his (guaranteed mileage; tyres?